Molten Salt Thermal Treatment Synthesis of S-Doped V2CTx and Its Performance as a Cathode in Aqueous Zn-Ion Batteries

The lack of suitable cathode materials with a high capacity and good stability is a crucial problem affecting the development of aqueous Zn-ion batteries. Herein, a novel strategy for the modification of V₂CT_x through molten salt thermal treatment is proposed. In the novel route, S heteroatoms were introduced into V₂CT_x through a substitution reaction during the dissolution of Li₂S in LiCl-KCl molten salts. Then, surface V₂O₅ was obtained through the in situ electrochemical charging/discharging of the S-doped V₂CT_x (MS-S-V₂CT_x) cathode. The assembled Zn/MS-S-V₂CT_x battery showed a high reversible discharge capacity of 411.3 mAh g^-1 at a current density of 0.5 A g^-1, an 80% capacitance retention after long cycle stability tests at 10 A g^-1 for 3000 cycles, and a high energy density of 375.5 Wh kg^-1 in 2M ZnSO₄. Density functional theory calculations demonstrate that the improved electrochemical performance of the cathode can be attributed to the introduced S heteroatoms, which considerably reduced the ion diffusion energy barrier for Zn²⁺ ions and improved the stability of V₂O₅. This work provides a novel method to produce highly active and stable vanadium-based cathodes for aqueous Zn-ion batteries.