Transforming Interface Chemistry throughout Garnet Electrolyte for Dendrite-Free Solid-State Batteries

Solid-state batteries have great potential for future energy storage because of their high energy density and enhanced safety. However, uneven Li plating/stripping due to a poor Li/solid-state electrolyte (SSE) contact and Li infiltration within the SSE due to local electronic conductivity at grain boundaries are major obstacles. Here, the interface chemistry of garnet-based SSEs is thoroughly transformed via the impregnation of polyphosphoric acid (PPA). The nanometer PPA coating not only acts as a lithiophilic and elastic interlayer for uniform Li cycling but also forms an electron-insulating interphase at the grain boundary to prevent Li filament growth inside the garnet. The PPA-modified garnet electrolyte exhibits an improved critical current density of 1.5 mA cm–2 and highly stable cell cycling for 2000 h at 0.2 mA cm–2 and 500 h at a high current density of 1 mA cm–2. Our work points out a way to systematically regulate the electrolyte interface chemistry for solid-state batteries.