Bifunctional Interphase-Enabled Li₁₀GeP₂S₁₂ Electrolytes for Lithium–Sulfur Battery

Li10GeP2S12 (LGPS) has a high ionic conductivity and compatibility with sulfur cathodes; however, the instability of LGPS against Li and Li dendrite growth still remains unsolved. Here, we solved these two challenges by forming a lithiophilic–lithiophobic gradient interlayer interphase layer between Li and LGPS through the sequential reduction of salts and solvent in Mg(TFSI)2-LiTFSI-DME liquid electrolyte at the LGPS/Li interface (TFSI = bis(trifluoromethanesulfonyl)imide; DME = dimethoxyethane). Mg(TFSI)2-LiTFSI is first reduced, forming a lithiophilic LixMg alloy-rich layer on the lithium surface and a lithiophobic LiF-rich layer on top of LixMg due to the lithiophobicity difference. The later reduced DME solvent forms a flexible organic polymer between the LiF-rich layer and LGPS. After evaporation of DME solvent, the Li/LGPS/Ni-Li2S-LiTiS2 all-solid-state battery shows a reversible capacity of 699.7 mAh g–1 (1.07 mAh cm–2) based on the mass of Ni-Li2S-LiTiS2 at 100 mA g–1 (0.26 mA cm–2). The rational design of a solid electrolyte interface between a Li anode and LGPS electrolyte opens a new opportunity to develop high-performance all-solid-state lithium batteries.