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One of the key factors responsible for the poor cycleability of Li–O2 batteries is a formation of byproducts from irreversible reactions between electrolyte and discharge product Li2O2 and/or intermediate LiO2. Among many solvents that are used as electrolyte component for Li–O2 batteries, acetonitrile (MeCN) is believed to be relatively stable towards oxidation. Using near ambient pressure X-ray photoemission spectroscopy (NAP XPS), we characterized the reactivity of MeCN in the Li–O2 battery. For this purpose, we designed the model electrochemical cell assembled with solid electrolyte. We discharged it first in O2 and then exposed to MeCN vapor. Further, the discharge was carried out in O2 + MeCN mixture. We have demonstrated that being in contact with Li–O2 discharge products, MeCN oxidizes. This yields species that are weakly bonded to the surface and can be easily desorbed. That’s why they cannot be detected by the conventional XPS. Our results suggest that the respective chemical process most probably does not give rise to electrode passivation but can decrease considerably the Coulombic efficiency of the battery., This work of A.K-G., J.J.V-V. and D.M.I. was supported by the Russian Ministry of Science and Education (RFMEFI61614×0007) and Bundesministerium für Bildung and Forschung (Project No. 05K2014) in the framework of the joint Russian-German research project “SYnchrotron and NEutron STudies for Energy Storage (SYNESTESia)”. T.K.Z acknowledges Center for Electrochemical Energy of Skolkovo Institute of Science and Technology for financial support. The work of O.O.K., A.I.B and L.V.Y. is performed within the joint project of the Russian Science Foundation (16-42-01093) and DFG (LA655-17/1). We are grateful to HZB for beamtime granted at ISISS and RGBL beamlines. T.K.Z. and A.S.F. thank to the Russian German laboratory at HZB for support provided. Authors are appreciated to Victor Vizgalov for solid electrolyte membrane preparation. Travelling of T.K.Z. was supported by German-Russian Interdisciplinary Science Center (G-RISC).

The behavior of ternary mixed crystals or solid solutions and its correlation with the properties of their binary constituents is of fundamental interest. Due to their unique potential for application in future information technology, mixed crystals of topological insulators with the spin-locked, gapless states on their surfaces attract huge attention of physicists, chemists and material scientists. (Bi1−xSbx)2Te3 solid solutions are among the best candidates for spintronic applications since the bulk carrier concentration can be tuned by varying x to obtain truly bulk-insulating samples, where the topological surface states largely contribute to the transport and the realization of the surface quantum Hall effect. As this ternary compound will be evidently used in the form of thin-film devices its chemical stability is an important practical issue. Based on the atomic resolution HAADF-TEM and EDX data together with the XPS results obtained both ex situ and in situ, we propose an atomistic picture of the mixed crystal reactivity compared to that of its binary constituents. We find that the surface reactivity is determined by the probability of oxygen attack on the Te–Sb bonds, which is directly proportional to the number of Te atoms bonded to at least one Sb atom. The oxidation mechanism includes formation of an amorphous antimony oxide at the very surface due to Sb diffusion from the first two quintuple layers, electron tunneling from the Fermi level of the crystal to oxygen, oxygen ion diffusion to the crystal, and finally, slow Te oxidation to the +4 oxidation state. The oxide layer thickness is limited by the electron transport, and the overall process resembles the Cabrera–Mott mechanism in metals. These observations are critical not only for current understanding of the chemical reactivity of complex crystals, but also to improve the performance of future spintronic devices based on topological materials.

Unfortunately, the practical applications of Li-O2 batteries are impeded by poor rechargeability. Here, for the first time we show that superoxide radicals generated at the cathode during discharge react with carbon that contains activated double bonds or aromatics to form epoxy groups and carbonates, which limits the rechargeability of Li-O2 cells. Carbon materials with a low amount of functional groups and defects demonstrate better stability thus keeping the carbon will-o'-the-wisp lit for lithium-air batteries.

One of the key problems hindering practical implementation of lithium–air batteries is caused by carbon cathode chemical instability leading to low energy efficiency and short cycle life. Titanium carbide (TiC) nanopowders are considered as an alternative cathode material; however, they are intrinsically reactive toward oxygen, and its stability is controlled totally by a surface overlayers. Using photoemission spectroscopy, we show that lithium–air battery discharge product, lithium peroxide (Li2O2), easily oxidizes clean TiC surface. At the same time, TiC surface, which was treated by molecular oxygen under ambient conditions, shows much better stability in contact with Li2O2 that can be explained by the presence of a surface layer containing a significant amount of elemental carbon in addition to oxides and oxycarbides. Nevertheless, such protective coatings produced by room temperature oxidation are not practically useful as one of its components, elemental carbon, is oxidized in the presence of lithium–air battery discharge intermediates. These results are of critical importance in understanding of TiC surface chemistry and in design of stable lithium–air battery electrodes. We postulate that dense, uniform, carbon-free titanium dioxide surface layers of 2–3 nm thickness on TiC will be a promising solution, and thus further efforts should be taken for developing synthetic protocols enabling preparation of TiO2/TiC core–shell structures., This work was financially supported by the Russian Ministry of Science and Education (RFMEFI61614X0007) and Bundesministerium für Bildung and Forschung (project no. 05K2014) in the framework of the joint Russian-German research project “SYnchrotron and NEutron STudies for Energy Storage (SYNESTESia)”.

A new protected anode for lithium-air batteries is designed using lithium foil and lithium–aluminium–germanium–phosphorus glass–ceramics (LAGP) with improved specific conductivity exceeding 3.1 ⋅ 10− 4 S cm− 1 at 80 °C and 1.4 ⋅ 10− 4 S cm− 1 at − 20 °C. Prevention of anode or electrolyte degradation provided stability of the battery characteristics for at least 10 cycles. In particular, a lithium-air battery with the protected anode and an activated carbon cathode modified with α-MnO2 nanorod catalyst showed a specific capacity of about 3000 mAh g− 1.