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

Salt anions with a high donor number (DN) enable high sulfur utilization in lithium‐sulfur (Li‐S) batteries by inducing three‐dimensional (3D) Li(2)S 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 Li(2)S formation and ameliorates cathode passivation, even more than Br(−), a typical high DN anion. Moreover, SCN(−) forms a Li(3)N‐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.