Ultra-high areal capacity Li electrodeposition at metal-solid electrolyte interfaces under minimal stack pressures enabled by interfacial Na-K liquids

The need for higher energy density rechargeable batteries has generated interest in metallic electrodes paired with solid electrolytes. However, impedance growth at the Li metal-solid electrolytes interface due to void formation during cycling at practical current densities and areal capacities, e.g., greater than 0.5 mA cm-2 and 1.5 mAh cm-2 respectively, remains a significant barrier. Here, we show that introducing a wetting interfacial film of Na-K liquid between Li metal and Li6.75La3Zr1.75Ta0.25O12 (LLZTO) solid electrolyte permits reversible stripping and plating of up to 150μm of Li (30 mAhcm-2), approximately ten times the areal capacity of today’s lithium-ion batteries, at current densities above 0.5 mA cm-2 and stack pressures below 75 kPa, all with minimal changes in cell impedance. We further show that this increase in the accessible areal capacity at high stripping current densities is due to the presence of Na-K liquid at the Li stripping interface; this performance improvement is not enabled in the absence of the Na-K liquid. This design approach holds promise for overcoming interfacial stability issues that have heretofore limited performance of solid-state metal batteries.