Blocking Polysulfide with Co2B@CNT via "Synergetic Adsorptive Effect" toward Ultrahigh-Rate Capability and Robust Lithium-Sulfur Battery.

Li-S batteries have attracted great interest as the next-generation secondary batteries due to their high energy density, being environmentally friendly, and low price. However, the road to commercialization of lithium-sulfur batteries remains limited owing to the "shuttle effect" of soluble polysulfides, which results in the inferior cycle stability. Herein, a potent functional separator is developed to restrain the "shuttle effect" by coating Co2B@carbon nanotube layer on the commercialized polypropylene separator. In merits of the coadsorption of Co sites and B sites, such Co2B shows highly efficient polysulfides block (11.67 mg/m2 for Li2S6). Besides, the composite also exhibits obviously catalysis from Li2S8 to Li2S. By combining the fast electron transportation along the carbon nanotube, a superior rate performance is achieved with the modified separator and common carbon-sulfur cathode. Typically, the cell with Co2B@CNT shows prominent cycling life with a capacity degradation of 0.0072% per cycle (3000 cycles) and ultrahigh-rate capability at 5 C current (1172.8 mAh/g), which outstands the previously reported polysulfides barrier layer. The cell with Co2B@CNT can exhibit electrochemical performance at areal capacity of 5.5 mAh/cm2 (0.5 C) when the sulfur loading increased to 5.8 mg/cm2. This work defines an efficacious strategy to restrain the "shuttle effect" of polysulfides and shed light on the great potential of borides in Li-S battery.