Constructing a stable interface between the sulfide electrolyte and the Li metal anode via a Li+-conductive gel polymer interlayerElectronic supplementary information (ESI) available: Experimental section, materials characterization, electrochemical measurements, the specific values of resistances and the calculation result of ionic conductivity of Fig. 2b, Fig. S1b, detailed equivalent circuit of Fig. 2b and 4c, d, EIS spectrum of GPI-LGPS-GPI composite electrolytes, the EDS elemental mapping images of Li anode in Li|LGPS|Li system after 30 cycles, Li plating/stripping profiles of Li|LGPS|Li cells of 0.5 mA cm−2 for 0.5 mA h cm−2 at room temperature, F 1s, C 1s XPS spectrum of the cycled Li anode and LGPS pellet recovered from Li|GPI–LGPS–GPI|Li battery, and XPS binding energies with attributed species shown in Fig. 5 and Fig. S7, S8. See DOI: 10.1039/d1qm00395j