TY - JOUR
AU - Archer, Lynden A.
AU - Bruce, Peter G.
AU - Calvo, Ernesto J.
AU - Dewar, Daniel
AU - Ellison, James H. J.
AU - Freunberger, Stefan Alexander
AU - Gao, Xiangwen
AU - Hardwick, Laurence J.
AU - Horwitz, Gabriela
AU - Janek, Jürgen
AU - Johnson, Lee R.
AU - Jordan, Jack W.
AU - Matsuda, Shoichi
AU - Menkin, Svetlana
AU - Mondal, Soumyadip
AU - Qiu, Qianyuan
AU - Samarakoon, Thukshan
AU - Temprano, Israel
AU - Uosaki, Kohei
AU - Vailaya, Ganesh
AU - Wachsman, Eric D.
AU - Wu, Yiying
AU - Ye, Shen
ID - 14701
JF - Faraday Discussions
KW - Physical and Theoretical Chemistry
SN - 1359-6640
TI - Towards practical metal–oxygen batteries: General discussion
ER -
TY - JOUR
AB - The short history of research on Li-O2 batteries has seen a remarkable number of mechanistic U-turns over the years. From the initial use of carbonate electrolytes, that were then found to be entirely unsuitable, to the belief that (su)peroxide was solely responsible for degradation, before the more reactive singlet oxygen was found to form, to the hypothesis that capacity depends on a competing surface/solution mechanism before a practically exclusive solution mechanism was identified. Herein, we argue for an ever-fresh look at the reported data without bias towards supposedly established explanations. We explain how the latest findings on rate and capacity limits, as well as the origin of side reactions, are connected via the disproportionation (DISP) step in the (dis)charge mechanism. Therefrom, directions emerge for the design of electrolytes and mediators on how to suppress side reactions and to enable high rate and high reversible capacity.
AU - Jethwa, Rajesh B
AU - Mondal, Soumyadip
AU - Pant, Bhargavi
AU - Freunberger, Stefan Alexander
ID - 14687
JF - Angewandte Chemie International Edition
KW - General Chemistry
KW - Catalysis
SN - 1433-7851
TI - To DISP or not? The far‐reaching reaction mechanisms underpinning Lithium‐air batteries
ER -
TY - JOUR
AB - Singlet oxygen (1O2) formation is now recognised as a key aspect of non-aqueous oxygen redox chemistry. For identifying 1O2, chemical trapping via 9,10-dimethylanthracene (DMA) to form the endoperoxide (DMA-O2) has become the mainstay method due to its sensitivity, selectivity, and ease of use. While DMA has been shown to be selective for 1O2, rather than forming DMA-O2 with a wide variety of potentially reactive O-containing species, false positives might hypothetically be obtained in the presence of previously overlooked species. Here, we first give unequivocal direct spectroscopic proof by the 1O2-specific near infrared (NIR) emission at 1270 nm for the previously proposed 1O2 formation pathways, which centre around superoxide disproportionation. We then show that peroxocarbonates, common intermediates in metal-O2 and metal carbonate electrochemistry, do not produce false-positive DMA-O2. Moreover, we identify a previously unreported 1O2-forming pathway through the reaction of CO2 with superoxide. Overall, we give unequivocal proof for 1O2 formation in non-aqueous oxygen redox and show that chemical trapping with DMA is a reliable method to assess 1O2 formation.
AU - Mondal, Soumyadip
AU - Jethwa, Rajesh B
AU - Pant, Bhargavi
AU - Hauschild, Robert
AU - Freunberger, Stefan Alexander
ID - 13044
JF - Faraday Discussions
KW - Physical and Theoretical Chemistry
SN - 1359-6640
TI - Singlet oxygen in non-aqueous oxygen redox: Direct spectroscopic evidence for formation pathways and reliability of chemical probes
ER -
TY - JOUR
AB - Capacity, rate performance, and cycle life of aprotic Li–O2 batteries critically depend on reversible electrodeposition of Li2O2. Current understanding states surface-adsorbed versus solvated LiO2 controls Li2O2 growth as surface film or as large particles. Herein, we show that Li2O2 forms across a wide range of electrolytes, carbons, and current densities as particles via solution-mediated LiO2 disproportionation, bringing into question the prevalence of any surface growth under practical conditions. We describe a unified O2 reduction mechanism, which can explain all found capacity relations and Li2O2 morphologies with exclusive solution discharge. Determining particle morphology and achievable capacities are species mobilities, true areal rate, and the degree of LiO2 association in solution. Capacity is conclusively limited by mass transport through the tortuous Li2O2 rather than electron transport through a passivating Li2O2 film. Provided that species mobilities and surface growth are high, high capacities are also achieved with weakly solvating electrolytes, which were previously considered prototypical for low capacity via surface growth.
AU - Prehal, Christian
AU - Mondal, Soumyadip
AU - Lovicar, Ludek
AU - Freunberger, Stefan Alexander
ID - 12065
IS - 9
JF - ACS Energy Letters
TI - Exclusive solution discharge in Li-O₂ batteries?
VL - 7
ER -
TY - JOUR
AB - The inadequate understanding of the mechanisms that reversibly convert molecular sulfur (S) into lithium sulfide (Li2S) via soluble polysulfides (PSs) formation impedes the development of high-performance lithium-sulfur (Li-S) batteries with non-aqueous electrolyte solutions. Here, we use operando small and wide angle X-ray scattering and operando small angle neutron scattering (SANS) measurements to track the nucleation, growth and dissolution of solid deposits from atomic to sub-micron scales during real-time Li-S cell operation. In particular, stochastic modelling based on the SANS data allows quantifying the nanoscale phase evolution during battery cycling. We show that next to nano-crystalline Li2S the deposit comprises solid short-chain PSs particles. The analysis of the experimental data suggests that initially, Li2S2 precipitates from the solution and then is partially converted via solid-state electroreduction to Li2S. We further demonstrate that mass transport, rather than electron transport through a thin passivating film, limits the discharge capacity and rate performance in Li-S cells.
AU - Prehal, Christian
AU - von Mentlen, Jean-Marc
AU - Drvarič Talian, Sara
AU - Vizintin, Alen
AU - Dominko, Robert
AU - Amenitsch, Heinz
AU - Porcar, Lionel
AU - Freunberger, Stefan Alexander
AU - Wood, Vanessa
ID - 12208
JF - Nature Communications
KW - General Physics and Astronomy
KW - General Biochemistry
KW - Genetics and Molecular Biology
KW - General Chemistry
KW - Multidisciplinary
SN - 2041-1723
TI - On the nanoscale structural evolution of solid discharge products in lithium-sulfur batteries using operando scattering
VL - 13
ER -
TY - JOUR
AB - Polydicyclopentadiene (pDCPD), a thermoset with excellent mechanical properties, has enormous potential as a lightweight, tough, and stable matrix material owing to its highly cross-linked macromolecular network. This work describes generating pDCPD-based foams and hierarchically porous carbons derived therefrom by combining ring-opening metathesis polymerization (ROMP) of DCPD, high internal phase emulsions (HIPEs) as structural templates, and subsequent carbonization. The structure and function of the carbon foams were characterized and discussed in detail using scanning electron, transmission electron, or atomic force microscopy (SEM, TEM, AFM), electron energy-loss spectroscopy (TEM-EELS), N2 sorption, and analyses of electrical conductivity as well as mechanical properties. The resulting materials exhibited uniform, shape-retaining shrinkage of only ∼1/3 after carbonization. No structural failure was observed even when the pDCPD precursor foams were heated to 1400 °C. Instead, the high porosity, void size, and 3D interconnectivity were fully preserved, and the void diameters could be adjusted between 87 and 2.5 μm. Moreover, foams have a carbon content >97%, an electronic conductivity of up to 2800 S·m–1, a Young’s modulus of up to 2.1 GPa, and a specific surface area of up to 1200 m2·g–1. Surprisingly, the pDCPD foams were carbonized into shapes other than monoliths, such as 10’s of micron thick membranes or foamy coatings adhered to a metal foil or grid substrate. The latter coatings even adhere upon bending. Finally, as a use case, carbonized foams were applied as porous cathodes for Li–O2 batteries where the foams show a favorable combination of porosity, active surface area, and pore size for outstanding capacity.
AU - Kovačič, Sebastijan
AU - Schafzahl, Bettina
AU - Matsko, Nadejda B.
AU - Gruber, Katharina
AU - Schmuck, Martin
AU - Koller, Stefan
AU - Freunberger, Stefan Alexander
AU - Slugovc, Christian
ID - 12227
IS - 11
JF - ACS Applied Energy Materials
KW - Electrical and Electronic Engineering
KW - Materials Chemistry
KW - Electrochemistry
KW - Energy Engineering and Power Technology
KW - Chemical Engineering (miscellaneous)
SN - 2574-0962
TI - Carbon foams via ring-opening metathesis polymerization of emulsion templates: A facile method to make carbon current collectors for battery applications
VL - 5
ER -
TY - JOUR
AB - Redox mediators could catalyse otherwise slow and energy-inefficient cycling of Li–S and Li–O2 batteries by shuttling electrons or holes between the electrode and the solid insulating storage materials. For mediators to work efficiently they need to oxidize the solid with fast kinetics but with the lowest possible overpotential. However, the dependence of kinetics and overpotential is unclear, which hinders informed improvement. Here, we find that when the redox potentials of mediators are tuned via, for example, Li+ concentration in the electrolyte, they exhibit distinct threshold potentials, where the kinetics accelerate several-fold within a range as small as 10 mV. This phenomenon is independent of types of mediator and electrolyte. The acceleration originates from the overpotentials required to activate fast Li+/e− extraction and the following chemical step at specific abundant surface facets. Efficient redox catalysis at insulating solids therefore requires careful consideration of the surface conditions of the storage materials and electrolyte-dependent redox potentials, which may be tuned by salt concentrations or solvents.
AU - Cao, Deqing
AU - Shen, Xiaoxiao
AU - Wang, Aiping
AU - Yu, Fengjiao
AU - Wu, Yuping
AU - Shi, Siqi
AU - Freunberger, Stefan Alexander
AU - Chen, Yuhui
ID - 10813
JF - Nature Catalysis
KW - Process Chemistry and Technology
KW - Biochemistry
KW - Bioengineering
KW - Catalysis
SN - 2520-1158
TI - Threshold potentials for fast kinetics during mediated redox catalysis of insulators in Li–O2 and Li–S batteries
VL - 5
ER -
TY - GEN
AB - Insufficient understanding of the mechanism that reversibly converts sulphur into lithium sulphide (Li2S) via soluble polysulphides (PS) hampers the realization of high performance lithium-sulphur cells. Typically Li2S formation is explained by direct electroreduction of a PS to Li2S; however, this is not consistent with the size of the insulating Li2S deposits. Here, we use in situ small and wide angle X-ray scattering (SAXS/WAXS) to track the growth and dissolution of crystalline and amorphous deposits from atomic to sub-micron scales during charge and discharge. Stochastic modelling based on the SAXS data allows quantification of the chemical phase evolution during discharge and charge. We show that Li2S deposits predominantly via disproportionation of transient, solid Li2S2 to form primary Li2S crystallites and solid Li2S4 particles. We further demonstrate that this process happens in reverse during charge. These findings show that the discharge capacity and rate capability in Li-S battery cathodes are therefore limited by mass transport through the increasingly tortuous network of Li2S / Li2S4 / carbon pores rather than electron transport through a passivating surface film.
AU - Prehal, Christian
AU - Talian, Sara Drvarič
AU - Vizintin, Alen
AU - Amenitsch, Heinz
AU - Dominko, Robert
AU - Freunberger, Stefan Alexander
AU - Wood, Vanessa
ID - 9980
KW - Li2S
KW - Lithium Sulphur Batteries
KW - SAXS
KW - WAXS
T2 - Research Square
TI - Mechanism of Li2S formation and dissolution in Lithium-Sulphur batteries
ER -
TY - JOUR
AB - “Hydrogen economy” could enable a carbon-neutral sustainable energy chain. However, issues with safety, storage, and transport of molecular hydrogen impede its realization. Alcohols as liquid H2 carriers could be enablers, but state-of-the-art reforming is difficult, requiring high temperatures >200 °C and pressures >25 bar, and the resulting H2 is carbonized beyond tolerance levels for direct use in fuel cells. Here, we demonstrate ambient temperature and pressure alcohol reforming in a fuel cell (ARFC) with a simultaneous electrical power output. The alcohol is oxidized at the alkaline anode, where the resulting CO2 is sequestrated as carbonate. Carbon-free H2 is liberated at the acidic cathode. The neutralization energy between the alkaline anode and the acidic cathode drives the process, particularly the unusually high entropy gain (1.27-fold ΔH). The significantly positive temperature coefficient of the resulting electromotive force allows us to harvest a large fraction of the output energy from the surrounding, achieving a thermodynamic efficiency as high as 2.27. MoS2 as the cathode catalyst allows alcohol reforming even under open-air conditions, a challenge that state-of-the-art alcohol reforming failed to overcome. We further show reforming of a wide range of alcohols. The ARFC offers an unprecedented route toward hydrogen economy as CO2 is simultaneously captured and pure H2 produced at mild conditions.
AU - Manzoor Bhat, Zahid Manzoor
AU - Thimmappa, Ravikumar
AU - Dargily, Neethu Christudas
AU - Raafik, Abdul
AU - Kottaichamy, Alagar Raja
AU - Devendrachari, Mruthyunjayachari Chattanahalli
AU - Itagi, Mahesh
AU - Makri Nimbegondi Kotresh, Harish
AU - Freunberger, Stefan Alexander
AU - Ottakam Thotiyl, Musthafa
ID - 9113
IS - 8
JF - ACS Sustainable Chemistry and Engineering
TI - Ambient condition alcohol reforming to hydrogen with electricity output
VL - 9
ER -
TY - JOUR
AB - Electrodepositing insulating lithium peroxide (Li2O2) is the key process during discharge of aprotic Li–O2 batteries and determines rate, capacity, and reversibility. Current understanding states that the partition between surface adsorbed and dissolved lithium superoxide governs whether Li2O2 grows as a conformal surface film or larger particles, leading to low or high capacities, respectively. However, better understanding governing factors for Li2O2 packing density and capacity requires structural sensitive in situ metrologies. Here, we establish in situ small- and wide-angle X-ray scattering (SAXS/WAXS) as a suitable method to record the Li2O2 phase evolution with atomic to submicrometer resolution during cycling a custom-built in situ Li–O2 cell. Combined with sophisticated data analysis, SAXS allows retrieving rich quantitative structural information from complex multiphase systems. Surprisingly, we find that features are absent that would point at a Li2O2 surface film formed via two consecutive electron transfers, even in poorly solvating electrolytes thought to be prototypical for surface growth. All scattering data can be modeled by stacks of thin Li2O2 platelets potentially forming large toroidal particles. Li2O2 solution growth is further justified by rotating ring-disk electrode measurements and electron microscopy. Higher discharge overpotentials lead to smaller Li2O2 particles, but there is no transition to an electronically passivating, conformal Li2O2 coating. Hence, mass transport of reactive species rather than electronic transport through a Li2O2 film limits the discharge capacity. Provided that species mobilities and carbon surface areas are high, this allows for high discharge capacities even in weakly solvating electrolytes. The currently accepted Li–O2 reaction mechanism ought to be reconsidered.
AU - Prehal, Christian
AU - Samojlov, Aleksej
AU - Nachtnebel, Manfred
AU - Lovicar, Ludek
AU - Kriechbaum, Manfred
AU - Amenitsch, Heinz
AU - Freunberger, Stefan Alexander
ID - 9301
IS - 14
JF - Proceedings of the National Academy of Sciences
KW - small-angle X-ray scattering
KW - oxygen reduction
KW - disproportionation
KW - Li-air battery
SN - 0027-8424
TI - In situ small-angle X-ray scattering reveals solution phase discharge of Li–O2 batteries with weakly solvating electrolytes
VL - 118
ER -
TY - JOUR
AB - Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) based water-in-salt electrolytes (WiSEs) has recently emerged as a new promising class of electrolytes, primarily owing to their wide electrochemical stability windows (~3–4 V), that by far exceed the thermodynamic stability window of water (1.23 V). Upon increasing the salt concentration towards superconcentration the onset of the oxygen evolution reaction (OER) shifts more significantly than the hydrogen evolution reaction (HER) does. The OER shift has been explained by the accumulation of hydrophobic anions blocking water access to the electrode surface, hence by double layer theory. Here we demonstrate that the processes during oxidation are much more complex, involving OER, carbon and salt decomposition by OER intermediates, and salt precipitation upon local oversaturation. The positive shift in the onset potential of oxidation currents was elucidated by combining several advanced analysis techniques: rotating ring-disk electrode voltammetry, online electrochemical mass spectrometry, and X-ray photoelectron spectroscopy, using both dilute and superconcentrated electrolytes. The results demonstrate the importance of reactive OER intermediates and surface films for electrolyte and electrode stability and motivate further studies of the nature of the electrode.
AU - Maffre, Marion
AU - Bouchal, Roza
AU - Freunberger, Stefan Alexander
AU - Lindahl, Niklas
AU - Johansson, Patrik
AU - Favier, Frédéric
AU - Fontaine, Olivier
AU - Bélanger, Daniel
ID - 9447
IS - 5
JF - Journal of The Electrochemical Society
KW - Renewable Energy
KW - Sustainability and the Environment
KW - Electrochemistry
KW - Materials Chemistry
KW - Electronic
KW - Optical and Magnetic Materials
KW - Surfaces
KW - Coatings and Films
KW - Condensed Matter Physics
SN - 0013-4651
TI - Investigation of electrochemical and chemical processes occurring at positive potentials in “Water-in-Salt” electrolytes
VL - 168
ER -
TY - GEN
AB - Redox mediators could catalyse otherwise slow and energy-inefficient cycling of Li-S and Li-O 2 batteries by shuttling electrons/holes between the electrode and the solid insulating storage materials. For mediators to work efficiently they need to oxidize the solid with fast kinetics yet the lowest possible overpotential. Here, we found that when the redox potentials of mediators are tuned via, e.g., Li + concentration in the electrolyte, they exhibit distinct threshold potentials, where the kinetics accelerate several-fold within a range as small as 10 mV. This phenomenon is independent of types of mediators and electrolyte. The acceleration originates from the overpotentials required to activate fast Li + /e – extraction and the following chemical step at specific abundant surface facets. Efficient redox catalysis at insulating solids requires therefore carefully considering the surface conditions of the storage materials and electrolyte-dependent redox potentials, which may be tuned by salt concentrations or solvents.
AU - Cao, Deqing
AU - Shen, Xiaoxiao
AU - Wang, Aiping
AU - Yu, Fengjiao
AU - Wu, Yuping
AU - Shi, Siqi
AU - Freunberger, Stefan Alexander
AU - Chen, Yuhui
ID - 9978
KW - Catalysis
KW - Energy engineering
KW - Materials theory and modeling
T2 - Research Square
TI - Sharp kinetic acceleration potentials during mediated redox catalysis of insulators
ER -
TY - JOUR
AB - Aprotic alkali metal–O2 batteries face two major obstacles to their chemistry occurring efficiently, the insulating nature of the formed alkali superoxides/peroxides and parasitic reactions that are caused by the highly reactive singlet oxygen (1O2). Redox mediators are recognized to be key for improving rechargeability. However, it is unclear how they affect 1O2 formation, which hinders strategies for their improvement. Here we clarify the mechanism of mediated peroxide and superoxide oxidation and thus explain how redox mediators either enhance or suppress 1O2 formation. We show that charging commences with peroxide oxidation to a superoxide intermediate and that redox potentials above ~3.5 V versus Li/Li+ drive 1O2 evolution from superoxide oxidation, while disproportionation always generates some 1O2. We find that 1O2 suppression requires oxidation to be faster than the generation of 1O2 from disproportionation. Oxidation rates decrease with growing driving force following Marcus inverted-region behaviour, establishing a region of maximum rate.
AU - Petit, Yann K.
AU - Mourad, Eléonore
AU - Prehal, Christian
AU - Leypold, Christian
AU - Windischbacher, Andreas
AU - Mijailovic, Daniel
AU - Slugovc, Christian
AU - Borisov, Sergey M.
AU - Zojer, Egbert
AU - Brutti, Sergio
AU - Fontaine, Olivier
AU - Freunberger, Stefan Alexander
ID - 9250
IS - 5
JF - Nature Chemistry
KW - General Chemistry
KW - General Chemical Engineering
SN - 1755-4330
TI - Mechanism of mediated alkali peroxide oxidation and triplet versus singlet oxygen formation
VL - 13
ER -
TY - CHAP
AB - Rechargeable Li–O2 batteries have gathered enormous attention in the research community for having amongst the highest theoretical energy storage. Realizing the promise, even in part, in practice could produce a device that stores significantly more energy than other rechargeable batteries. Fundamental understanding of the reaction mechanisms is now realized to be key to overcome many challenges. We give a critical overview of the current understanding of the chemistry underpinning the Li–O2 cell with focus on the cathode and give a perspective on the most important research needs. Since performance and reversibility are often grossly misunderstood, we put emphasis on realistic performances to be achieved by Li–O2 cells and on means to identify reversibility. Parasitic chemistry is the foremost barrier for reversible cycling and now realized to be predominantly caused by singlet oxygen rather than by the previously thought superoxide or peroxide. This finding profoundly affects any other area of research from reaction mechanisms, to electrolytes and catalysts and dominates future research needs.
AU - Petit, Yann K.
AU - Mourad, Eléonore
AU - Freunberger, Stefan Alexander
ID - 7591
SN - 9783527302505
T2 - Encyclopedia of Electrochemistry
TI - Lithium–Oxygen batteries
ER -
TY - GEN
AB - Here, we employ micro- and nanosized cellulose particles, namely paper fines and cellulose
nanocrystals, to induce hierarchical organization over a wide length scale. After processing
them into carbonaceous materials, we demonstrate that these hierarchically organized materials
outperform the best materials for supercapacitors operating with organic electrolytes reported
in literature in terms of specific energy/power (Ragone plot) while showing hardly any capacity
fade over 4,000 cycles. The highly porous materials feature a specific surface area as high as
2500 m2ˑg-1 and exhibit pore sizes in the range of 0.5 to 200 nm as proven by scanning electron
microscopy and N2 physisorption. The carbonaceous materials have been further investigated
by X-ray photoelectron spectroscopy and RAMAN spectroscopy. Since paper fines are an
underutilized side stream in any paper production process, they are a cheap and highly available
feedstock to prepare carbonaceous materials with outstanding performance in electrochemical
applications.
AU - Hobisch, Mathias A.
AU - Mourad, Eléonore
AU - Fischer, Wolfgang J.
AU - Prehal, Christian
AU - Eyley, Samuel
AU - Childress, Anthony
AU - Zankel, Armin
AU - Mautner, Andreas
AU - Breitenbach, Stefan
AU - Rao, Apparao M.
AU - Thielemans, Wim
AU - Freunberger, Stefan Alexander
AU - Eckhart, Rene
AU - Bauer, Wolfgang
AU - Spirk, Stefan
ID - 8081
TI - High specific capacitance supercapacitors from hierarchically organized all-cellulose composites
ER -
TY - JOUR
AB - Large overpotentials upon discharge and charge of Li-O2 cells have motivated extensive research into heterogeneous solid electrocatalysts or non-carbon electrodes with the aim to improve rate capability, round-trip efficiency and cycle life. These features are equally governed by parasitic reactions, which are now recognized to be caused by the highly reactive singlet oxygen (1O2). However, the link between the presence of electrocatalysts and 1O2 formation in metal-O2 cells is unknown. Here, we show that, compared to pristine carbon black electrodes, a representative selection of electrocatalysts or non-carbon electrodes (noble metal, transition metal compounds) may both slightly reduce or severely increase the 1O2 formation. The individual reaction steps, where the surfaces impact the 1O2 yield are deciphered, showing that 1O2 yield from superoxide disproportionation as well as the decomposition of trace H2O2 are sensitive to catalysts. Transition metal compounds in general are prone to increase 1O2.
AU - Samojlov, Aleksej
AU - Schuster, David
AU - Kahr, Jürgen
AU - Freunberger, Stefan Alexander
ID - 7672
IS - 12
JF - Electrochimica Acta
TI - Surface and catalyst driven singlet oxygen formation in Li-O2 cells
VL - 362
ER -
TY - GEN
AB - With the lithium-ion technology approaching its intrinsic limit with graphite-based anodes, lithium metal is recently receiving renewed interest from the battery community as potential high capacity anode for next-generation rechargeable batteries. In this focus paper, we review the main advances in this field since the first attempts in the
mid-1970s. Strategies for enabling reversible cycling and avoiding dendrite growth are thoroughly discussed, including specific applications in all-solid-state (polymeric and inorganic), Lithium-sulphur and Li-O2 (air) batteries. A particular attention is paid to review recent developments in regard of prototype manufacturing and current state-ofthe-art of these battery technologies with respect to the 2030 targets of the EU Integrated Strategic Energy Technology Plan (SET-Plan) Action 7.
AU - Varzi, Alberto
AU - Thanner, Katharina
AU - Scipioni, Roberto
AU - Di Lecce, Daniele
AU - Hassoun, Jusef
AU - Dörfler, Susanne
AU - Altheus, Holger
AU - Kaskel, Stefan
AU - Prehal, Christian
AU - Freunberger, Stefan Alexander
ID - 8067
KW - Battery
KW - Lithium metal
KW - Lithium-sulphur
KW - Lithium-air
KW - All-solid-state
SN - 2664-1690
TI - Current status and future perspectives of Lithium metal batteries
ER -
TY - JOUR
AB - With the lithium-ion technology approaching its intrinsic limit with graphite-based anodes, Li metal is recently receiving renewed interest from the battery community as potential high capacity anode for next-generation rechargeable batteries. In this focus paper, we review the main advances in this field since the first attempts in the mid-1970s. Strategies for enabling reversible cycling and avoiding dendrite growth are thoroughly discussed, including specific applications in all-solid-state (inorganic and polymeric), Lithium–Sulfur (Li–S) and Lithium-O2 (air) batteries. A particular attention is paid to recent developments of these battery technologies and their current state with respect to the 2030 targets of the EU Integrated Strategic Energy Technology Plan (SET-Plan) Action 7.
AU - Varzi, Alberto
AU - Thanner, Katharina
AU - Scipioni, Roberto
AU - Di Lecce, Daniele
AU - Hassoun, Jusef
AU - Dörfler, Susanne
AU - Altheus, Holger
AU - Kaskel, Stefan
AU - Prehal, Christian
AU - Freunberger, Stefan Alexander
ID - 8361
IS - 12
JF - Journal of Power Sources
SN - 0378-7753
TI - Current status and future perspectives of lithium metal batteries
VL - 480
ER -
TY - JOUR
AB - Aqueous iodine based electrochemical energy storage is considered a potential candidate to improve sustainability and performance of current battery and supercapacitor technology. It harnesses the redox activity of iodide, iodine, and polyiodide species in the confined geometry of nanoporous carbon electrodes. However, current descriptions of the electrochemical reaction mechanism to interconvert these species are elusive. Here we show that electrochemical oxidation of iodide in nanoporous carbons forms persistent solid iodine deposits. Confinement slows down dissolution into triiodide and pentaiodide, responsible for otherwise significant self-discharge via shuttling. The main tools for these insights are in situ Raman spectroscopy and in situ small and wide-angle X-ray scattering (in situ SAXS/WAXS). In situ Raman confirms the reversible formation of triiodide and pentaiodide. In situ SAXS/WAXS indicates remarkable amounts of solid iodine deposited in the carbon nanopores. Combined with stochastic modeling, in situ SAXS allows quantifying the solid iodine volume fraction and visualizing the iodine structure on 3D lattice models at the sub-nanometer scale. Based on the derived mechanism, we demonstrate strategies for improved iodine pore filling capacity and prevention of self-discharge, applicable to hybrid supercapacitors and batteries.
AU - Prehal, Christian
AU - Fitzek, Harald
AU - Kothleitner, Gerald
AU - Presser, Volker
AU - Gollas, Bernhard
AU - Freunberger, Stefan Alexander
AU - Abbas, Qamar
ID - 8568
JF - Nature Communications
KW - General Biochemistry
KW - Genetics and Molecular Biology
KW - General Physics and Astronomy
KW - General Chemistry
SN - 2041-1723
TI - Persistent and reversible solid iodine electrodeposition in nanoporous carbons
VL - 11
ER -
TY - JOUR
AB - The goal of limiting global warming to 1.5 °C requires a drastic reduction in CO2 emissions across many sectors of the world economy. Batteries are vital to this endeavor, whether used in electric vehicles, to store renewable electricity, or in aviation. Present lithium-ion technologies are preparing the public for this inevitable change, but their maximum theoretical specific capacity presents a limitation. Their high cost is another concern for commercial viability. Metal–air batteries have the highest theoretical energy density of all possible secondary battery technologies and could yield step changes in energy storage, if their practical difficulties could be overcome. The scope of this review is to provide an objective, comprehensive, and authoritative assessment of the intensive work invested in nonaqueous rechargeable metal–air batteries over the past few years, which identified the key problems and guides directions to solve them. We focus primarily on the challenges and outlook for Li–O2 cells but include Na–O2, K–O2, and Mg–O2 cells for comparison. Our review highlights the interdisciplinary nature of this field that involves a combination of materials chemistry, electrochemistry, computation, microscopy, spectroscopy, and surface science. The mechanisms of O2 reduction and evolution are considered in the light of recent findings, along with developments in positive and negative electrodes, electrolytes, electrocatalysis on surfaces and in solution, and the degradative effect of singlet oxygen, which is typically formed in Li–O2 cells.
AU - Kwak, WJ
AU - Sharon, D
AU - Xia, C
AU - Kim, H
AU - Johnson, LR
AU - Bruce, PG
AU - Nazar, LF
AU - Sun, YK
AU - Frimer, AA
AU - Noked, M
AU - Freunberger, Stefan Alexander
AU - Aurbach, D
ID - 7985
IS - 14
JF - Chemical Reviews
SN - 0009-2665
TI - Lithium-oxygen batteries and related systems: Potential, status, and future
VL - 120
ER -
TY - JOUR
AB - Water-in-salt electrolytes based on highly concentrated bis(trifluoromethyl)sulfonimide (TFSI) promise aqueous electrolytes with stabilities approaching 3 V. However, especially with an electrode approaching the cathodic (reductive) stability, cycling stability is insufficient. While stability critically relies on a solid electrolyte interphase (SEI), the mechanism behind the cathodic stability limit remains unclear. Here, we reveal two distinct reduction potentials for the chemical environments of ‘free’ and ‘bound’ water and that both contribute to SEI formation. Free-water is reduced ~1V above bound water in a hydrogen evolution reaction (HER) and responsible for SEI formation via reactive intermediates of the HER; concurrent LiTFSI precipitation/dissolution establishes a dynamic interface. The free-water population emerges, therefore, as the handle to extend the cathodic limit of aqueous electrolytes and the battery cycling stability.
AU - Bouchal, Roza
AU - Li, Zhujie
AU - Bongu, Chandra
AU - Le Vot, Steven
AU - Berthelot, Romain
AU - Rotenberg, Benjamin
AU - Favier, Frederic
AU - Freunberger, Stefan Alexander
AU - Salanne, Mathieu
AU - Fontaine, Olivier
ID - 8057
IS - 37
JF - Angewandte Chemie
SN - 0044-8249
TI - Competitive salt precipitation/dissolution during free‐water reduction in water‐in‐salt electrolyte
VL - 132
ER -
TY - JOUR
AB - Water-in-salt electrolytes based on highly concentrated bis(trifluoromethyl)sulfonimide (TFSI) promise aqueous electrolytes with stabilities nearing 3 V. However, especially with an electrode approaching the cathodic (reductive) stability, cycling stability is insufficient. While stability critically relies on a solid electrolyte interphase (SEI), the mechanism behind the cathodic stability limit remains unclear. Here, we reveal two distinct reduction potentials for the chemical environments of 'free' and 'bound' water and that both contribute to SEI formation. Free-water is reduced ~1V above bound water in a hydrogen evolution reaction (HER) and responsible for SEI formation via reactive intermediates of the HER; concurrent LiTFSI precipitation/dissolution establishes a dynamic interface. The free-water population emerges, therefore, as the handle to extend the cathodic limit of aqueous electrolytes and the battery cycling stability.
AU - Bouchal, Roza
AU - Li, Zhujie
AU - Bongu, Chandra
AU - Le Vot, Steven
AU - Berthelot, Romain
AU - Rotenberg, Benjamin
AU - Favier, Fréderic
AU - Freunberger, Stefan Alexander
AU - Salanne, Mathieu
AU - Fontaine, Olivier
ID - 7847
IS - 37
JF - Angewandte Chemie International Edition
SN - 1433-7851
TI - Competitive salt precipitation/dissolution during free‐water reduction in water‐in‐salt electrolyte
VL - 59
ER -
TY - JOUR
AB - We show the synthesis of a redox‐active quinone, 2‐methoxy‐1,4‐hydroquinone (MHQ), from a bio‐based feedstock and its suitability as electrolyte in aqueous redox flow batteries. We identified semiquinone intermediates at insufficiently low pH and quinoid radicals as responsible for decomposition of MHQ under electrochemical conditions. Both can be avoided and/or stabilized, respectively, using H 3 PO 4 electrolyte, allowing for reversible cycling in a redox flow battery for hundreds of cycles.
AU - Schlemmer, Werner
AU - Nothdurft, Philipp
AU - Petzold, Alina
AU - Frühwirt, Philipp
AU - Schmallegger, Max
AU - Gescheidt-Demner, Georg
AU - Fischer, Roland
AU - Freunberger, Stefan Alexander
AU - Kern, Wolfgang
AU - Spirk, Stefan
ID - 8329
IS - 51
JF - Angewandte Chemie International Edition
SN - 1433-7851
TI - 2‐methoxyhydroquinone from vanillin for aqueous redox‐flow batteries
VL - 59
ER -
TY - GEN
AB - PADREV : 4,4'-dimethoxy[1,1'-biphenyl]-2,2',5,5'-tetrol
Space Group: C 2 (5), Cell: a 24.488(16)Å b 5.981(4)Å c 3.911(3)Å, α 90° β 91.47(3)° γ 90°
AU - Schlemmer, Werner
AU - Nothdurft, Philipp
AU - Petzold, Alina
AU - Riess, Gisbert
AU - Frühwirt, Philipp
AU - Schmallegger, Max
AU - Gescheidt-Demner, Georg
AU - Fischer, Roland
AU - Freunberger, Stefan Alexander
AU - Kern, Wolfgang
AU - Spirk, Stefan
ID - 9780
TI - CCDC 1991959: Experimental Crystal Structure Determination
ER -
TY - JOUR
AB - Aprotic alkali metal–oxygen batteries require reversible formation of metal superoxide or peroxide on cycling. Severe parasitic reactions cause poor rechargeability, efficiency, and cycle life and have been shown to be caused by singlet oxygen (1O2) that forms at all stages of cycling. However, its formation mechanism remains unclear. We show that disproportionation of superoxide, the product or intermediate on discharge and charge, to peroxide and oxygen is responsible for 1O2 formation. While the overall reaction is driven by the stability of peroxide and thus favored by stronger Lewis acidic cations such as Li+, the 1O2 fraction is enhanced by weak Lewis acids such as organic cations. Concurrently, the metal peroxide yield drops with increasing 1O2. The results explain a major parasitic pathway during cell cycling and the growing severity in K–, Na–, and Li–O2 cells based on the growing propensity for disproportionation. High capacities and rates with peroxides are now realized to require solution processes, which form peroxide or release O2via disproportionation. The results therefore establish the central dilemma that disproportionation is required for high capacity but also responsible for irreversible reactions. Highly reversible cell operation requires hence finding reaction routes that avoid disproportionation.
AU - Mourad, Eléonore
AU - Petit, Yann K.
AU - Spezia, Riccardo
AU - Samojlov, Aleksej
AU - Summa, Francesco F.
AU - Prehal, Christian
AU - Leypold, Christian
AU - Mahne, Nika
AU - Slugovc, Christian
AU - Fontaine, Olivier
AU - Brutti, Sergio
AU - Freunberger, Stefan Alexander
ID - 7275
IS - 8
JF - Energy & Environmental Science
SN - 1754-5692
TI - Singlet oxygen from cation driven superoxide disproportionation and consequences for aprotic metal–O2 batteries
VL - 12
ER -
TY - JOUR
AB - Non-aqueous lithium-oxygen batteries cycle by forming lithium peroxide during discharge and oxidizing it during recharge. The significant problem of oxidizing the solid insulating lithium peroxide can greatly be facilitated by incorporating redox mediators that shuttle electron-holes between the porous substrate and lithium peroxide. Redox mediator stability is thus key for energy efficiency, reversibility, and cycle life. However, the gradual deactivation of redox mediators during repeated cycling has not conclusively been explained. Here, we show that organic redox mediators are predominantly decomposed by singlet oxygen that forms during cycling. Their reaction with superoxide, previously assumed to mainly trigger their degradation, peroxide, and dioxygen, is orders of magnitude slower in comparison. The reduced form of the mediator is markedly more reactive towards singlet oxygen than the oxidized form, from which we derive reaction mechanisms supported by density functional theory calculations. Redox mediators must thus be designed for stability against singlet oxygen.
AU - Kwak, Won-Jin
AU - Kim, Hun
AU - Petit, Yann K.
AU - Leypold, Christian
AU - Nguyen, Trung Thien
AU - Mahne, Nika
AU - Redfern, Paul
AU - Curtiss, Larry A.
AU - Jung, Hun-Gi
AU - Borisov, Sergey M.
AU - Freunberger, Stefan Alexander
AU - Sun, Yang-Kook
ID - 7280
JF - Nature Communications
SN - 2041-1723
TI - Deactivation of redox mediators in lithium-oxygen batteries by singlet oxygen
VL - 10
ER -
TY - JOUR
AB - Singlet oxygen (1O2) causes a major fraction of the parasitic chemistry during the cycling of non‐aqueous alkali metal‐O2 batteries and also contributes to interfacial reactivity of transition‐metal oxide intercalation compounds. We introduce DABCOnium, the mono alkylated form of 1,4‐diazabicyclo[2.2.2]octane (DABCO), as an efficient 1O2 quencher with an unusually high oxidative stability of ca. 4.2 V vs. Li/Li+. Previous quenchers are strongly Lewis basic amines with too low oxidative stability. DABCOnium is an ionic liquid, non‐volatile, highly soluble in the electrolyte, stable against superoxide and peroxide, and compatible with lithium metal. The electrochemical stability covers the required range for metal–O2 batteries and greatly reduces 1O2 related parasitic chemistry as demonstrated for the Li–O2 cell.
AU - Petit, Yann K.
AU - Leypold, Christian
AU - Mahne, Nika
AU - Mourad, Eléonore
AU - Schafzahl, Lukas
AU - Slugovc, Christian
AU - Borisov, Sergey M.
AU - Freunberger, Stefan Alexander
ID - 7276
IS - 20
JF - Angewandte Chemie International Edition
SN - 1433-7851
TI - DABCOnium: An efficient and high-voltage stable singlet oxygen quencher for metal-O2 cells
VL - 58
ER -
TY - JOUR
AB - Li–O2 batteries are plagued by side reactions that cause poor rechargeability and efficiency. These reactions were recently revealed to be predominantly caused by singlet oxygen, which can be neutralized by chemical traps or physical quenchers. However, traps are irreversibly consumed and thus only active for a limited time, and so far identified quenchers lack oxidative stability to be suitable for typically required recharge potentials. Thus, reducing the charge potential within the stability limit of the quencher and/or finding more stable quenchers is required. Here, we show that dimethylphenazine as a redox mediator decreases the charge potential well within the stability limit of the quencher 1,4-diazabicyclo[2.2.2]octane. The quencher can thus mitigate the parasitic reactions without being oxidatively decomposed. At the same time the quencher protects the redox mediator from singlet oxygen attack. The mutual conservation of the redox mediator and the quencher is rational for stable and effective Li–O2 batteries.
AU - Kwak, Won-Jin
AU - Freunberger, Stefan Alexander
AU - Kim, Hun
AU - Park, Jiwon
AU - Nguyen, Trung Thien
AU - Jung, Hun-Gi
AU - Byon, Hye Ryung
AU - Sun, Yang-Kook
ID - 7281
IS - 11
JF - ACS Catalysis
SN - 2155-5435
TI - Mutual conservation of redox mediator and singlet oxygen quencher in Lithium–Oxygen batteries
VL - 9
ER -
TY - JOUR
AB - Interphases that form on the anode surface of lithium-ion batteries are critical for performance and lifetime, but are poorly understood. Now, a decade-old misconception regarding a main component of the interphase has been revealed, which could potentially lead to improved devices.
AU - Freunberger, Stefan Alexander
ID - 7282
IS - 9
JF - Nature Chemistry
SN - 1755-4330
TI - Interphase identity crisis
VL - 11
ER -
TY - JOUR
AB - Potassium–air batteries, which suffer from oxygen cathode and potassium metal anode degradation, can be cycled thousands of times when an organic anode replaces the metal.
AU - Petit, Yann K.
AU - Freunberger, Stefan Alexander
ID - 7283
IS - 4
JF - Nature Materials
SN - 1476-1122
TI - Thousands of cycles
VL - 18
ER -
TY - JOUR
AB - In this issue of Joule, Dongmin Im and coworkers from Samsung in South Korea describe a prototype lithium-O2 battery that reaches ∼700 Wh kg–1 and ∼600 Wh L–1 on the cell level. They cut all components to the minimum to reach this value. Difficulties filling the pores with discharge product and inhomogeneous cell utilization turn out to limit the achievable energy. Their work underlines the importance of reporting performance with respect to full cell weight and volume.
AU - Prehal, Christian
AU - Freunberger, Stefan Alexander
ID - 7284
IS - 2
JF - Joule
SN - 2542-4351
TI - Li-O2 cell-scale energy densities
VL - 3
ER -
TY - GEN
AB - Electrodepositing insulating and insoluble Li2O2 is the key process during discharge of aprotic Li-O2 batteries and determines rate, capacity, and reversibility. Current understanding states that the partition between surface adsorbed and solvated LiO2 governs whether Li2O2 grows as surface film, leading to low capacity even at low rates, or in solution, leading to particles and high capacities. Here we show that Li2O2 forms to the widest extent as particles via solution mediated LiO2 disproportionation. We describe a unified Li2O2 growth model that conclusively explains capacity limitations across the whole range of electrolytes. Deciding for particle morphology, achievable rate and capacities are species mobilities, electrode specific surface area (determining true areal rate) and the concentration distribution of associated LiO2 in solution. Provided that species mobilities and surface are high, high, capacities are possible even with low-donor-number electrolytes, previously considered prototypical for low capacity via surface growth. The tools for these insights are microscopy, hydrodynamic voltammetry, a numerical reaction model, and in situ small/wide angle X-ray scattering (SAXS/WAXS). Combined with sophisticated data analysis, SAXS allows retrieving rich quantitative information from complex multi-phase systems. On a wider perspective, this SAXS method is a powerful in situ metrology with atomic to sub-micron resolution to study mechanisms in complex electrochemical systems and beyond.
AU - Prehal, Christian
AU - Samojlov, Aleksej
AU - Nachtnebel, Manfred
AU - Kriechbaum, Manfred
AU - Amenitsch, Heinz
AU - Freunberger, Stefan Alexander
ID - 7627
TI - A revised O2 reduction model in Li-O2 batteries as revealed by in situ small angle X-ray scattering
ER -
TY - JOUR
AB - Solid alkali metal carbonates are universal passivation layer components of intercalation battery materials and common side products in metal‐O2 batteries, and are believed to form and decompose reversibly in metal‐O2/CO2 cells. In these cathodes, Li2CO3 decomposes to CO2 when exposed to potentials above 3.8 V vs. Li/Li+. However, O2 evolution, as would be expected according to the decomposition reaction 2 Li2CO3→4 Li++4 e−+2 CO2+O2, is not detected. O atoms are thus unaccounted for, which was previously ascribed to unidentified parasitic reactions. Here, we show that highly reactive singlet oxygen (1O2) forms upon oxidizing Li2CO3 in an aprotic electrolyte and therefore does not evolve as O2. These results have substantial implications for the long‐term cyclability of batteries: they underpin the importance of avoiding 1O2 in metal‐O2 batteries, question the possibility of a reversible metal‐O2/CO2 battery based on a carbonate discharge product, and help explain the interfacial reactivity of transition‐metal cathodes with residual Li2CO3.
AU - Mahne, Nika
AU - Renfrew, Sara E.
AU - McCloskey, Bryan D.
AU - Freunberger, Stefan Alexander
ID - 7277
IS - 19
JF - Angewandte Chemie International Edition
SN - 1433-7851
TI - Electrochemical oxidation of Lithium Carbonate generates singlet oxygen
VL - 57
ER -
TY - JOUR
AB - Passivation layers on electrode materials are ubiquitous in nonaqueous battery chemistries and strongly govern performance and lifetime. They comprise breakdown products of the electrolyte including carbonate, alkyl carbonates, alkoxides, carboxylates, and polymers. Parasitic chemistry in metal–O2 batteries forms similar products and is tied to the deviation of the O2 balance from the ideal stoichiometry during formation/decomposition of alkaline peroxides or superoxides. Accurate and integral quantification of carbonaceous species and peroxides or superoxides in battery electrodes remains, however, elusive. We present a refined procedure to quantify them accurately and sensitively by pointing out and rectifying pitfalls of previous procedures. Carbonaceous compounds are differentiated into inorganic and organic ones. We combine mass and UV–vis spectrometry to quantify evolved O2 and complexed peroxide and CO2 evolved from carbonaceous compounds by acid treatment and Fenton’s reaction. The capabilities of the method are exemplified by means of Li–O2 and Na–O2 cathodes, graphite anodes, and LiNi0.8Co0.15Al0.05O2 cathodes.
AU - Schafzahl, Bettina
AU - Mourad, Eléonore
AU - Schafzahl, Lukas
AU - Petit, Yann K.
AU - Raju, Anjana R.
AU - Thotiyl, Musthafa Ottakam
AU - Wilkening, Martin
AU - Slugovc, Christian
AU - Freunberger, Stefan Alexander
ID - 7287
IS - 1
JF - ACS Energy Letters
SN - 2380-8195
TI - Quantifying total superoxide, peroxide, and carbonaceous compounds in metal–O2 batteries and the solid electrolyte interphase
VL - 3
ER -
TY - JOUR
AB - Hydrogelation, the self-assembly of molecules into soft, water-loaded networks, is one way to bridge the structural gap between single molecules and functional materials. The potential of hydrogels, such as those based on perylene bisimides, lies in their chemical, physical, optical, and electronic properties, which are governed by the supramolecular structure of the gel. However, the structural motifs and their precise role for long-range conductivity are yet to be explored. Here, we present a comprehensive structural picture of a perylene bisimide hydrogel, suggesting that its long-range conductivity is limited by charge transfer between electronic backbones. We reveal nanocrystalline ribbon-like structures as the electronic and structural backbone units between which charge transfer is mediated by polar solvent bridges. We exemplify this effect with sensing, where exposure to polar vapor enhances conductivity by 5 orders of magnitude, emphasizing the crucial role of the interplay between structural motif and surrounding medium for the rational design of devices based on nanocrystalline hydrogels.
AU - Burian, Max
AU - Rigodanza, Francesco
AU - Demitri, Nicola
AU - D̵ord̵ević, Luka
AU - Marchesan, Silvia
AU - Steinhartova, Tereza
AU - Letofsky-Papst, Ilse
AU - Khalakhan, Ivan
AU - Mourad, Eléonore
AU - Freunberger, Stefan Alexander
AU - Amenitsch, Heinz
AU - Prato, Maurizio
AU - Syrgiannis, Zois
ID - 7285
IS - 6
JF - ACS Nano
SN - 1936-0851
TI - Inter-backbone charge transfer as prerequisite for long-range conductivity in perylene bisimide hydrogels
VL - 12
ER -
TY - JOUR
AB - The solid electrolyte interphase (SEI) in Li and Na ion batteries forms when highly reducing or oxidizing electrode materials come into contact with a liquid organic electrolyte. Its ability to form a mechanically robust, ion-conducting, and electron-insulating layer critically determines performance, cycle life, and safety. Li or Na alkyl carbonates (LiAC and NaAC, respectively) are lead SEI components in state-of-the-art carbonate based electrolytes, and our fundamental understanding of their charge transport and mechanical properties may hold the key to designing electrolytes forming an improved SEI. We synthesized a homologous series of LiACs and NaACs from methyl to octyl analogues and characterized them with respect to structure, ionic conductivity, and stiffness. The compounds assume layered structures except for the lithium methyl carbonate. Room-temperature conductivities were found to be ∼10–9 S cm–1 for lithium methyl carbonate, <10–12 S cm–1 for the other LiACs, and <10–12 S cm–1 for the NaACs with ion transport mostly attributed to grain boundaries. While LiACs show stiffnesses of ∼1 GPa, NaACs become significantly softer with increasing chain lengths. These findings will help to more precisely interpret the complex results from charge transport and mechanical characterization of real SEIs and can give a rationale for influencing the SEI’s mechanical properties via the electrolyte.
AU - Schafzahl, Lukas
AU - Ehmann, Heike
AU - Kriechbaum, Manfred
AU - Sattelkow, Jürgen
AU - Ganner, Thomas
AU - Plank, Harald
AU - Wilkening, Martin
AU - Freunberger, Stefan Alexander
ID - 7286
IS - 10
JF - Chemistry of Materials
SN - 0897-4756
TI - Long-chain Li and Na alkyl carbonates as solid electrolyte interphase components: Structure, ion transport, and mechanical properties
VL - 30
ER -
TY - JOUR
AB - Feste Alkalicarbonate sind universelle Bestandteile von Passivierungsschichten an Materialien für Interkalationsbatterien, übliche Nebenprodukte in Metall‐O2‐Batterien, und es wird angenommen, dass sie sich reversibel in Metall‐O2 /CO2‐Zellen bilden und zersetzen. In all diesen Kathoden zersetzt sich Li2CO3 zu CO2, sobald es Spannungen >3.8 V vs. Li/Li+ ausgesetzt wird. Beachtenswert ist, dass keine O2‐Entwicklung detektiert wird, wie gemäß der Zersetzungsreaktion 2 Li2CO3 → 4 Li+ + 4 e− + 2 CO2 + O2 zu erwarten wäre. Deswegen war der Verbleib eines der O‐Atome ungeklärt und wurde nicht identifizierten parasitären Reaktionen zugerechnet. Hier zeigen wir, dass hochreaktiver Singulett‐Sauerstoff (1O2) bei der Oxidation von Li2CO3 in einem aprotischen Elektrolyten gebildet und daher nicht als O2 freigesetzt wird. Diese Ergebnisse haben weitreichende Auswirkungen auf die langfristige Zyklisierbarkeit von Batterien: sie untermauern die Wichtigkeit, 1O2 in Metall‐O2‐Batterien zu verhindern, stellen die Möglichkeit einer reversiblen Metall‐O2 /CO2‐Batterie basierend auf einem Carbonat‐Entladeprodukt in Frage und helfen, Grenzflächenreaktivität von Übergangsmetallkathoden mit Li2CO3‐Resten zu erklären.
AU - Mahne, Nika
AU - Renfrew, Sara E.
AU - McCloskey, Bryan D.
AU - Freunberger, Stefan Alexander
ID - 7983
IS - 19
JF - Angewandte Chemie
SN - 0044-8249
TI - Elektrochemische Oxidation von Lithiumcarbonat generiert Singulett-Sauerstoff
VL - 130
ER -
TY - JOUR
AB - Aprotic sodium–O2 batteries require the reversible formation/dissolution of sodium superoxide (NaO2) on cycling. Poor cycle life has been associated with parasitic chemistry caused by the reactivity of electrolyte and electrode with NaO2, a strong nucleophile and base. Its reactivity can, however, not consistently explain the side reactions and irreversibility. Herein we show that singlet oxygen (1O2) forms at all stages of cycling and that it is a main driver for parasitic chemistry. It was detected in‐ and ex‐situ via a 1O2 trap that selectively and rapidly forms a stable adduct with 1O2. The 1O2 formation mechanism involves proton‐mediated superoxide disproportionation on discharge, rest, and charge below ca. 3.3 V, and direct electrochemical 1O2 evolution above ca. 3.3 V. Trace water, which is needed for high capacities also drives parasitic chemistry. Controlling the highly reactive singlet oxygen is thus crucial for achieving highly reversible cell operation.
AU - Schafzahl, Lukas
AU - Mahne, Nika
AU - Schafzahl, Bettina
AU - Wilkening, Martin
AU - Slugovc, Christian
AU - Borisov, Sergey M.
AU - Freunberger, Stefan Alexander
ID - 7289
IS - 49
JF - Angewandte Chemie International Edition
SN - 1433-7851
TI - Singlet oxygen during cycling of the aprotic sodium-O2 battery
VL - 56
ER -
TY - JOUR
AB - Nowadays commercial supercapacitors are based on purely capacitive storage at the porous carbons that are used for the electrodes. However, the limits that capacitive storage imposes on energy density calls to investigate new materials to improve the capacitance of the device. This new type of electrodes (e.g., RuO2, MnO2…) involves pseudo-capacitive faradaic redox processes with the solid material. Ion exchange with solid materials is, however, much slower than the adsorption process in capacitive storage and inevitably leads to significant loss of power. Faradaic process in the liquid state, in contrast can be similarly fast as capacitive processes due to the fast ion transport. Designing new devices with liquid like dynamics and improved specific capacitance is challenging. We present a new approach to increase the specific capacitance using biredox ionic liquids, where redox moieties are tethered to the electrolyte ions, allowing high redox concentrations and significant pseudo-capacitive storage in the liquid state. Anions and cations are functionalized with anthraquinone (AQ) and 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) moieties, respectively. Glassy carbon, carbon-onion, and commercial activated carbon electrodes that exhibit different double layer structures and thus different diffusion dynamics were used to simultaneously study the electrochemical response of biredox ionic liquids at the positive and negative electrode.
AU - Bodin, C.
AU - Mourad, E.
AU - Zigah, D.
AU - Le Vot, S.
AU - Freunberger, Stefan Alexander
AU - Favier, F.
AU - Fontaine, O.
ID - 7288
JF - Faraday Discussions
SN - 1359-6640
TI - Biredox ionic liquids: New opportunities toward high performance supercapacitors
VL - 206
ER -
TY - JOUR
AB - We report a family of Pt and Pd benzoporphyrin dyes with versatile photophysical properties and easy access from cheap and abundant chemicals. Attaching 4 or 8 alkylsulfone groups onto a meso-tetraphenyltetrabenzoporphyrin (TPTBP) macrocylcle renders the dyes highly soluble in organic solvents, photostable, and electron-deficient with the redox potential raised up to 0.65 V versus the parent porphyrin. The new dyes intensively absorb in the blue (Soret band, 440–480 nm) and in the red (Q-band, 620–650 nm) parts of the electromagnetic spectrum and show bright phosphorescence at room-temperature in the NIR with quantum yields up to 30% in solution. The small singlet–triplet energy gap yields unusually efficient thermally activated delayed fluorescence (TADF) at elevated temperatures in solution and in polymeric matrices with quantum yields as high as 27% at 120 °C, which is remarkable for benzoporphyrins. Apart from oxygen sensing, these properties enable unprecedented simultaneous, self-referenced oxygen and temperature sensing with a single indicator dye: whereas oxygen can be determined either via the decay time of phosphorescence or TADF, the temperature is accessed via the ratio of the two emissions. Moreover, the dyes are efficient sensitizers for triplet–triplet annihilation (TTA)-based upconversion making possible longer sensitization wavelength than the conventional benzoporphyrin complexes. The Pt-octa-sulfone dye also features interesting semireversible transformation in basic media, which generates new NIR absorbing species.
AU - Zach, Peter W.
AU - Freunberger, Stefan Alexander
AU - Klimant, Ingo
AU - Borisov, Sergey M.
ID - 7290
IS - 43
JF - ACS Applied Materials & Interfaces
SN - 1944-8244
TI - Electron-deficient near-infrared Pt(II) and Pd(II) benzoporphyrins with dual phosphorescence and unusually efficient thermally activated delayed fluorescence: First demonstration of simultaneous oxygen and temperature sensing with a single emitter
VL - 9
ER -
TY - JOUR
AB - Rechargeable Li–O2 batteries have amongst the highest formal energy and could store significantly more energy than other rechargeable batteries in practice if at least a large part of their promise could be realized. Realization, however, still faces many challenges than can only be overcome by fundamental understanding of the processes taking place. Here, we review recent advances in understanding the chemistry of the Li–O2 cathode and provide a perspective on dominant research needs. We put particular emphasis on issues that are often grossly misunderstood: realistic performance metrics and their reporting as well as identifying reversibility and quantitative measures to do so. Parasitic reactions are the prime obstacle for reversible cell operation and have recently been identified to be predominantly caused by singlet oxygen and not by reduced oxygen species as thought before. We discuss the far reaching implications of this finding on electrolyte and cathode stability, electrocatalysis, and future research needs.
AU - Mahne, Nika
AU - Fontaine, Olivier
AU - Thotiyl, Musthafa Ottakam
AU - Wilkening, Martin
AU - Freunberger, Stefan Alexander
ID - 7292
IS - 10
JF - Chemical Science
SN - 2041-6520
TI - Mechanism and performance of lithium–oxygen batteries – a perspective
VL - 8
ER -
TY - JOUR
AB - Na battery chemistries show poor passivation behavior of low voltage Na storage compounds and Na metal with organic carbonate‐based electrolytes adopted from Li‐ion batteries. Therefore, a suitable electrolyte remains a major challenge for establishing Na batteries. Here we report highly concentrated sodium bis(fluorosulfonyl)imide (NaFSI) in dimethoxyethane (DME) electrolytes and investigate them for Na metal and hard carbon anodes and intercalation cathodes. For a DME/NaFSI ratio of 2, a stable passivation of anode materials was found owing to the formation of a stable solid electrolyte interface, which was characterized spectroscopically. This permitted non‐dentritic Na metal cycling with approximately 98 % coulombic efficiency as shown for up to 300 cycles. The NaFSI/DME electrolyte may enable Na‐metal anodes and allows for more reliable assessment of electrode materials in Na‐ion half‐cells, as is demonstrated by comparing half‐cell cycling of hard carbon anodes and Na3V2(PO4)3 cathodes with a widely used carbonate and the NaFSI/DME electrolyte.
AU - Schafzahl, Lukas
AU - Hanzu, Ilie
AU - Wilkening, Martin
AU - Freunberger, Stefan Alexander
ID - 7291
IS - 2
JF - ChemSusChem
SN - 1864-5631
TI - An electrolyte for reversible cycling of sodium metal and intercalation compounds
VL - 10
ER -
TY - JOUR
AB - Aprotische Natrium‐O2‐Batterien basieren auf der reversiblen Bildung und Auflösung von Natriumsuperoxid (NaO2) während des Zellbetriebs. Nebenreaktionen des Elektrolyten und der Elektrode mit dem stark nukleophilen und basischen NaO2 führen zu mangelhafter Zyklenstabilität. Seine Reaktivität allein kann die Nebenreaktionen und schlechte Reversibilität jedoch nicht schlüssig erklären. Hier wird gezeigt, dass Singulett‐Sauerstoff (1O2) in allen Phasen des Betriebs entsteht und eine Hauptursache für Nebenreaktionen ist. 1O2 wurde in situ und ex situ mit einem 1O2‐Fänger detektiert, der schnell und selektiv ein Addukt mit 1O2 bildet. Mechanistisch betrachtet entsteht 1O2 entweder durch protonenunterstützte Disproportionierung von Superoxid während des Entladens, Lagerns und Ladens unter ca. 3.3 V oder durch direkte elektrochemische 1O2‐Entwicklung über ca. 3.3 V. Spuren von Wasser ermöglichen hohe Kapazitäten, beschleunigen aber auch Nebenreaktionen. Daher muss das hochreaktive 1O2 unbedingt kontrolliert werden, um die Zelle reversibel zu betreiben.
AU - Schafzahl, Lukas
AU - Mahne, Nika
AU - Schafzahl, Bettina
AU - Wilkening, Martin
AU - Slugovc, Christian
AU - Borisov, Sergey M.
AU - Freunberger, Stefan Alexander
ID - 7981
IS - 49
JF - Angewandte Chemie
SN - 0044-8249
TI - Singulett-Sauerstoff in der aprotischen Natrium-O2-Batterie
VL - 129
ER -
TY - CHAP
AB - In this part, the use of polysaccharides, either directly through composite approaches, or by carbonization will be described. In many cases, materials are obtained which are competitive in terms of capacitance and cycle lifetime. In this part, the use of polysaccharides, either directly through composite approaches, or by carbonization will be described. In many cases, materials are obtained which are competitive in terms of capacitance and cycle lifetime. The following part will focus mainly on cellulosic composites with conductive polymers since cellulose is most abundant and therefore has attracted much more research interest in this field whereas in the second part also other polysaccharides, such as chitin, xylans, alginates, pectins, dextrans and caragenaans have been used in carbonization experiments.
AU - Yee Liew, Soon
AU - Thielemans, Wim
AU - Freunberger, Stefan Alexander
AU - Spirk, Stefan
ED - Yee Liew, Soon
ED - Thielemans, Wim
ED - Freunberger, Stefan Alexander
ED - Spirk, Stefan
ID - 7980
SN - 2191-5407
T2 - Polysaccharide Based Supercapacitors
TI - Polysaccharides in supercapacitors
ER -
TY - JOUR
AB - Beyond-intercalation batteries promise a step-change in energy storage compared to intercalation-based lithium-ion and sodium-ion batteries. However, only performance metrics that include all cell components and operation parameters can tell whether a true advance over intercalation batteries has been achieved.
AU - Freunberger, Stefan Alexander
ID - 7982
IS - 7
JF - Nature Energy
SN - 2058-7546
TI - True performance metrics in beyond-intercalation batteries
VL - 2
ER -
TY - JOUR
AU - Mahne, Nika
AU - Schafzahl, Bettina
AU - Leypold, Christian
AU - Leypold, Mario
AU - Grumm, Sandra
AU - Leitgeb, Anita
AU - Strohmeier, Gernot A.
AU - Wilkening, Martin
AU - Fontaine, Olivier
AU - Kramer, Denis
AU - Slugovc, Christian
AU - Borisov, Sergey M.
AU - Freunberger, Stefan Alexander
ID - 7986
IS - 5
JF - Nature Energy
SN - 2058-7546
TI - Singlet oxygen generation as a major cause for parasitic reactions during cycling of aprotic lithium–oxygen batteries
VL - 2
ER -
TY - JOUR
AB - Kinetics of electrochemical reactions are several orders of magnitude slower in solids than in liquids as a result of the much lower ion diffusivity. Yet, the solid state maximizes the density of redox species, which is at least two orders of magnitude lower in liquids because of solubility limitations. With regard to electrochemical energy storage devices, this leads to high-energy batteries with limited power and high-power supercapacitors with a well-known energy deficiency. For such devices the ideal system should endow the liquid state with a density of redox species close to the solid state. Here we report an approach based on biredox ionic liquids to achieve bulk-like redox density at liquid-like fast kinetics. The cation and anion of these biredox ionic liquids bear moieties that undergo very fast reversible redox reactions. As a first demonstration of their potential for high-capacity/high-rate charge storage, we used them in redox supercapacitors. These ionic liquids are able to decouple charge storage from an ion-accessible electrode surface, by storing significant charge in the pores of the electrodes, to minimize self-discharge and leakage current as a result of retaining the redox species in the pores, and to raise working voltage due to their wide electrochemical window.
AU - Mourad, Eléonore
AU - Coustan, Laura
AU - Lannelongue, Pierre
AU - Zigah, Dodzi
AU - Mehdi, Ahmad
AU - Vioux, André
AU - Freunberger, Stefan Alexander
AU - Favier, Frédéric
AU - Fontaine, Olivier
ID - 7279
IS - 4
JF - Nature Materials
SN - 1476-1122
TI - Biredox ionic liquids with solid-like redox density in the liquid state for high-energy supercapacitors
VL - 16
ER -
TY - JOUR
AB - Mesoporous nanocrystalline TiO2 and TiO2–V2O5 microspheres were prepared by non-hydrolytic sol–gel from TiCl4, VOCl3, and iPr2O at 110 °C without any solvent or additives. The samples were characterized by elemental analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, nitrogen physisorption, and impedance measurements. At low vanadium loadings, only TiO2 anatase was detected, and V2O5 scherbinaite was also detected at high vanadium loadings. The texture of the samples depended on the V loading, but all the samples appeared built of primary nanoparticles (≈10–20 nm in size) that aggregate to form mesoporous micron-sized spheres. The lithium insertion properties of these materials were evaluated by galvanostatic measurements taken using coin-type cells, in view of their application as electrode for rechargeable Li-ion batteries. The mesoporous TiO2 microspheres showed good performances, with a specific reversible capacity of 145 and 128 mAh g−1 at C/2 and C, respectively (C = 335.6 mA g−1), good coulombic efficiency, and a moderate capacity fade (6 %) from the 2nd to the 20th cycle at C/20. Although the addition of V effectively increased the electronic conductivity of the powders, the specific reversible capacity and cycling performances of the TiO2–V2O5 samples were only minimally improved for a 5 at% V loading and were lower at higher V loading.
AU - Escamilla-Pérez, A. M.
AU - Louvain, N.
AU - Kaschowitz, M.
AU - Freunberger, Stefan Alexander
AU - Fontaine, O.
AU - Boury, B.
AU - Brun, N.
AU - Mutin, P. H.
ID - 7294
IS - 2
JF - Journal of Sol-Gel Science and Technology
SN - 0928-0707
TI - Lithium insertion properties of mesoporous nanocrystalline TiO2 and TiO2–V2O5 microspheres prepared by non-hydrolytic sol–gel
VL - 79
ER -
TY - JOUR
AB - Within the scope of developing a multi-physical model describing battery behavior during and after the mechanical load (accelerations, intrusions) of a vehicle’s high voltage battery, an internal short circuit model is of deep interest for a virtual hazard assessment. The internal short resistance and the size of the affected area must be known as a minimum for determining the released heat and, in consequence, the temperatures. The internal short resistance of purpose-built dummy pouch cells, filled with electrolyte-like solvent without conductive salt, has thus been measured in a given short area under various compressive loads. The resistances for different short scenarios obtained are analyzed and described in a mathematical form. Short circuit experiments with dummy cells using an external power source have also been carried out. This set-up allows the measurement of the temperature evolution at a known current and a determination of the actual short resistance. The post-mortem analysis of the samples shows a correlation between the maximum temperatures, released short heat and the separator melt diameter.
AU - Volck, Theo
AU - Sinz, Wolfgang
AU - Gstrein, Gregor
AU - Breitfuss, Christoph
AU - Heindl, Simon
AU - Steffan, Hermann
AU - Freunberger, Stefan Alexander
AU - Wilkening, Martin
AU - Uitz, Marlena
AU - Fink, Clemens
AU - Geier, Alexander
ID - 7296
IS - 2
JF - Batteries
SN - 2313-0105
TI - Method for determination of the internal short resistance and heat evolution at different mechanical loads of a Lithium ion battery cell based on dummy pouch cells
VL - 2
ER -
TY - JOUR
AB - Redox ionic liquids consisting of ions bearing redox moieties are receiving increasing interest in electrochemical applications, as they associate electroactive properties with the classical properties of ionic liquids. Here, biredox ionic liquid electrolytes are described in which both anion and cation are functionalized with anthraquinone and 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) groups, respectively. In-depth investigations based on crossed experimental and theoretical studies were carried out to elucidate how the bulkiness of ions bearing a redox moiety impacted electron and mass transfers, and accordingly the efficiency of electrochemical devices. The values of solvated radii of different redox ions, as well as the related kinetic constants, were extracted from cyclic voltammetry experiments. Reformulating the basic relations of electron transfer theory (based on Marcus-Hush theory) evidenced that in such redox species, with an unsymmetrical located redox centre, the electron transfer was not governed by the overall size of the solvated redox species, but rather by the radius of the redox active subunit, which takes preferential orientation towards the surface, thus allowing higher kinetic constants than what classical theory would predict. This vision opens ample opportunities for biredox ILs as electrolytes in electrochemical devices.
AU - Mourad, Eléonore
AU - Coustan, Laura
AU - Freunberger, Stefan Alexander
AU - Mehdi, Ahmad
AU - Vioux, André
AU - Favier, Frédérique
AU - Fontaine, Olivier
ID - 7295
IS - 7
JF - Electrochimica Acta
SN - 0013-4686
TI - Biredox ionic liquids: Electrochemical investigation and impact of ion size on electron transfer
VL - 206
ER -
TY - JOUR
AB - Redox mediators facilitate the oxidation of the highly insulating discharge product in metal–oxygen batteries during recharge and offer opportunities to achieve high reversible capacities. Now a design principle for selecting redox mediators that can recharge the batteries more efficiently is suggested.
AU - Freunberger, Stefan Alexander
ID - 7297
IS - 6
JF - Nature Energy
SN - 2058-7546
TI - Batteries: Charging ahead rationally
VL - 1
ER -
TY - JOUR
AB - If proton exchange membrane fuel cells (PEMFC) are ever to succeed in sustainable energy landscape as a potential zero emission technology, it is inevitable to reduce electricity production cost associated mainly with its MEAs, cell hardware and gas storage units. We demonstrate a diverse strategy for achieving this target with a concomitant amplification of its specific energy and power, by rolling a thin graphene oxide (GO) based MEA alone into a tubular and air breathing architecture with internal fuel storage. The unique properties of GO being a barrier for molecular fuels and proton conducting to construct a GO based cylindrical MEA. This makes the tubular PEMFC ∼75 times lighter, featuring ∼37 and ∼92 times respectively, the power and energy per overall weight, making it a potential candidate for portable applications. The intrinsic electrochemical kinetics at the three-phase boundary are somewhat affected by the bending of the MEA, albeit at overall reduction in power production cost.
AU - Thimmappa, Ravikumar
AU - Chattanahalli Devendrachari, Mruthyunjayachari
AU - Shafi, Shahid
AU - Freunberger, Stefan Alexander
AU - Ottakam Thotiyl, Musthafa
ID - 7293
IS - 47
JF - International Journal of Hydrogen Energy
SN - 0360-3199
TI - Proton conducting hollow graphene oxide cylinder as molecular fuel barrier for tubular H2-air fuel cell
VL - 41
ER -
TY - JOUR
AB - Lithium-ion batteries are in widespread use in electric vehicles and hybrid vehicles. Besides features like energy density, cost, lifetime, and recyclability the safety of a battery system is of prime importance. The separator material impacts all these properties and requires therefore an informed selection. The interplay between the mechanical and electrochemical properties as key selection criteria is investigated. Mechanical properties were investigated using tensile and puncture penetration tests at abuse relevant conditions. To investigate the electrochemical performance in terms of effective conductivity a method based on impedance spectroscopy was introduced. This methodology is applied to evaluate ten commercial separators which allows for a trade-off analysis of mechanical versus electrochemical performance. Based on the results, and in combination with other factors, this offers an effective approach to select suitable separators for automotive applications.
AU - Plaimer, Martin
AU - Breitfuß, Christoph
AU - Sinz, Wolfgang
AU - Heindl, Simon F.
AU - Ellersdorfer, Christian
AU - Steffan, Hermann
AU - Wilkening, Martin
AU - Hennige, Volker
AU - Tatschl, Reinhard
AU - Geier, Alexander
AU - Schramm, Christian
AU - Freunberger, Stefan Alexander
ID - 7298
IS - 2
JF - Journal of Power Sources
SN - 0378-7753
TI - Evaluating the trade-off between mechanical and electrochemical performance of separators for lithium-ion batteries: Methodology and application
VL - 306
ER -
TY - CHAP
AB - The electrolyte in the non-aqueous (aprotic) lithium air battery has a profound influence on the reactions that occur at the anode and cathode, and hence its overall operation on discharge/charge. It must possess a wide range of attributes, exceeding the requirements of electrolytes for Lithium ion batteries by far. The most important additional issues are stability at both anode and cathode in the presence of O2. The known problems with cycling the Li metal/non-aqueous electrolyte interface are further complicated by O2. New and much less understood are the reactions at the O2 cathode/electrolyte interface where the highly reversible formation/decomposition of Li2O2 on discharge/charge is critical for the operation of the non-aqueous lithium air battery. Many aprotic electrolytes exhibit decomposition at the cathode during discharge and charge due to the presence of reactive reduced O2 species affecting potential, capacity and kinetics on discharge and charge, cyclability and calendar life. Identifying suitable electrolytes is one of the key challenges for the non-aqueous lithium air battery at the present time. Following the realisation that cyclability of such cells in the initially used organic carbonate electrolytes is due to back-to-back irreversible reactions the stability of the non-aqueous electrolytes became a major focus of research on rechargeable lithium air batteries. This realisation led to the establishment of a suite of experimental and computational methods capable of screening the stability of electrolytes. These allow for greater mechanistic understanding of the reactivity and guide the way towards designing more stable systems. A range of electrolytes based on ethers, amides, sulfones, ionic liquids and dimethyl sulfoxide have been investigated. All are more stable than the organic carbonates, but not all are equally stable. Even though it was soon realised, by a number of groups, that ethers exhibit side reactions on discharge and charge, they still remain the choice in many studies. To date dimethyl sulfoxide and dimethylacetamide were identified as the most stable electrolytes. In conjunction with the investigation of electrolyte stability the importance of electrode stability became more prominent. The stability of the electrolyte cannot be considered in isolation. Its stability depends on the synergy between electrolyte and electrode. Carbon based electrodes promote electrolyte decomposition and decompose on their own. Although great progress has been made in only a few years, future work on aprotic electrolytes for Li-O2 batteries will need to explore other electrolytes in the quest for yet lower cost, higher safety, stability and low volatility.
AU - Freunberger, Stefan Alexander
AU - Chen, Yuhui
AU - Bardé, Fanny
AU - Takechi, Kensuke
AU - Mizuno, Fuminori
AU - Bruce, Peter G.
ED - Imanishi, Nobuyuki
ED - Luntz, Alan C.
ED - Bruce, Peter
ID - 7303
SN - 9781489980618
T2 - The Lithium Air Battery: Fundamentals
TI - Nonaqueous Electrolytes
ER -
TY - JOUR
AB - Understanding charge carrier transport in Li2O2, the storage material in the non-aqueous Li-O2 battery, is key to the development of this high-energy battery. Here, we studied ionic transport properties and Li self-diffusion in nanocrystalline Li2O2 by conductivity and temperature variable 7Li NMR spectroscopy. Nanostructured Li2O2, characterized by a mean crystallite size of less than 50 nm as estimated from X-ray diffraction peak broadening, was prepared by high-energy ball milling of microcrystalline lithium peroxide with μm sized crystallites. At room temperature the overall conductivity σ of the microcrystalline reference sample turned out to be very low (3.4 × 10−13 S cm−1) which is in agreement with results from temperature-variable 7Li NMR line shape measurements. Ball-milling, however, leads to an increase of σ by approximately two orders of magnitude (1.1 × 10−10 S cm−1); correspondingly, the activation energy decreases from 0.89 eV to 0.82 eV. The electronic contribution σeon, however, is in the order of 9 × 10−12 S cm−1 which makes less than 10% of the total value. Interestingly, 7Li NMR lines of nano-Li2O2 undergo pronounced heterogeneous motional narrowing which manifests in a two-component line shape emerging with increasing temperatures. Most likely, the enhancement in σ can be traced back to the generation of a spin reservoir with highly mobile Li ions; these are expected to reside in the nearest neighbourhood of defects generated or near the structurally disordered and defect-rich interfacial regions formed during mechanical treatment.
AU - Dunst, A.
AU - Epp, V.
AU - Hanzu, I.
AU - Freunberger, Stefan Alexander
AU - Wilkening, M.
ID - 7302
IS - 8
JF - Energy & Environmental Science
SN - 1754-5692
TI - Short-range Li diffusion vs. long-range ionic conduction in nanocrystalline lithium peroxide Li2O2—the discharge product in lithium-air batteries
VL - 7
ER -
TY - JOUR
AB - When lithium–oxygen batteries discharge, O2 is reduced at the cathode to form solid Li2O2. Understanding the fundamental mechanism of O2 reduction in aprotic solvents is therefore essential to realizing their technological potential. Two different models have been proposed for Li2O2 formation, involving either solution or electrode surface routes. Here, we describe a single unified mechanism, which, unlike previous models, can explain O2 reduction across the whole range of solvents and for which the two previous models are limiting cases. We observe that the solvent influences O2 reduction through its effect on the solubility of LiO2, or, more precisely, the free energy of the reaction LiO2* ⇌ Li(sol)+ + O2−(sol) + ion pairs + higher aggregates (clusters). The unified mechanism shows that low-donor-number solvents are likely to lead to premature cell death, and that the future direction of research for lithium–oxygen batteries should focus on the search for new, stable, high-donor-number electrolytes, because they can support higher capacities and can better sustain discharge.
AU - Johnson, Lee
AU - Li, Chunmei
AU - Liu, Zheng
AU - Chen, Yuhui
AU - Freunberger, Stefan Alexander
AU - Ashok, Praveen C.
AU - Praveen, Bavishna B.
AU - Dholakia, Kishan
AU - Tarascon, Jean-Marie
AU - Bruce, Peter G.
ID - 7305
IS - 12
JF - Nature Chemistry
SN - 1755-4330
TI - The role of LiO2 solubility in O2 reduction in aprotic solvents and its consequences for Li–O2 batteries
VL - 6
ER -
TY - JOUR
AB - Lithium-air batteries have received extraordinary attention recently owing to their theoretical gravimetric energies being considerably higher than those of Li-ion batteries. There are, however, significant challenges to practical implementation, including low energy efficiency, cycle life, and power capability. These are due primarily to the lack of fundamental understanding of oxygen reduction and evolution reaction kinetics and parasitic reactions between oxygen redox intermediate species and nominally inactive battery components such as carbon in the oxygen electrode and electrolytes. In this article, we discuss recent advances in the mechanistic understanding of oxygen redox reactions in nonaqueous electrolytes and the search for electrolytes and electrode materials that are chemically stable in the oxygen electrode. In addition, methods to protect lithium metal against corrosion by water and dendrite formation in aqueous lithium-air batteries are discussed. Further materials innovations lie at the heart of research and development efforts that are needed to enable the development of lithium-oxygen batteries with enhanced round-trip efficiency and cycle life.
AU - Kwabi, D.G.
AU - Ortiz-Vitoriano, N.
AU - Freunberger, Stefan Alexander
AU - Chen, Y.
AU - Imanishi, N.
AU - Bruce, P.G.
AU - Shao-Horn, Y.
ID - 7304
IS - 5
JF - MRS Bulletin
SN - 0883-7694
TI - Materials challenges in rechargeable lithium-air batteries
VL - 39
ER -
TY - JOUR
AB - Several problems arise at the O2 (positive) electrode in the Li-air battery, including solvent/electrode decomposition and electrode passivation by insulating Li2O2. Progress partially depends on exploring the basic electrochemistry of O2 reduction. Here we describe the effect of complexing-cations on the electrochemical reduction of O2 in DMSO in the presence and absence of a Li salt. The solubility of alkaline peroxides in DMSO is enhanced by the complexing-cations, consistent with their strong interaction with reduced O2. The complexing-cations also increase the rate of the 1-electron O2 reduction to O2•– by up to six-fold (k° = 2.4 ×10–3 to 1.5 × 10–2 cm s–1) whether or not Li+ ions are present. In the absence of Li+, the complexing-cations also promote the reduction of O2•– to O22–. In the presence of Li+ and complexing-cations, and despite the interaction of the reduced O2 with the latter, SERS confirms that the product is still Li2O2.
AU - Li, Chunmei
AU - Fontaine, Olivier
AU - Freunberger, Stefan Alexander
AU - Johnson, Lee
AU - Grugeon, Sylvie
AU - Laruelle, Stéphane
AU - Bruce, Peter G.
AU - Armand, Michel
ID - 7301
IS - 7
JF - The Journal of Physical Chemistry C
SN - 1932-7447
TI - Aprotic Li–O2 battery: Influence of complexing agents on oxygen reduction in an aprotic solvent
VL - 118
ER -
TY - JOUR
AB - Photoinduced electron transfer (PET), which causes pH-dependent quenching of fluorescent dyes, is more effectively introduced by phenolic groups than by amino groups which have been much more commonly used so far. That is demonstrated by fluorescence measurements involving several classes of fluorophores. Electrochemical measurements show that PET in several amino-modified dyes is thermodynamically favorable, even though it was not experimentally found, underlining the importance of kinetic aspects to the process. Consequently, the attachment of phenolic groups allows for fast and simple preparation of a wide selection of fluorescent pH-probes with tailor-made spectral properties, sensitive ranges, and individual advantages, so that a large number of applications can be realized. Fluorophores carrying phenolic groups may also be used for sensing analytes other than pH or molecular switching and signaling.
AU - Aigner, Daniel
AU - Freunberger, Stefan Alexander
AU - Wilkening, Martin
AU - Saf, Robert
AU - Borisov, Sergey M.
AU - Klimant, Ingo
ID - 7300
IS - 18
JF - Analytical Chemistry
SN - 0003-2700
TI - Enhancing photoinduced electron transfer efficiency of fluorescent pH-probes with halogenated phenols
VL - 86
ER -
TY - JOUR
AB - Rechargeable lithium–air (O2) batteries are receiving intense interest because their high theoretical specific energy exceeds that of lithium-ion batteries. If the Li–O2 battery is ever to succeed, highly reversible formation/decomposition of Li2O2 must take place at the cathode on cycling. However, carbon, used ubiquitously as the basis of the cathode, decomposes during Li2O2 oxidation on charge and actively promotes electrolyte decomposition on cycling. Replacing carbon with a nanoporous gold cathode, when in contact with a dimethyl sulphoxide-based electrolyte, does seem to demonstrate better stability. However, nanoporous gold is not a suitable cathode; its high mass destroys the key advantage of Li–O2 over Li ion (specific energy), it is too expensive and too difficult to fabricate. Identifying a suitable cathode material for the Li–O2 cell is one of the greatest challenges at present. Here we show that a TiC-based cathode reduces greatly side reactions (arising from the electrolyte and electrode degradation) compared with carbon and exhibits better reversible formation/decomposition of Li2O2 even than nanoporous gold (>98% capacity retention after 100 cycles, compared with 95% for nanoporous gold); it is also four times lighter, of lower cost and easier to fabricate. The stability may originate from the presence of TiO2 (along with some TiOC) on the surface of TiC. In contrast to carbon or nanoporous gold, TiC seems to represent a more viable, stable, cathode for aprotic Li–O2 cells.
AU - Ottakam Thotiyl, Muhammed M.
AU - Freunberger, Stefan Alexander
AU - Peng, Zhangquan
AU - Chen, Yuhui
AU - Liu, Zheng
AU - Bruce, Peter G.
ID - 7306
IS - 11
JF - Nature Materials
SN - 1476-1122
TI - A stable cathode for the aprotic Li–O2 battery
VL - 12
ER -
TY - JOUR
AB - The non-aqueous Li–air (O2) battery is receiving intense interest because its theoretical specific energy exceeds that of Li-ion batteries. Recharging the Li–O2 battery depends on oxidizing solid lithium peroxide (Li2O2), which is formed on discharge within the porous cathode. However, transporting charge between Li2O2 particles and the solid electrode surface is at best very difficult and leads to voltage polarization on charging, even at modest rates. This is a significant problem facing the non-aqueous Li–O2 battery. Here we show that incorporation of a redox mediator, tetrathiafulvalene (TTF), enables recharging at rates that are impossible for the cell in the absence of the mediator. On charging, TTF is oxidized to TTF+ at the cathode surface; TTF+ in turn oxidizes the solid Li2O2, which results in the regeneration of TTF. The mediator acts as an electron–hole transfer agent that permits efficient oxidation of solid Li2O2. The cell with the mediator demonstrated 100 charge/discharge cycles.
AU - Chen, Yuhui
AU - Freunberger, Stefan Alexander
AU - Peng, Zhangquan
AU - Fontaine, Olivier
AU - Bruce, Peter G.
ID - 7307
IS - 6
JF - Nature Chemistry
SN - 1755-4330
TI - Charging a Li–O2 battery using a redox mediator
VL - 5
ER -
TY - JOUR
AB - Carbon has been used widely as the basis of porous cathodes for nonaqueous Li–O2 cells. However, the stability of carbon and the effect of carbon on electrolyte decomposition in such cells are complex and depend on the hydrophobicity/hydrophilicity of the carbon surface. Analyzing carbon cathodes, cycled in Li–O2 cells between 2 and 4 V, using acid treatment and Fenton’s reagent, and combined with differential electrochemical mass spectrometry and FTIR, demonstrates the following: Carbon is relatively stable below 3.5 V (vs Li/Li+) on discharge or charge, especially so for hydrophobic carbon, but is unstable on charging above 3.5 V (in the presence of Li2O2), oxidatively decomposing to form Li2CO3. Direct chemical reaction with Li2O2 accounts for only a small proportion of the total carbon decomposition on cycling. Carbon promotes electrolyte decomposition during discharge and charge in a Li–O2 cell, giving rise to Li2CO3 and Li carboxylates (DMSO and tetraglyme electrolytes). The Li2CO3 and Li carboxylates present at the end of discharge and those that form on charge result in polarization on the subsequent charge. Li2CO3 (derived from carbon and from the electrolyte) as well as the Li carboxylates (derived from the electrolyte) decompose and form on charging. Oxidation of Li2CO3 on charging to ∼4 V is incomplete; Li2CO3 accumulates on cycling resulting in electrode passivation and capacity fading. Hydrophilic carbon is less stable and more catalytically active toward electrolyte decomposition than carbon with a hydrophobic surface. If the Li–O2 cell could be charged at or below 3.5 V, then carbon may be relatively stable, however, its ability to promote electrolyte decomposition, presenting problems for its use in a practical Li–O2 battery. The results emphasize that stable cycling of Li2O2 at the cathode in a Li–O2 cell depends on the synergy between electrolyte and electrode; the stability of the electrode and the electrolyte cannot be considered in isolation.
AU - Ottakam Thotiyl, Muhammed M.
AU - Freunberger, Stefan Alexander
AU - Peng, Zhangquan
AU - Bruce, Peter G.
ID - 7308
IS - 1
JF - Journal of the American Chemical Society
SN - 0002-7863
TI - The carbon electrode in nonaqueous Li–O2 cells
VL - 135
ER -
TY - JOUR
AB - Energy‐storage technologies, including electrical double‐layer capacitors and rechargeable batteries, have attracted significant attention for applications in portable electronic devices, electric vehicles, bulk electricity storage at power stations, and “load leveling” of renewable sources, such as solar energy and wind power. Transforming lithium batteries and electric double‐layer capacitors requires a step change in the science underpinning these devices, including the discovery of new materials, new electrochemistry, and an increased understanding of the processes on which the devices depend. The Review will consider some of the current scientific issues underpinning lithium batteries and electric double‐layer capacitors.
AU - Choi, Nam-Soon
AU - Chen, Zonghai
AU - Freunberger, Stefan Alexander
AU - Ji, Xiulei
AU - Sun, Yang-Kook
AU - Amine, Khalil
AU - Yushin, Gleb
AU - Nazar, Linda F.
AU - Cho, Jaephil
AU - Bruce, Peter G.
ID - 7309
IS - 40
JF - Angewandte Chemie International Edition
SN - 1433-7851
TI - Challenges facing Lithium batteries and electrical double-layer capacitors
VL - 51
ER -
TY - JOUR
AB - The rechargeable nonaqueous lithium-air (Li-O2) battery is receiving a great deal of interest because, theoretically, its specific energy far exceeds the best that can be achieved with lithium-ion cells. Operation of the rechargeable Li-O2 battery depends critically on repeated and highly reversible formation/decomposition of lithium peroxide (Li2O2) at the cathode upon cycling. Here, we show that this process is possible with the use of a dimethyl sulfoxide electrolyte and a porous gold electrode (95% capacity retention from cycles 1 to 100), whereas previously only partial Li2O2 formation/decomposition and limited cycling could occur. Furthermore, we present data indicating that the kinetics of Li2O2 oxidation on charge is approximately 10 times faster than on carbon electrodes.
AU - Peng, Z.
AU - Freunberger, Stefan Alexander
AU - Chen, Y.
AU - Bruce, P. G.
ID - 7310
IS - 6094
JF - Science
SN - 0036-8075
TI - A reversible and higher-rate Li-O2 battery
VL - 337
ER -
TY - JOUR
AB - Stability of the electrolyte toward reduced oxygen species generated at the cathode is a crucial challenge for the rechargeable nonaqueous Li–O2 battery. Here, we investigate dimethylformamide as the basis of an electrolyte. Although reactions at the O2 cathode on the first discharge–charge cycle are dominated by reversible Li2O2 formation/decomposition, there is also electrolyte decomposition, which increases on cycling. The products of decomposition at the cathode on discharge are Li2O2, Li2CO3, HCO2Li, CH3CO2Li, NO, H2O, and CO2. Li2CO3 accumulates in the electrode with cycling. The stability of dimethylformamide toward reduced oxygen species is insufficient for its use in the rechargeable nonaqueous Li–O2 battery.
AU - Chen, Yuhui
AU - Freunberger, Stefan Alexander
AU - Peng, Zhangquan
AU - Bardé, Fanny
AU - Bruce, Peter G.
ID - 7311
IS - 18
JF - Journal of the American Chemical Society
SN - 0002-7863
TI - Li–O2 battery with a dimethylformamide electrolyte
VL - 134
ER -
TY - JOUR
AB - Li-ion batteries have transformed portable electronics and will play a key role in the electrification of transport. However, the highest energy storage possible for Li-ion batteries is insufficient for the long-term needs of society, for example, extended-range electric vehicles. To go beyond the horizon of Li-ion batteries is a formidable challenge; there are few options. Here we consider two: Li–air (O2) and Li–S. The energy that can be stored in Li–air (based on aqueous or non-aqueous electrolytes) and Li–S cells is compared with Li-ion; the operation of the cells is discussed, as are the significant hurdles that will have to be overcome if such batteries are to succeed. Fundamental scientific advances in understanding the reactions occurring in the cells as well as new materials are key to overcoming these obstacles. The potential benefits of Li–air and Li–S justify the continued research effort that will be needed.
AU - Bruce, Peter G.
AU - Freunberger, Stefan Alexander
AU - Hardwick, Laurence J.
AU - Tarascon, Jean-Marie
ID - 7313
IS - 1
JF - Nature Materials
SN - 1476-1122
TI - Li–O2 and Li–S batteries with high energy storage
VL - 11
ER -
TY - JOUR
AB - The electrolyte is one of the greatest challenges facing the development of the non‐aqueous Li–O2 battery. Although ether‐based electrolytes do from Li2O2 on the first discharge, it is shown by various techniques that they also decompose and that decomposition increases while Li2O2 decreases on cycling (see picture). Thus, these electrolytes are not suitable.
AU - Freunberger, Stefan Alexander
AU - Chen, Yuhui
AU - Drewett, Nicholas E.
AU - Hardwick, Laurence J.
AU - Bardé, Fanny
AU - Bruce, Peter G.
ID - 7314
IS - 37
JF - Angewandte Chemie International Edition
SN - 1433-7851
TI - The Lithium-Oxygen battery with ether-based electrolytes
VL - 50
ER -
TY - JOUR
AB - Lithium-metal oxides with a high formal Li2O content, such as Li5FeO4 (5Li2O•Fe2O3) and a Li2MnO3•LiFeO2 composite ({Li2O•MnO2}•{Li2O•Fe2O3}) have been explored as electrocatalysts for primary and rechargeable Li-O2 cells. Activation occurs predominantly by Li2O removal, either electrochemically or chemically by acid-treatment. Superior electrochemical behavior is obtained if activation occurs by acid-treatment; Li2MnO3•LiFeO2 catalysts provide 2516 mAh/g (carbon) corresponding to 931 mAh/g (electrocatalyst + carbon) during the initial discharge. The reaction is reasonably reversible during the early cycles. The approach has implications for designing electrocatalysts that participate through electrochemical Li2O extraction/reformation reactions, offering exceptionally high capacities.
AU - Trahey, L.
AU - Johnson, C. S.
AU - Vaughey, J. T.
AU - Kang, S.-H.
AU - Hardwick, L. J.
AU - Freunberger, Stefan Alexander
AU - Bruce, P. G.
AU - Thackeray, M. M.
ID - 7317
IS - 5
JF - Electrochemical and Solid-State Letters
SN - 1099-0062
TI - Activated Lithium-Metal-Oxides as catalytic electrodes for Li–O2 cells
VL - 14
ER -
TY - JOUR
AB - The nonaqueous rechargeable lithium–O2 battery containing an alkyl carbonate electrolyte discharges by formation of C3H6(OCO2Li)2, Li2CO3, HCO2Li, CH3CO2Li, CO2, and H2O at the cathode, due to electrolyte decomposition. Charging involves oxidation of C3H6(OCO2Li)2, Li2CO3, HCO2Li, CH3CO2Li accompanied by CO2 and H2O evolution. Mechanisms are proposed for the reactions on discharge and charge. The different pathways for discharge and charge are consistent with the widely observed voltage gap in Li–O2 cells. Oxidation of C3H6(OCO2Li)2 involves terminal carbonate groups leaving behind the OC3H6O moiety that reacts to form a thick gel on the Li anode. Li2CO3, HCO2Li, CH3CO2Li, and C3H6(OCO2Li)2 accumulate in the cathode on cycling correlating with capacity fading and cell failure. The latter is compounded by continuous consumption of the electrolyte on each discharge.
AU - Freunberger, Stefan Alexander
AU - Chen, Yuhui
AU - Peng, Zhangquan
AU - Griffin, John M.
AU - Hardwick, Laurence J.
AU - Bardé, Fanny
AU - Novák, Petr
AU - Bruce, Peter G.
ID - 7316
IS - 20
JF - Journal of the American Chemical Society
SN - 0002-7863
TI - Reactions in the rechargeable Lithium–O2 battery with alkyl carbonate electrolytes
VL - 133
ER -
TY - JOUR
AB - Spectroscopic data (see picture) provide direct evidence that in non‐aqueous Li+ electrolyte, O2 is reduced to O2−, which then forms LiO2 on the electrode surface which disproportionates to Li2O2. On charging, Li2O2 decomposes directly, in a one‐step reaction to evolve O2 and does not pass through LiO2 as an intermediate.
AU - Peng, Zhangquan
AU - Freunberger, Stefan Alexander
AU - Hardwick, Laurence J.
AU - Chen, Yuhui
AU - Giordani, Vincent
AU - Bardé, Fanny
AU - Novák, Petr
AU - Graham, Duncan
AU - Tarascon, Jean-Marie
AU - Bruce, Peter G.
ID - 7315
IS - 28
JF - Angewandte Chemie International Edition
SN - 1433-7851
TI - Oxygen reactions in a non-aqueous Li+ electrolyte
VL - 50
ER -
TY - JOUR
AB - The decomposition reaction of H2O2 aqueous solutions (H2O2 - H2O + 1/2O2) catalyzed by transition metal oxide powders has been compared with the charging voltage of nonaqueous Li-O2 cells containing the same catalyst. An inverse linear relationship between Ln k (rate constant for the H2O2 decomposition) and the charging voltage has been found, despite differences in media and possible mechanistic differences. The results suggest that the decomposition may be a reliable, useful, and fast screening tool for materials that promote the charging process of the Li-O2 battery and may ultimately give insight into the charging mechanism.
AU - Giordani, V.
AU - Freunberger, Stefan Alexander
AU - Bruce, P. G.
AU - Tarascon, J.-M.
AU - Larcher, D.
ID - 7318
IS - 12
JF - Electrochemical and Solid-State Letters
SN - 1099-0062
TI - H2O2 decomposition reaction as selecting tool for catalysts in Li–O2 cells
VL - 13
ER -
TY - JOUR
AB - In the first paper of this series, an experimental technique for measuring the current-density distribution with a resolution better than the sub-millimeter scale of the channel and rib structures in the flow-field plates of polymer electrolyte fuel cells (PEFCs) was introduced. This method is extended to the determination of local membrane resistance with the same spatial resolution in the present paper. The combined measurement of current and resistance allows for investigating the interaction of mass- and charge-transport processes, which determine the local rate distribution across the domain of channels and ribs. Therewith, the influence of relevant operating parameters such as reactant composition, dew points, and cell compression on local current generation is investigated. The results show that the distribution of water and oxidant across the channel and rib are the main reasons for significant current gradients on a scale smaller than a millimeter. Humidity variation mainly affects the membrane resistance under the channel, while reactant concentration predominantly influences current generation under the rib-covered cell area.
AU - Reum, Mathias
AU - Freunberger, Stefan Alexander
AU - Wokaun, Alexander
AU - Büchi, Felix N.
ID - 7319
IS - 3
JF - Journal of The Electrochemical Society
SN - 0013-4651
TI - Measuring the current distribution with sub-millimeter resolution in PEFCs: II. Impact of operating parameters
VL - 156
ER -
TY - JOUR
AB - Cell interaction phenomena in polymer electrolyte fuel cell stacks that arise from imbalance between adjacent cells are investigated in detail experimentally and theoretically. A specialized two-cell stack with advanced localized diagnostics was developed and used to analyze the mechanism and effect of cell-to-cell coupling as a result of operationally relevant variations in reactant feed flow. Contributions to overall and local voltage changes with respect to uniformly operated cells are scrutinized. Unequal operation of the cells causes in-plane current in the bipolar plate to redistribute current and result in inhomogeneous polarization. Both increasing and decreasing polarization along the air-flow path reduces cell power as compared to isopotential operation. A two-dimensional model based on a commercial computational fluid dynamics code is used to back and extend the experimental results to more general cases. Furthermore, the experimental setup presented allowed for the first time to perform simultaneous localized electrochemical impedance spectroscopy beyond the single-cell level. The mechanism of mutual cell interaction on local and integral spectra is revealed. Results show that virtually identical operation of the cells is essential to obtain meaningful integral spectra.
AU - Freunberger, Stefan Alexander
AU - Schneider, Ingo A.
AU - Sui, Pang-Chieh
AU - Wokaun, Alexander
AU - Djilali, Nedjib
AU - Büchi, Felix N.
ID - 7321
IS - 7
JF - Journal of The Electrochemical Society
SN - 0013-4651
TI - Cell interaction phenomena in polymer electrolyte fuel cell stacks
VL - 155
ER -
TY - JOUR
AB - A comparative, experimental diffusivity study of gas diffusion layer (GDL) materials for polymer electrolyte fuel cells (PEFC) is presented for the first time. The GDL plays an important role for electrochemical losses due to gas transport limitations at high current densities. Characterization and optimization of these layers is therefore essential to improve power density. A recently developed method which allows for fast diffusimetry is applied and data compared to the literature values. Measurements are made as a function of direction and compression and the effect of different binder structures and hydrophobic treatments on effective diffusivities are discussed. A better understanding of the results is gained by including novel GDL cross-section images and a meaningful unit cell model for the interpretation of the data. The diffusivity data is valuable for GDL manufacturers and future PEFC models. The study reveals that a binder–fiber ratio larger than 50% has a negative impact on the effective diffusion properties. The hydrophobic treatment which is necessary to improve the water management can impede diffusion and thus reduce the power density. Furthermore binder has an isotropic effect while compression pronounces the in-plane orientation of the fibers.
AU - Flückiger, Reto
AU - Freunberger, Stefan Alexander
AU - Kramer, Denis
AU - Wokaun, Alexander
AU - Scherer, Günther G.
AU - Büchi, Felix N.
ID - 7320
IS - 2
JF - Electrochimica Acta
SN - 0013-4686
TI - Anisotropic, effective diffusivity of porous gas diffusion layer materials for PEFC
VL - 54
ER -
TY - JOUR
AB - The gas diffusion layers (GDLs) of a membrane electrode assembly (MEA) serve as link between flow field and porous electrode within a polymer electrolyte fuel cell. Beside ensuring sufficient electrical and thermal contact between the whole electrode area and the flow field, these typically 200–400 μm thick porous structures enable the access of educts to the electrode area which would be occluded by the flow field lands if the flow field is directly attached to the electrode. Hence, the characterisation of properties pertaining to mass transport of educts and products through these structures is indispensable whilst examining the contribution of the GDLs to the overall electrochemical characteristics of a MEA. A fast and cost effective method to measure the effective diffusivity of a GDL is presented. Electrochemical impedance spectroscopy is applied to measure the effective ionic conductivity of an electrolyte-soaked GDL. Taking advantage of the analogy between Ficks and Ohms law, this provides a measure for the effective diffusivity. The method is described in detail, including experimental as well as theoretical aspects, and selected results, highlighting the anisotropy and dependence on the degree of compression, are shown. Moreover, a two-dimensional model consisting of regularly spaced ellipses is developed to represent the porous structure of the GDL, and by using conformal maps, the agreement between this model and experiment with respect to the sensitivity of the effective diffusivity towards compression is shown.
AU - Kramer, Denis
AU - Freunberger, Stefan Alexander
AU - Flückiger, Reto
AU - Schneider, Ingo A.
AU - Wokaun, Alexander
AU - Büchi, Felix N.
AU - Scherer, Günther G.
ID - 7322
IS - 1
JF - Journal of Electroanalytical Chemistry
SN - 1572-6657
TI - Electrochemical diffusimetry of fuel cell gas diffusion layers
VL - 612
ER -
TY - CONF
AB - The propagation of single cell performance losses to adjacent cells in a polymer electrolyte fuel cell stack is studied by means of local current density measurements in a two cell stack. In this stack, the working conditions of adjacent cells can be controlled independently in order to deliberately change the performance of one cell (inducing cell) and study the coupling effects to the adjacent cell (response cell), while keeping the working conditions of the later one unchanged. The experiments have shown that changes in the current density distribution caused by lowering of the air stoichiometry in the inducing cell cause changes in the current density distribution of the response cell in the order of 60% of the change of the inducing cell, even when the air stoichiometry of the response cell is kept constant. The losses in cell voltage of the inducing cell cause losses in cell voltage of the response cell in a magnitude between 30 and 50%.
AU - Santis, Marco
AU - Freunberger, Stefan Alexander
AU - Papra, Matthias
AU - Büchi, Felix N.
ID - 7425
SN - 0791837645
T2 - 3rd International Conference on Fuel Cell Science, Engineering and Technology
TI - Experimental investigation of the propagation of local current density variations to adjacent cells in PEFC stacks
ER -
TY - JOUR
AB - Our experimental results shown here disprove that finite diffusion can generally be assumed in ac impedance models for H2/air-polymer electrolyte fuel cells (PEFCs) to account for the diffusive transport of oxygen through the gas diffusion layer (GDL) toward the air electrode. It is shown that the amplitude of the oxygen concentration oscillation created as a consequence of superimposed ac current at the air electrode is not zero at the channel/GDL interface but extends into the gas channels, at least below modulation frequencies of fmod=10 Hz . By this, sinusoidal oxygen-concentration oscillations within the cathode gas channels are excited locally along the flow field. Due to the forced air convection in the cathode flow-field channels, a coupling via the gas phase occurs downstream of the flow field. The coupling strongly affects the local and by this the overall impedance response of the cell and evokes the formation of a low-frequency arc in H2/air-PEFC impedance spectra. Based on the experimental results, a qualitative model is presented explaining the local impedance response of a segmented 200cm2H2/air PEFC.
AU - Schneider, I. A.
AU - Freunberger, Stefan Alexander
AU - Kramer, D.
AU - Wokaun, A.
AU - Scherer, G. G.
ID - 7325
IS - 4
JF - Journal of The Electrochemical Society
SN - 0013-4651
TI - Oscillations in gas channels: Part I. The forgotten player in impedance spectroscopy in PEFCs
VL - 154
ER -
TY - JOUR
AB - The main factors for reducing the consumption of a vehicle are reduction of curb weight, air drag and increase in the drivetrain efficiency. Highly efficient drivetrains can be developed based on PEFC technology and curb weight may be limited by an innovative vehicle construction. In this paper, data on consumption and efficiency of a four‐place passenger vehicle with a curb weight of 850 kg and an H2/O2 fed PEFC/Supercap hybrid electric powertrain are presented. Hydrogen consumption in the New European Driving Cycle is 0.67 kg H2/100 km, which corresponds to a gasoline equivalent consumption of 2.5 l/100 km. When including the energy needed to supply pure oxygen, the calculated consumption increases from 0.67 to 0.69–0.79 kg H2/100 km, depending on the method of oxygen production.
AU - Büchi, F. N.
AU - Paganelli, G.
AU - Dietrich, P.
AU - Laurent, D.
AU - Tsukada, A.
AU - Varenne, P.
AU - Delfino, A.
AU - Kötz, R.
AU - Freunberger, Stefan Alexander
AU - Magne, P.-A.
AU - Walser, D.
AU - Olsommer, D.
ID - 7323
IS - 4
JF - Fuel Cells
SN - 1615-6846
TI - Consumption and efficiency of a passenger car with a Hydrogen/Oxygen PEFC based hybrid electric drivetrain
VL - 7
ER -
TY - JOUR
AB - Efficiency is the key parameter for the application of fuel cells in automotive applications. The efficiency of a hydrogen/oxygen polymer electrolyte fuel cell system is analyzed and compared to hydrogen/air systems. The analysis is performed for the tank to electric power chain. Furthermore, the additional energy required for using pure oxygen as a second fuel is analyzed and included in the calculation. The results show that if hydrogen is produced from primary fossil energy carriers, such as natural gas and pure oxygen needs to be obtained by a conventional process; the fuel to electric current efficiency is comparable for hydrogen/oxygen and hydrogen/air systems. However, if hydrogen and oxygen are produced by the splitting of water, i.e., by electrolysis or by a thermochemical process, the fuel to electric current efficiency for the hydrogen/oxygen system is clearly superior.
AU - Büchi, F. N.
AU - Freunberger, Stefan Alexander
AU - Reum, M.
AU - Paganelli, G.
AU - Tsukada, A.
AU - Dietrich, P.
AU - Delfino, A.
ID - 7324
IS - 2
JF - Fuel Cells
SN - 1615-6846
TI - On the efficiency of an advanced automotive fuel cell system
VL - 7
ER -
TY - JOUR
AB - An experimental technique for measuring the current density distribution with a resolution smaller than the channel/rib scale of the flow field in polymer electrolyte fuel cells (PEFCs) is presented. The electron conductors in a plane perpendicular to the channel direction are considered as two-dimensional resistors. Hence, the current density is obtained from the solution of Laplace's equation with the potentials at current collector and reaction layer as boundary conditions. Using ohmic drop for calculating the local current, detailed knowledge of all resistances involved is of prime importance. In particular, the contact resistance between the gas diffusion layer (GDL) and flow field rib, as well as GDL bulk conductivity, are strongly dependent on clamping pressure. They represent a substantial amount of the total ohmic drop and therefore require careful consideration. The detailed experimental setup as well as the concise procedure for quantitative data evaluation is described. Finally, the method is applied successfully to a cell operated on pure oxygen and air up to high current densities. The results show that electrical and ionic resistances seem to govern the current distribution at low current regimes, whereas mass transport limitations locally hamper the current production at high loads.
AU - Freunberger, Stefan Alexander
AU - Reum, Mathias
AU - Evertz, Jörg
AU - Wokaun, Alexander
AU - Büchi, Felix N.
ID - 7328
IS - 11
JF - Journal of The Electrochemical Society
SN - 0013-4651
TI - Measuring the current distribution in PEFCs with sub-millimeter resolution
VL - 153
ER -
TY - JOUR
AB - Propagation of performance changes to adjacent cells in polymer electrolyte fuel cell stacks is studied by means of voltage monitoring and local current density measurements in peripheral cells of the stack. A technical fuel cell stack has been modified by implementing two independent reactant and coolant supplies in order to deliberately change the performance of one cell (anomalous cell) and study the coupling phenomena to adjacent cells (coupling cells), while keeping the working conditions of the later cell-group unaltered.
Two anomalies are studied: (i) air starvation and (ii) thermal anomaly, in a single anomalous cell in the stack and their coupling to adjacent cells. The results have shown that anomalies inducing considerable changes in the local current density of the anomalous cell (such as air starvation) propagate to adjacent cells affecting their performance. The propagation of local current density changes takes place via the common bipolar plate due to its finite thickness and in-plane conductivity. Consequently, anomalies which do not strongly influence the local current density distribution (such as a thermal anomaly under the studied working conditions) do not propagate to adjacent cells.
AU - Santis, Marco
AU - Freunberger, Stefan Alexander
AU - Papra, Matthias
AU - Wokaun, Alexander
AU - Büchi, Felix N.
ID - 7327
IS - 2
JF - Journal of Power Sources
SN - 0378-7753
TI - Experimental investigation of coupling phenomena in polymer electrolyte fuel cell stacks
VL - 161
ER -
TY - CONF
AB - Often the properties of a single cell are considered as representative for a complete polymer electrolyte fuel cell stack or even a fuel cell system. In some cases this comes close, however, in many real cases differences on several scales become important. Cell interaction phenomena in fuel cell stacks that arise from inequalities between adjacent cells are investigated in detail experimentally. For that, a specialized 2-cell stack with advanced localized diagnostics was developed. The results show that inequalities propagate by electrical coupling, inhomogeneous cell polarization and inducing in-plane current in the common bipolar plate. The effects of the different loss-mechanisms are analyzed and quantified.
AU - Büchi, Felix N.
AU - Freunberger, Stefan Alexander
AU - Santis, Marco
ID - 7326
IS - 1
T2 - ECS Transactions
TI - What is learned beyond the scale of single cells?
VL - 3
ER -
TY - JOUR
AB - A novel measurement principle for measuring the current distribution in polymer electrolyte fuel cells (PEFCs) is introduced. It allows, in contrast to all other known techniques, for the first time for a resolution smaller than the channel/rib scale of the flow field in PEFCs. The current density is obtained by considering the electron conductors in the cell as a two-dimensional resistor with the voltage drop caused by the current. The method was applied to a cell operated on oxygen up to high current densities. The results show that the ohmic resistances govern the current distribution in the low current regime, whereas mass transport limitations hamper the current production under the land at high loads.
AU - Freunberger, Stefan Alexander
AU - Reum, Mathias
AU - Wokaun, Alexander
AU - Büchi, Felix N.
ID - 7329
IS - 9
JF - Electrochemistry Communications
SN - 1388-2481
TI - Expanding current distribution measurement in PEFCs to sub-millimeter resolution
VL - 8
ER -
TY - JOUR
AB - Polymer electrolyte fuel cells (PE fuel cells) working with air at low stoichiometries (<2.0) and standard electrochemical components show a high degree of inhomogeneity in the current density distribution over the active area. An inhomogeneous current density distribution leads to a non-uniform utilization of the active area, which could negatively affect the time of life of the cells. Furthermore, it is also believed to lower cell performance. In this work, the homogenization of the current density, realized by means of tailored cathodes with along-the-air-channel redistributed catalyst loadings, is investigated. The air stoichiometry range for which a homogenization of the current density is achieved depends upon the gradient with which the catalyst is redistributed along the air channel. A gentle increasing catalyst loading profile homogenizes the current density at relatively higher air stoichiometries, while a steeper profile is suited better for lower air stoichiometries. The results show that a homogenization of the current density by means of redistributed catalyst loading has negative effects on cell performance. Model calculations corroborate the experimental findings on homogenization of the current density and deliver an explanation for the decrease in cell performance.
AU - Santis, M.
AU - Freunberger, Stefan Alexander
AU - Reiner, A.
AU - Büchi, F.N.
ID - 7330
IS - 25
JF - Electrochimica Acta
SN - 0013-4686
TI - Homogenization of the current density in polymer electrolyte fuel cells by in-plane cathode catalyst gradients
VL - 51
ER -
TY - JOUR
AB - A quasi-two-dimensional, along-the-channel mass and heat-transfer model for a proton exchange membrane fuel cell (PEFC) is described and validated against experimental current distribution data. The model is formulated in a dimensional manner, i.e., local transport phenomena are treated one-dimensional in through-plane direction and coupled in-plane by convective transport in the gas and coolant channels. Thus, a two-dimensional slice running through the repetitive unit of a cell from the anode channel via membrane-electrode assembly (MEA) and cathode channel to the coolant channel and from inlet to outlet is modeled. The aim of the work is to elucidate the influence of operating conditions such as feed gas humidities and stoichiometric ratios on the along-the-channel current density distribution and to identify the distinct underlying voltage loss mechanisms. Furthermore, a complicated technical flow field is modeled by a combination of co- and counterflow subdomains and compared with experimental current densities.
AU - Freunberger, Stefan Alexander
AU - Santis, Marco
AU - Schneider, Ingo A.
AU - Wokaun, Alexander
AU - Büchi, Felix N.
ID - 7332
IS - 2
JF - Journal of The Electrochemical Society
SN - 0013-4651
TI - In-plane effects in large-scale PEMFCs
VL - 153
ER -
TY - JOUR
AB - A previously developed mathematical model for water management and current density distribution in a polymer electrolyte fuel cell (PEFCs) is employed to investigate the effects of cooling strategies on cell performance. The model describes a two-dimensional slice through the cell along the channels and through the entire cell sandwich including the coolant channels and the bipolar plate. Arbitrary flow arrangements of fuel, oxidant, and coolant stream directions can be described. Due to the serious impact of temperature on all processes in the PEFC, both the relative direction of the coolant stream to the gas streams and its mass flow turns out to significantly affect the cell performance. Besides influencing the electrochemical reaction and all kinds of mass transfer temperature, variations predominantly alter the local membrane hydration distribution and subseqently its conductivity.
AU - Freunberger, Stefan Alexander
AU - Wokaun, Alexander
AU - Büchi, Felix N.
ID - 7331
IS - 5
JF - Journal of The Electrochemical Society
SN - 0013-4651
TI - In-plane effects in large-scale PEFCs: II. The influence of cooling strategy on cell performance
VL - 153
ER -
TY - JOUR
AB - Fundamental and phenomenological models for cells, stacks, and complete systems of PEFC and SOFC are reviewed and their predictive power is assessed by comparing model simulations against experiments. Computationally efficient models suited for engineering design include the (1+1) dimensionality approach, which decouples the membrane in-plane and through-plane processes, and the volume-averaged-method (VAM) that considers only the lumped effect of pre-selected system components. The former model was shown to capture the measured lateral current density inhomogeneities in a PEFC and the latter was used for the optimization of commercial SOFC systems. State Space Modeling (SSM) was used to identify the main reaction pathways in SOFC and, in conjunction with the implementation of geometrically well-defined electrodes, has opened a new direction for the understanding of electrochemical reactions. Furthermore, SSM has advanced the understanding of the COpoisoning-induced anode impedance in PEFC. Detailed numerical models such as the Lattice Boltzmann (LB) method for transport in porous media and the full 3-D Computational Fluid Dynamics (CFD) Navier-Stokes simulations are addressed. These models contain all components of the relevant physics and they can improve the understanding of the related phenomena, a necessary condition for the development of both appropriate simplified models as well as reliable technologies. Within the LB framework, a technique for the characterization and computer-reconstruction of the porous electrode structure was developed using advanced pattern recognition algorithms. In CFD modeling, 3-D simulations were used to investigate SOFC with internal methane steam reforming and have exemplified the significance of porous and novel fractal channel distributors for the fuel and oxidant delivery, as well as for the cooling of PEFC. As importantly, the novel concept has been put forth of functionally designed, fractal-shaped fuel cells, showing promise of significant performance improvements over the conventional rectangular shaped units. Thermo-economic modeling for the optimization of PEFC is finally addressed.
AU - Mantzaras, John
AU - Freunberger, Stefan Alexander
AU - Büchi, Felix N.
AU - Roos, Markus
AU - Brandstätter, Wilhelm
AU - Prestat, Michel
AU - Gauckler, Ludwig J.
AU - Andreaus, Bernhard
AU - Hajbolouri, Faegheh
AU - Senn, Stephan M.
AU - Poulikakos, Dimos
AU - Chaniotis, Andreas K.
AU - Larrain, Diego
AU - Autissier, Nordahl
AU - Maréchal, François
ID - 7334
IS - 12
JF - CHIMIA International Journal for Chemistry
SN - 0009-4293
TI - Fuel cell modeling and simulations
VL - 58
ER -
TY - JOUR
AB - The analysis of the complete H2/air polymer electrolyte fuel cell system shows that process air humidification is one of the biggest obstacles for a high performance portable system in the kW range. Therefore, a new concept, with passive process air humidification integrated into the stack, has been developed. Humidification in each cell makes the process independent from the number of cells and the operation mode, thus making the concept fully scalable. Without external humidification the system is simpler, smaller, and cheaper. The humidification of the process air is achieved by transfer of product water from the exhaust air, through part of the membrane, to the dry intake air. Tests have shown that cells using the concept of internal humidification and operated with dry air at 70 ° have almost the same performance as when operated with external humidification. A 42‐cell stack with this internal humidification concept was built and integrated into a portable 1 kW power generator system.
AU - Santis, M.
AU - Schmid, D.
AU - Ruge, M.
AU - Freunberger, Stefan Alexander
AU - Büchi, F.N.
ID - 7333
IS - 3
JF - Fuel Cells
SN - 1615-6846
TI - Modular stack-internal air humidification concept-verification in a 1 kW stack
VL - 4
ER -