Reconfiguring Organosulfur Cathode by Over-Lithiation to Enable Ultrathick Lithium Metal Anode toward Practical Lithium-Sulfur Batteries.

Abstract

An ultrathick lithium metal anode (LMA) is a prerequisite for developing practical lithium-sulfur (Li-S) batteries that simultaneously meet the requirements of high areal capacity, lean electrolyte, and limited excess Li. Inspired by the electrochemical process for an organosulfur cathode, herein, we reconfigure such a sulfur cathode by using an overlithiation strategy to enable the formation of a high performance LMA. Specifically, an applicable ultrathick LMA is successfully constructed by overlithiating a well-known organosulfur cathode material, sulfurized polyacrylonitrile (SPAN). SPAN contains a polymeric pyridine structure with an outstanding lithium-ion affinity, so that it can act as a lithiophilic matrix. More importantly, a Li₂S-rich solid electrolyte interphase (SEI) can be generated on the surface of SPAN during the overlithiation process. The synergistic effect of the lithiophilic matrix and a robust SEI leads to a dense deposition of lithium, which enables one to form an ultrathick LMA (159 μm, 30 mAh cm^-2) with high Coulombic efficiency (99.7%). Such an LMA paired with a sulfur cathode of high areal capacity (up to 16 mAh cm^-2) shows stable cycling under practical conditions of a lean electrolyte (2.2 μL mg_S^-1) and a negative-to-positive capacity (N/P) ratio as low as 1.3. The applicability of the ultrathick LMA was further verified with Li-S pouch cells, indicating a highly prospective route toward realization of practical Li-S batteries.