Long‐Life Lithium‐Metal All‐Solid‐State Batteries and Stable Li Plating Enabled by In Situ Formation of Li3PS4 in the SEI Layer

Abstract An ultrastable and kinetically favorable interface is constructed between sulfide–poly(ethylene oxide) (PEO) composite solid electrolytes (CSEs) and lithium metal, via in situ formation of a solid electrolyte interphase (SEI) layer containing Li 3 PS 4 . A specially designed sulfide, lithium polysulfidophosphate (LPS), can distribute uniformly in the PEO matrix via a simple stirring process because of its complete solubility in acetonitrile solvent, which is advantageous for creating a homogeneous SEI layer. The CSE/Li interface with high Li + transportation capability is stabilized quickly through in situ formation of a Li 3 PS 4 /Li 2 S/LiF layer via the reaction between LPS and lithium metal to inhibit lithium dendrite growth. A Li/Li symmetric cell with the LPS‐integrated CSE exhibits constant and small CSE/Li resistance of 10 Ω cm 2 during cycling, delivering stable cycling for 3475 h at a current density of 0.2 mA cm −2 and a high critical current density of 0.9 mA cm −2 at 60 °C. Impressive electrochemical performance is also demonstrated for LiFePO 4 /CSE/Li all‐solid‐state batteries with capacity of 127.6 mAh g −1 after 1000 cycles at 1 C.