Temperature and Pressure Effects on Unrecoverable Voids in Li Metal Solid-State Batteries

All-solid-state batteries (ASSB) can potentially achieve high gravimetric and volumetric energy densities (900 Wh/L) if paired with a lithium metal anode and solid electrolyte. However, there is a lack in critical understanding about how to operate lithium metal cells at high capacities and minimize unwanted degradation mechanisms such as dendrites and voids. Herein, we investigate how pressure and temperature influence the formation and annihilation of unrecoverable voids in lithium metal upon stripping. Stack pressure and temperature are effective means to initiate creep-induced void filling and decrease charge transfer resistances. Applying stack pressure enables lithium to deform and creep below the yield stress during stripping at high current densities. Lithium creep is not sufficient to prevent cell shorting during plating. Three-electrode experiments were employed to probe the kinetic and morphological limitations that occur at the anode-solid electrolyte during high-capacity stripping (5 mAh/cm²). The role of cathode-LLZO interface, which dictates cyclability and capacity retention in full cells, was also studied. This work elucidates the important role that temperature (external or in situ generated) has on reversible operation of solid-state batteries.