Liquid Electrolyte-Assisted Stabilization of the LLZO/Li Interface for Stable Lithium Metal Batteries

Abstract

Garnet-based solid-state batteries offer high energy density and improved safety but face challenges such as poor interfacial compatibility and high resistance at the LLZO|Li interface due to their lithophobic nature. To address these issues, we applied a small amount of carbonate- and ether-based liquid electrolytes to wet the surface of La6.25Ga0.25La3ZrO12 (LLZO) pellets, enhancing wettability and reducing interfacial resistance. Cubic phase LLZO with a dense microstructure demonstrated excellent ionic conductivity of 1.53 mS/cm and a low activation energy of 0.268 eV, enabling efficient Li-ion transport. Symmetric cell studies revealed superior performance with ether-based electrolytes, achieving significantly lower interfacial resistance (~32 Ω⋅cm2) and a higher critical current density (0.6 mA/cm2) compared to carbonate-based systems. Long-term cycling tests confirmed stability of ether-based cells, maintaining over 1000 h of stable cycling at 0.1 mA/cm2. Full cells with LiFePO4​ (LFP) cathodes demonstrated excellent compatibility, retaining 78.5% capacity after 100 cycles with 99.9% Coulombic efficiency. These results underscore the potential of minimal liquid electrolyte usage as a scalable and cost-effective strategy to optimize the LLZO|Li interface for hybrid solid-state batteries.