In-situ construction of a Mg-modified interface to guide uniform lithium deposition for stable all-solid-state batteries

Abstract Uniform lithium deposition in all-solid-state Li metal batteries is greatly influenced by the anode/electrolyte interface. Herein, a Mg-modified interface was constructed via the simple in-situ electrochemical reduction of Mg2+ from Mg(TFSI)2 in polyethylene oxide (PEO) and a Li bis(trifluoromethane)sulfonimide (LiTFSI) formulae. As confirmed by cryogenic transmission electron microscopy, the anode/electrolyte interface exhibited hybrids consisting of crystalline Mg, Li2O, and Li dots embedded in an amorphous polymer electrolyte. The crystalline Mg dots guided the uniform Li nucleation and growth, inducing a smoother anode/electrolyte interface compared with the pristine electrolyte. With 1 wt% Mg(TFSI)2 in the PEO-LiTFSI electrolyte, the Mg-modified electrolyte enabled the Li/Li symmetric cells with cycling performance of over 1700 and 1400 h at current densities of 0.1 and 0.2 mA cm-2, respectively. Moreover, the full LFP/Li cells using the novel Mg-modified electrolyte delivered a cycling lifespan of over 450 cycles with negligible capacity loss.