Cobalt/MXene-derived TiO₂ heterostructure as a functional separator coating to trap polysulfide and accelerate redox kinetics for reliable lithium-sulfur battery

Lithium-sulfur (Li-S) batteries are one of the most potential new energy storage systems due to their high theoretical capacity (1675 mAh g(-1)) and high energy density (2600 Wh kg(-1)). However, the application of Li-S batteries is currently restricted due to the dissolution of polysulfides in the electrolyte, which leads to the shuttle effect of lithium polysulfides (LiPSs). Here, we present a Co@MXene-derived TiO2 heterostructure decorated on carbon sheets derived from folic acid (Co@M-TiO2/C) as a functional separator coating to trap polysulfide and accelerate redox kinetics in Li-S batteries. The interconnected porous structure with good electrical conductivity of the heterostructure boasts rapid ion diffusion and efficient electron transfer within the battery. By attaching Co and MXene-derived dual-phased TiO2 to two-dimensional carbon sheets, heterostructures are formed, ensuring complete exposure of the active sites. These heterostructures exhibit catalytic effects on LiPSs and excellent adsorption capabilities, effectively inhibiting the shuttle effect and accelerating the redox kinetics. Considering these advantages, the Li-S battery with the optimized Co@M-TiO2/C modified separator demonstrates a high specific capacity of 1481.7 mAh g(-1) at 0.2 C, superior rate performance of 855.5 mAh g(-1) at 2 C, and excellent cycling performance under a high sulfur load of 4.4 mg cm(-2).