Reasonable design of a V₂O_5-x/TiO₂ active interface structure with high polysulfide adsorption energy for advanced lithium-sulfur batteries

A sulfur composite active material for lithium-sulfur batteries with a highly active interface structure can display excellent electrochemical performances. For this reason, in this paper, we design a type of V₂O_5-x/TiO₂ active interface structure with high polysulfide adsorption energy as a high-performance sulfur-wrapped matrix. Physical property characterization indicates this interface is constructed from circular anatase structure TiO₂ and anoxic vanadium oxide structure composed of V⁴⁺ and V⁵⁺. After sulfur wrapping, Ti-S and S-S bond structures are produced by chemical and physical adsorption. Density functional theory calculations show that the V₂O_5-x/TiO₂ interface has very high adsorption energy (-5.93 eV) with lithium polysulfide (Li₂S₆). After sulfur wrapping as a cathode active material, it displays low electrochemical charge transfer resistance (31.89 Ω) and high lithium-ion transfer efficiency (3.50 × 10⁻¹²). In addition, it has rather high discharge specific capacities of 1466.47, 963.84 and 801.16 mAh.g⁻¹ at 0.1, 0.2 and 0.5 C, respectively. After 500 cycles, the discharge capacity retention at 0.5 C is up to 76.11% corresponding to 0.048% capacity decay rate per cycle. This is the reason that the V₂O_5-x/TiO₂ active interface has very strong adsorption to polysulfide and can effectively suppress the shuttle effect (Q_low/Q_high=1.44 at 0.2 C).