Creating multi-electron reactions in a NASICON-type Na7V4(P2O7)4(PO4) cathode for sodium-ion batteries by activating reversible V4+/V5+ redox reactions

Abstract

Na₇V₄(P₂O₇)₄(PO₄) cathode materials with the advantage of superior cycling stability have been considered promising cathode candidates for sodium-ion batteries. However, their practical application is limited by low capacity and electronic conductivity. To address this issue, a Na₇V₄(P₂O₇)₄(PO₄)@NSC composite material was successfully synthesized by constructing an N/S co-doped carbon layer coating. N/S co-doping introduces abundant defects and active sites in carbon, boosting electronic conductivity. The formation of the C–S–V bond activates the V⁴⁺/V⁵⁺ redox process, which creates a multi-electron reaction and enhances capacity. The composite exhibits a capacity of 113.8 mAh g⁻¹ at 0.1C, which remains 80.8 mAh g⁻¹ even at 30C. The symmetric full battery retained 73.5% of its capacity after 1000 cycles at 5C. These results confirm the feasibility of N/S co-doping for NASICON-type cathodes, providing a modification strategy for subsequent research on exploiting the multielectron reaction characteristics of such NASICON cathodes.