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

As a novel two-dimensional (2D) layered material, Ti3C2Tx 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 Li2S4 intermediates were first formed but consumed immediately. The remaining polysulfides are only short chains of Li2S, Li2S2 and Li2S3. 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.