Chemo-mechanical limitations of liquid alloy anodes for sodium solid-state batteries

Abstract

Sodium–potassium (NaK) liquid metal anodes address interfacial challenges in sodium solid-state batteries by eliminating solid–solid contact issues of solid Na anodes. Operando galvanostatic electrochemical impedance spectroscopy and in situ synchrotron X-ray computed tomography experiments reveals that interfacial Na depletion upon electrodissolution results in void formation and K metal precipitation. Conversely, Na plating upon electrodeposition results in local Na accumulation at the interface. Long-term deposition results in Na filament growth and short-circuit failure. These degradation processes arise from poor wetting due to the high surface tension of NaK and its limited Na diffusivity. Strategies which reduce the tendency for segregation are necessary for long-term cycling.