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

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 O Se as anodes for lithium-ion batteries (LIBs) and potassium-ion batteries (PIBs). Surprisingly, the Bi O Se/graphite composite electrode shows even better cycle stability for PIBs. The electrochemical reaction mechanisms of the Bi O 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 -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 anions in Bi O Se, where multiple Li–Se intermediates rather than the traditional single-phase Li 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. 2 2 2 2 2 2 III 2 2 2 2−