Synchrotron X‐Ray Absorption Spectroscopy and Electrochemical Study of Bi2O2Se Electrode for Lithium‐/Potassium‐Ion Storage

Abstract Elucidating the battery operating mechanism is important for designing better conversion‐type anodes as it determines the strategies used to improve electrochemical performances. Herein, the authors pioneered the electrochemical study of layered Bi 2 O 2 Se as anodes for lithium‐ion batteries (LIBs) and potassium‐ion batteries (PIBs). Surprisingly, the Bi 2 O 2 Se/graphite composite electrode shows even better cycle stability for PIBs. The electrochemical reaction mechanisms of the Bi 2 O 2 Se/graphite electrode for LIBs and PIBs are investigated by potential‐resolved in situ and ex situ X‐ray absorption spectroscopy based at the Bi L III ‐edge and Se K‐edge through characterizing the local atomic structure evolution, valence state change, and charge transfer. New insights are gained regarding the electrochemical process of Se 2− anions in Bi 2 O 2 Se, where multiple Li–Se intermediates rather than the traditional single‐phase Li 2 Se are involved in this conversion‐type anode. The advanced understanding of anionic electrochemistry in conversion‐type anodes prompts one to find appropriate ways to suppress side‐reactions and improve the battery performances.