Enhanced Bulk and Interfacial Conductivity in All-Solid-State Lithium Metal Batteries via Garnet Surface Phosphorylation

The composite electrolyte of polyvinylidene fluoride (PVDF) and Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZO) is considered one of the most promising electrolytes for next-generation lithium batteries. However, the presence of Li₂CO₃ on the LLZO surface reduces conductivity and leads to PVDF chain cross-linking. In this study, H₃PO₄ is used to remove the alkaline Li₂CO₃ layer, and the effect of residual Li₃PO₄ on bulk conductivity and lithium metal interface conduction is investigated. The phosphorylation of the LLZO surface enhances ion transport channels, increasing ionic conductivity to 5.06 × 10^-4 S cm^-1. Notably, Li₃PO₄ catalyzes the decomposition of LiFSI, facilitating the formation of abundant inorganic compounds with rapid lithium-ion diffusion capability such as Li₃N, LiF and Li₂S₂O₇, which increases the interfacial exchange current density of lithium symmetric batteries by approximately 3.5 times. Additionally, a Li||LFP battery achieved 89% capacity retention after 400 cycles at 1C. These results demonstrate a promising strategy for developing commercial solid-state electrolytes for all-solid-state lithium metal batteries.