Evolution of Interfacial Electro-Chemo-Mechanics between Lithium Metal and Halide Solid Electrolyte

The electro-chemo-mechanic phenomena that play a crucial role in the stability of halide solid electrolytes with Li metal at the interface are unknown. Moreover, in a halide SE, the central M atom is known to dictate its reactivity with Li metal. To understand this chemical composition-dependent reactivity of halide SE, we have taken three halide solid electrolytes, namely Li 3 InCl 6, Li 2 ZrCl 6, and Li 3 YCl 6 . Here, we use operando X-ray photoelectron spectroscopy during Li plating to understand the reaction kinetics leading to the interphase evolution and interphase composition. The interphase evolution in symmetric cells was further monitored by operando electrochemical impedance spectroscopy and operando pressure measurements, showing the complex intertwining of molar volume change, void formation, and interphase growth. The as-grown interphase was visualized by focused ion beam scanning electron microscopy. The chemical reactivity was confirmed by bond strength calculations using operando synchrotron X-ray diffraction. We confirm volume changes due to molar volume mismatch leading to different microstructures of interphases for the three-halide solid electrolytes, which are correlated to the impedance growth during electrochemistry by operando impedance measurements, showing molar volume change has a drastic effect on the reactivity.