Simultaneous Mn and Cl doping on Na₃V₂(PO₄)₃ with high performance for full sodium-ion batteries

Nowadays, the poor conductivity and unstable structure have become obstacles for the popularization of Na₃V₂(PO₄)₃ (NVP). In the current work, a dual-modified Mn_0.1Cl_0.3-NVP composite doped with Mn and Cl is prepared by a facile sol-gel method. When Mn²⁺ with a large ionic radius replaces small V³⁺, it can improve the stability of the NVP crystal structure. In addition, the replacement of V³⁺ by Mn²⁺ in a low valence state can generate redundant hole carriers, which is conducive to the rapid transport of electrons. The substitution of PO₄^3- by Cl^-, which is more electronegative, can reduce the impedance and facilitate the movement of Na⁺. Owing to the synergistic effect of Mn and Cl co-substitution, the structural stability of NVP was systematically enhanced, and the electron transfer and ion diffusion were effectively improved. Consequently, the optimized Mn_0.1Cl_0.3-NVP sample demonstrated superior electrochemical performance and kinetic properties. It exhibited a high reversible capacity of 109.2 mA h g^-1 at 0.1C. Even at 15 and 30C, high discharge capacities of 70.3 mA h g^-1 and 68.2 mA h g^-1 were observed after 2000 cycles with capacity retention above 80%. Moreover, it delivered remarkable capacities of 77.1 and 73.4 mA h g^-1 at 100 and 200C with retained capacity values of 50.3 and 47 mA h g^-1, respectively, after 2000 cycles. Furthermore, the assembled Mn_0.1Cl_0.3-NVP//HC full cell delivered a high value of 94.7 mA h g^-1 and lit LED bulbs, indicating its excellent application potential.