Construction of metal–organic framework-derived Al-doped Na 3V 2(PO 4) 3 cathode materials for high-performance rechargeable Na-ion batteries

Na₃V₂(PO₄)₃ (NVP) was emerged as one of the most promising cathode materials for sodium ion batteries (SIBs) owing to the high ionic conductivity, and high theoretical energy density. Nevertheless, the inherent inferior conductivity of NVP prevents its achievement of the theoretical energy density even at low rates, thus limiting its practical application in massive energy storage. Here, Al³⁺-doped Na₃V_2-xAl_x(PO₄)₃ (NVAP) materials derived from aluminum terephthalate (MIL-53(Al)) have been synthesized for the first time, and the impacts of Al³⁺ doping on the structural and electrochemical performance of NVP have been investigated. It can be found that the NVAP materials have superior cycling and rate capabilities compared with the NVP material, especially the Na₃V_1.97Al_0.03(PO₄)₃ (NVAP2) material. The NVAP2 indicates a good rate property with a high reversible discharge capacity 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. The NVAP2 provides a prominent initial discharge capacity of 102.3 mAh g^-1 and maintains an excellent capacity retention rate of 92.0% after 2000 cycles even at 10C, indicating significant cycling stability. This work provides an efficient way to enhance the electrochemical property of sodium superionic conductors structured cathode materials of SIBs.