(Invited) Anionic Redox Chemistry in Layered Oxide Cathodes

Abstract

Li-ion battery remains as the critical energy storage device and starts to invade the large electrical vehicle (EV) market. Extensive efforts have been devoted to developing advanced layered oxide cathodes, including both stoichiometric and Li-rich layered oxides, for Li-ion batteries of even better performance. For all these cathodes, there is a clear need for the high-voltage cycling to obtain an even higher practical capacity. However, the redox reactions become more complex when charged at high voltages. Beyond the conventional transition metal (TM) redox, anionic oxygen becomes active and participates in the electrochemical reaction in these cathodes. The anionic oxygen activity involves both the reversible oxygen redox and irreversible oxygen loss accompanied by other byproducts resulting from the undesirable side reactions at high voltages.In the past, my group has been focusing on understanding the redox chemistry, including both cationic and anionic redox reactions, in both stoichiometric and Li-rich layered oxide cathodes, especially towards the high-voltage cycling. We specifically investigated the electronic states of TM and O using combined electrochemical, soft X-ray absorption (XAS), resonant inelastic X-ray spectroscopy (RIXS) and in situ differential electrochemical mass spectrometry (DEMS) in the high voltage region to elucidate the explicit redox chemistry in various layered oxide cathodes. This presentation will highlight a summary on the different TM and O redox behaviors in these technologically relevant cathode materials for a close comparison. Of particular interest is the fundamental understanding of how the anionic oxygen participates in the electrochemistry of layered oxides with the presence of different Li and TM stoichiometry.