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 poor Li/solid-state electrolyte (SSE) contact and Li infiltration within SSE due to local electronic conductivity at grain boundaries are major obstacles. Here, the interface chemistry of garnet-based SSEs is throughoutly 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-insulting interphase at the grain boundary to prevent Li filament growth inside garnet. The PPA-modified garnet electrolyte exhibit 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 for systematically regulating the electrolyte interface chemistry for solid-state batteries.
