Unveiling complex lithiation/delithiation mechanism in AgNbO3 model perovskite using operando X-ray absorption spectroscopy

In AgNbO 3 perovskite structure, electrochemical activation is speculated during the first lithiation cycle enabling the material to reversibly store Li + by the contributions of both Ag and Nb cation. However, the origin of electrochemically induced structural activation and understanding of cations involvement in complex Li + storage mechanism is still elusive. Herein, operando synchrotron X-ray absorption spectroscopy (XAS) was applied to clarify this mechanism under different cycling conditions. Ag K-edge XAS measurements during first lithiation revealed a gradual Ag + to Ag 0 reduction starting at a relatively high potential of 1.0 V vs Li + /Li, thus creating vacancies in the lattice for Li + insertion and inducing a crystalline-to-amorphous structural transition. Below 0.3 V vs Li, metallic Ag forms multiple intermetallic Li-Ag alloys, resulting in lithium rich Li 9 Ag at the end of lithiation. Simultaneously, Nb K-edge XAS measurements indicate an irreversible Nb 5+ to Nb 3+ reduction with formation of metastable phases. Upon extended cycling at high current densities, intermediate phases sustain reversible Li + storage through synergistic Nb-redox activity and Li-Ag (de)alloying reactions, facilitating fast charging capability. This study will help in designing new conversion-alloying type negative electrodes for fast-charging batteries.