Improving Cycling Stability of the Lithium Anode by a Spin-Coated High-Purity Li₃PS₄ Artificial SEI Layer

Controlling the composition and microstructure of the solid electrolyte interphase (SEI) layer is critical to improving the cycling stability of the high-energy-density lithium-metal electrode. It is a quite tricky task to control the properties of the SEI layer which is conventionally formed by the chemical reactions between a Li metal and the additives. Herein, we develop a new route to synthesize a lithium-compatible sol of the sulfide electrolyte Li₃PS₄, so that a Li₃PS₄ artificial SEI layer with a controllable nanoscale thickness and high phase purity can be prepared by spin-coating. The layer stabilizes the lithium/electrolyte interface by homogenizing the Li-ion flux, preventing the parasitic reactions, and alleviating concentration polarization. Consequently, a symmetrical cell with the Li₃PS₄-modified lithium electrodes can achieve stable lithium plating/stripping for 800 h at a current density of 1 mA cm^-2. The Li-S batteries assembled with the Li₃PS₄-protected Li anodes show better capacity retention than their bare Li counterparts, whose average decay rate from the 240th cycle to the 800th cycle is only 0.004%/cycle. In addition, the Li₃PS₄ layer improves the rate capacity of the batteries, significantly enhancing the capacity from 175 to 682 mA h g^-1 at a 2 C rate. The spin-coated Li₃PS₄ artificial SEI layer provides a new strategy to develop high-performance Li metal batteries.