Sulfydryl-modified MXene as a sulfur host for highly stable Li-S batteries

As a novel two-dimensional (2D) layered material, Ti 3 C 2 T x MXene has excellent electronic conductivity and strong polysulfides adsorption. Its potential for Li-S batteries has been well recoginised since it can compensate conductivity of sulfur and improve cycling stability simultaneously. However, like other 2D materials , the stacking feature of the MXene nanosheet greatly limits its advantages and applications. Herein, a sulfydryl-modified MXene - sulfur cathode is synthesized via simple hydrothermal and copolymerization reactions. Compared to the conventional physical absorption between MXene and polysulfide, it was found that a chemical modification of MXene offers a much robust structure with little stacking on MXene. During the discharge process high-order Li 2 S 4 intermediates were first formed but consumed immediately. The remaining polysulfides are only short chains of Li 2 S, Li 2 S 2 and Li 2 S 3 . This type of cathode can greatly suppress the “shuttle effect” by reducing the generation of soluble high-order polysulfides in the electrolyte, which is attributed to rapid capacity fading. As a result, the cathode achieves an excellent initial specific capacity of 1367 mAh·g −1 at 0.1 C. It also has a high first capacity of 880 mAh·g −1 and remains 715 mAh·g −1 after 500 cycles at 1 C, with a retention rate of 81.3%. Our work provides a new strategy for applying MXene in the Li-S battery field.