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 lithiophobic nature. To address these issues, we applied small amounts of carbonate and ether-based liquid electrolytes to wet the surfaces of Li_6.25Ga_0.25La₃Zr₂O₁₂ (LLZO) pellets, enhancing wettability and reducing interfacial resistance. Cubic phase LLZO with a dense microstructure demonstrated an excellent ionic conductivity of 1.53 mS cm⁻¹ and a low activation energy of 0.268 eV, enabling efficient Li-ion transport. Symmetric cell studies revealed superior performance with ether-based electrolytes due to the formation of a Li₃N/LiF rich interphase, achieving a significantly lower interfacial resistance (∼32 Ω cm²) and a higher critical current density (0.6 mA cm⁻²) compared to carbonate-based systems. Long-term cycling tests confirmed the stability of ether-based cells, maintaining over 1000 h of stable cycling at 0.1 mA cm⁻². 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.