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.