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

The composite electrolyte of polyvinylidene fluoride (PVDF) and Li6.5La3Zr1.5Ta0.5O12 (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.