Shortening the Reaction Pathway of Sulfur Redox Kinetics with 2,5-Dichloro-1,4-Benzoquinone to Minimize the Shuttle Effect in Lithium–Sulfur Batteries

The low active material utilization, sluggish sulfur redox kinetics, and formation of unstable interfacial layers remain critical challenges in lithium–sulfur (Li–S) batteries. To minimize these effects, 2, 5-dichloro-1,4-benzoquinone (DCBQ) was demonstrated in this study as an electrolyte additive. Leveraging its unique symmetrical structure, DCBQ interacted with polysulfides during charge and discharge cycles to form insoluble symmetric cyclic organic polysulfide intermediates. These intermediates served as a cathode-electrolyte interphase (CEI) by attaching to the sulfur cathode surface, which mitigated the shuttle effect by reducing the accumulation of insoluble Li₂S and suppressing polysulfide dissolution. In the presence of DCBQ, the discharge pathway for Li₂S₆ transitioned from Li₂S₆ → Li₂S₄ → Li₂S₂ → Li₂S to a shortened sequence of Li₂S₆ → Li₂S₃ → Li₂S, enhancing sulfur utilization and streamlining redox processes. On the anode side, the formation of LiCl and intermediate compounds contributed to an organic–inorganic solid-electrolyte interface (SEI), which protected the lithium anode, improved the Li⁺ diffusion coefficient (6.63 × 10^–11 cm² S^–1), and eventually enhanced the battery’s cycling stability. Consequently, the Li–S battery that included the DCBQ additive exhibited nearly 100% Coulombic efficiency at a rate of 0.2 C. It showed an initial discharge-specific capacity of 992.24 mAh g^–1 and experienced a low-capacity degradation of just 0.45% per cycle over 120 cycles. These results highlight the effectiveness of DCBQ as an electrolyte additive in enhancing both the performance and stability of the battery.