@article{9447, abstract = {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.}, author = {Maffre, Marion and Bouchal, Roza and Freunberger, Stefan Alexander and Lindahl, Niklas and Johansson, Patrik and Favier, Frédéric and Fontaine, Olivier and Bélanger, Daniel}, issn = {1945-7111}, journal = {Journal of The Electrochemical Society}, keywords = {Renewable Energy, Sustainability and the Environment, Electrochemistry, Materials Chemistry, Electronic, Optical and Magnetic Materials, Surfaces, Coatings and Films, Condensed Matter Physics}, number = {5}, publisher = {IOP Publishing}, title = {{Investigation of electrochemical and chemical processes occurring at positive potentials in “Water-in-Salt” electrolytes}}, doi = {10.1149/1945-7111/ac0300}, volume = {168}, year = {2021}, } @unpublished{9978, abstract = {Redox mediators could catalyse otherwise slow and energy-inefficient cycling of Li-S and Li-O 2 batteries by shuttling electrons/holes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.}, author = {Cao, Deqing and Shen, Xiaoxiao and Wang, Aiping and Yu, Fengjiao and Wu, Yuping and Shi, Siqi and Freunberger, Stefan Alexander and Chen, Yuhui}, booktitle = {Research Square}, issn = {2693-5015}, keywords = {Catalysis, Energy engineering, Materials theory and modeling}, pages = {21}, publisher = {Research Square}, title = {{Sharp kinetic acceleration potentials during mediated redox catalysis of insulators}}, doi = {10.21203/rs.3.rs-750965/v1}, year = {2021}, } @unpublished{9980, abstract = {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.}, author = {Prehal, Christian and Talian, Sara Drvarič and Vizintin, Alen and Amenitsch, Heinz and Dominko, Robert and Freunberger, Stefan Alexander and Wood, Vanessa}, booktitle = {Research Square}, keywords = {Li2S, Lithium Sulphur Batteries, SAXS, WAXS}, pages = {21}, title = {{Mechanism of Li2S formation and dissolution in Lithium-Sulphur batteries}}, doi = {10.21203/rs.3.rs-818607/v1}, year = {2021}, } @article{9250, abstract = {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.}, author = {Petit, Yann K. and Mourad, Eléonore and Prehal, Christian and Leypold, Christian and Windischbacher, Andreas and Mijailovic, Daniel and Slugovc, Christian and Borisov, Sergey M. and Zojer, Egbert and Brutti, Sergio and Fontaine, Olivier and Freunberger, Stefan Alexander}, issn = {1755-4349}, journal = {Nature Chemistry}, keywords = {General Chemistry, General Chemical Engineering}, number = {5}, pages = {465--471}, publisher = {Springer Nature}, title = {{Mechanism of mediated alkali peroxide oxidation and triplet versus singlet oxygen formation}}, doi = {10.1038/s41557-021-00643-z}, volume = {13}, year = {2021}, } @article{7672, abstract = {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.}, author = {Samojlov, Aleksej and Schuster, David and Kahr, Jürgen and Freunberger, Stefan Alexander}, journal = {Electrochimica Acta}, number = {12}, publisher = {Elsevier}, title = {{Surface and catalyst driven singlet oxygen formation in Li-O2 cells}}, doi = {10.1016/j.electacta.2020.137175}, volume = {362}, year = {2020}, } @article{7847, abstract = {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. }, author = {Bouchal, Roza and Li, Zhujie and Bongu, Chandra and Le Vot, Steven and Berthelot, Romain and Rotenberg, Benjamin and Favier, Fréderic and Freunberger, Stefan Alexander and Salanne, Mathieu and Fontaine, Olivier}, issn = {1521-3773}, journal = {Angewandte Chemie International Edition}, number = {37}, pages = {15913--1591}, publisher = {Wiley}, title = {{Competitive salt precipitation/dissolution during free‐water reduction in water‐in‐salt electrolyte}}, doi = {10.1002/anie.202005378}, volume = {59}, year = {2020}, } @article{7985, abstract = {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.}, author = {Kwak, WJ and Sharon, D and Xia, C and Kim, H and Johnson, LR and Bruce, PG and Nazar, LF and Sun, YK and Frimer, AA and Noked, M and Freunberger, Stefan Alexander and Aurbach, D}, issn = {1520-6890}, journal = {Chemical Reviews}, number = {14}, pages = {6626--6683}, publisher = {American Chemical Society}, title = {{Lithium-oxygen batteries and related systems: Potential, status, and future}}, doi = {10.1021/acs.chemrev.9b00609}, volume = {120}, year = {2020}, } @article{8057, abstract = {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.}, author = {Bouchal, Roza and Li, Zhujie and Bongu, Chandra and Le Vot, Steven and Berthelot, Romain and Rotenberg, Benjamin and Favier, Frederic and Freunberger, Stefan Alexander and Salanne, Mathieu and Fontaine, Olivier}, issn = {1521-3757}, journal = {Angewandte Chemie}, number = {37}, pages = {16047--16051}, publisher = {Wiley}, title = {{Competitive salt precipitation/dissolution during free‐water reduction in water‐in‐salt electrolyte}}, doi = {10.1002/ange.202005378}, volume = {132}, year = {2020}, } @misc{8067, abstract = {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.}, author = {Varzi, Alberto and Thanner, Katharina and Scipioni, Roberto and Di Lecce, Daniele and Hassoun, Jusef and Dörfler, Susanne and Altheus, Holger and Kaskel, Stefan and Prehal, Christian and Freunberger, Stefan Alexander}, issn = {2664-1690}, keywords = {Battery, Lithium metal, Lithium-sulphur, Lithium-air, All-solid-state}, pages = {63}, publisher = {IST Austria}, title = {{Current status and future perspectives of Lithium metal batteries}}, doi = {10.15479/AT:ISTA:8067}, year = {2020}, } @unpublished{8081, abstract = {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. }, author = {Hobisch, Mathias A. and Mourad, Eléonore and Fischer, Wolfgang J. and Prehal, Christian and Eyley, Samuel and Childress, Anthony and Zankel, Armin and Mautner, Andreas and Breitenbach, Stefan and Rao, Apparao M. and Thielemans, Wim and Freunberger, Stefan Alexander and Eckhart, Rene and Bauer, Wolfgang and Spirk, Stefan }, title = {{High specific capacitance supercapacitors from hierarchically organized all-cellulose composites}}, year = {2020}, } @article{8329, abstract = {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.}, author = {Schlemmer, Werner and Nothdurft, Philipp and Petzold, Alina and Frühwirt, Philipp and Schmallegger, Max and Gescheidt-Demner, Georg and Fischer, Roland and Freunberger, Stefan Alexander and Kern, Wolfgang and Spirk, Stefan}, issn = {1521-3773}, journal = {Angewandte Chemie International Edition}, number = {51}, pages = {22943--22946}, publisher = {Wiley}, title = {{2‐methoxyhydroquinone from vanillin for aqueous redox‐flow batteries}}, doi = {10.1002/anie.202008253}, volume = {59}, year = {2020}, } @article{8361, abstract = {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.}, author = {Varzi, Alberto and Thanner, Katharina and Scipioni, Roberto and Di Lecce, Daniele and Hassoun, Jusef and Dörfler, Susanne and Altheus, Holger and Kaskel, Stefan and Prehal, Christian and Freunberger, Stefan Alexander}, issn = {0378-7753}, journal = {Journal of Power Sources}, number = {12}, publisher = {Elsevier}, title = {{Current status and future perspectives of lithium metal batteries}}, doi = {10.1016/j.jpowsour.2020.228803}, volume = {480}, year = {2020}, } @article{8568, abstract = {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.}, author = {Prehal, Christian and Fitzek, Harald and Kothleitner, Gerald and Presser, Volker and Gollas, Bernhard and Freunberger, Stefan Alexander and Abbas, Qamar}, issn = {2041-1723}, journal = {Nature Communications}, keywords = {General Biochemistry, Genetics and Molecular Biology, General Physics and Astronomy, General Chemistry}, publisher = {Springer Nature}, title = {{Persistent and reversible solid iodine electrodeposition in nanoporous carbons}}, doi = {10.1038/s41467-020-18610-6}, volume = {11}, year = {2020}, } @misc{9780, abstract = {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°}, author = {Schlemmer, Werner and Nothdurft, Philipp and Petzold, Alina and Riess, Gisbert and Frühwirt, Philipp and Schmallegger, Max and Gescheidt-Demner, Georg and Fischer, Roland and Freunberger, Stefan Alexander and Kern, Wolfgang and Spirk, Stefan}, publisher = {CCDC}, title = {{CCDC 1991959: Experimental Crystal Structure Determination}}, doi = {10.5517/ccdc.csd.cc24vsrk}, year = {2020}, }