Sm3+ doped Na3V2-xSmx(PO4)3@C cathode for high-performance sodium ion batteries: Towards optimized sodium storage kinetics and cycling stability

Na₃V₂(PO₄)₃ is considered a promising cathode material for high-performance sodium ion batteries due to its high operating voltage, fast ion diffusion and exceptionally stable crystal structure. However, its low intrinsic electronic conductivity remains a challenge for large-scale applications. In this study, a Sm³⁺-doped strategy is proposed to enhance its high-rate capacity and cycling stability. Theoretical calculations and charge transfer kinetics tests demonstrate that Sm³⁺ doping can reduce the band gap and Na⁺ diffusion energy barrier, thereby effectively enhancing electron conduction and Na⁺ migration. Moreover, the reduced integrated-crystal orbital Hamilton population (ICOHP) of Sm-O bond indicates improved structural stability of the crystal structure. Consequently, the synthesized Sm0.05-NVP@C exhibits outstanding rate capacities and cycling stabilities, delivering excellent reversible capacities of 103.26 and 72.81mAh g⁻¹ at 1C and 40C. Moreover, it demonstrates remarkable capacity retention of 92.56 % at 10C after 1250 cycles. Notably, in-situ XRD reveals a highly reversible bi-phase transition reaction mechanism between Na₃V_1.95Sm_0.05(PO₄)₃ and NaV_1.95Sm_0.05(PO₄)₃. This study highlights the great potential of Na₃V₂(PO₄)₃ cathode for achieving high-rate performance and long-term stability in sodium-ion batteries.