Isomeric Organodithiol Additives for Improving Interfacial Chemistry in Rechargeable Li-S Batteries

Lithium-sulfur (Li-S) batteries have a high theoretical specific energy; however, their performance is plagued by the shuttle effect of lithium polysulfides and the instability of the lithium anode interface. Great efforts have been made using electrolyte additives to address the issues. Herein, we report a class of electrolyte additives, i.e., benzenedithiols (BDTs). Among the three isomers of BDTs, 1,4-BDT shows the best effect on the performance improvement of a Li-S battery because it can bond more sulfur atoms than the other two. The functionality of 1,4-BDT on the cathode and anode involves the chemical reactions of thiol groups. The S-S bonds were generated from 1,4-BDT and sulfur through oligomerization, which change the original redox path of sulfur and inhibit the shuttle effect of lithium polysulfides. In addition, 1,4-BDT can form a smooth and stable solid-electrolyte interphase (SEI), which can enable the Li/Li symmetric cell with an ultralow overpotential of 0.08 V at a high current density of 5 mA cm^-2 for over 300 h. The Li-S cell with 1,4-BDT displays the highest cycling stability at a C/5 rate, with an initial capacity of 1548.5 mAh g^-1 and a reversible capacity of 1306.9 mAh g^-1 after 200 cycles. The Li-S pouch cell with 1,4-BDT and 2.8 g of sulfur exhibits an initial capacity of 2640 mAh and a capacity retention rate of 84.2% after 26 cycles at a C/10 rate. This work demonstrates that organodithiol compounds can be used as functional electrolyte additives and provides a new direction to design materials for advanced Li-S batteries.