Confronting Sulfur Electrode Passivation and Li Metal Electrode Degradation in Lithium-Sulfur Batteries Using Thiocyanate Anion

Abstract

Salt anions with a high donor number (DN) enable high sulfur utilization in lithium-sulfur (Li-S) batteries by inducing three-dimensional (3D) Li2S growth. However, their insufficient compatibility with Li metal electrodes limits their cycling stability. Herein, a new class of salt anion, thiocyanate (SCN−), is presented, which features a Janus character of electron donor and acceptor. Due to a strong Li+ coordination by SCN− and the direct interaction of SCN− with polysulfide anions, the LiSCN electrolyte has a remarkably high lithium polysulfide solubility. This electrolyte induces 3D Li2S formation and ameliorates cathode passivation, even more than Br−, a typical high DN anion. Moreover, SCN− forms a Li3N-enriched stable SEI layer at the surface of the Li metal electrode, enhancing cycling stability. A Li-S battery with the LiSCN electrolyte shows high current density operation (2.54 mA cm⁻2) with high discharge capacity (1133 mAh g⁻1) and prolonged cycle life (100 cycles). This work demonstrates that the cathode and anode performance in a Li-S battery can be simply and concurrently enhanced by the single salt anion.