Long-Life Lithium-Metal All-Solid-State Batteries and Stable Li Plating Enabled by In Situ Formation of Li 3 PS 4 in the SEI Layer.

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.