Lithium metal protection through in-situ formed solid electrolyte interphase in lithium-sulfur batteries: The role of polysulfides on lithium anode

The dissolution and diffusion of Li polysulfide (LiPS) intermediates are regarded as one of the most serious problems for capacity decay and cell failure of lithium-sulfur (Li-S) batteries. Herein we proposed a failure mechanism of Li metal anode in Li-S cells based on the mechanistic investigation into the complex interactions between LiPSs and Li metal. The LiPSs participate the formation of inorganic layers in the solid electrolyte interphase (SEI) in a LiPS-LiNO₃ containing ether-based electrolyte. Li metal anode is well protected by the stable inorganic layer in-situ formed in an electrolyte containing 0.020 M Li₂S₅ (0.10 M sulfur) and 5.0 wt % LiNO₃. The metal anode with LiF-Li₂S_x riched SEI rendered a stable Coulombic efficiency of 95% after 233 cycles for Li-Cu half cells. A dendrite-free morphology of Li metal anode is observed under the harsh condition. When the LiPS is with a very high concentration of higher than 0.50 M sulfur in the organic electrolyte, the in-situ formed SEI cannot well maintain and the Li metal is gradually etched. Therefore, the polysulfide dissolution and diffusion should be delicately regulated to render a practical Li-S cell when the areal sulfur loading is high.