Construction of metal–organic framework-derived Al-doped Na₃V₂(PO₄)₃ cathode materials for high-performance rechargeable Na-ion batteries

Na₃V₂(PO₄)₃ (NVP) has emerged as one of the most promising cathode materials for sodium-ion batteries (SIBs) owing to its high ionic conductivity and high theoretical energy density. However, the inherent inferior conductivity of NVP prevents its achievement of the theoretical energy density even at low rates, thereby limiting the practical application of NVP in massive energy storage. Here, Al³⁺-doped Na₃V_2−xAl_x(PO₄)₃ (NVAP) materials derived from aluminum terephthalate (MIL-53(Al)) were synthesized for the first time, and the effects of Al³⁺ doping on the structural and electrochemical performances of NVP were investigated. The NVAP materials, particularly Na₃V_1.97Al_0.03(PO₄)₃ (NVAP2), exhibited superior cycling performance and rate capabilities compared with the NVP material. NVAP2 exhibited a good rate capability, with high reversible discharge capacities of 111.6, 110.3, 108.9, 106.6, 103.4, 96.9, and 88.7 mAh g⁻¹ at 0.1, 0.2, 0.5, 1, 2, 5, and 10C rates, respectively. Moreover, the NVAP2 material exhibited a prominent initial discharge capacity of 102.3 mAh g⁻¹ and maintained an excellent capacity retention rate of 92.0% after 2000 cycles at 10C, indicating significant cycling stability. Overall, this work provides an efficient technique for enhancing the electrochemical properties of cathode materials with a sodium superionic conductor structure for SIBs.