Evolution\nof Interfacial Electro-Chemo-Mechanics between\nLithium Metal and Halide Solid Electrolyte

The\nelectro-chemo-mechanic phenomena that play a crucial\nrole in\nthe stability of halide solid electrolytes with Li metal at the interface\nare unknown. Moreover, in a halide SE, the central M atom is known\nto dictate its reactivity with Li metal. To understand this chemical\ncomposition-dependent reactivity of halide SE, we have taken three\nhalide solid electrolytes, namely Li<sub>3</sub>InCl<sub>6</sub>,\nLi<sub>2</sub>ZrCl<sub>6</sub>, and Li<sub>3</sub>YCl<sub>6</sub>.\nHere, we use operando X-ray photoelectron spectroscopy during Li plating\nto understand the reaction kinetics leading to the interphase evolution\nand interphase composition. The interphase evolution in symmetric\ncells was further monitored by operando electrochemical impedance\nspectroscopy and operando pressure measurements, showing the complex\nintertwining of molar volume change, void formation, and interphase\ngrowth. The as-grown interphase was visualized by focused ion beam\nscanning electron microscopy. The chemical reactivity was confirmed\nby bond strength calculations using operando synchrotron X-ray diffraction.\nWe confirm volume changes due to molar volume mismatch leading to\ndifferent microstructures of interphases for the three-halide solid\nelectrolytes, which are correlated to the impedance growth during\nelectrochemistry by operando impedance measurements, showing molar\nvolume change has a drastic effect on the reactivity.