Tailoring the Boron Configurations in B-doped Na₃ V₂ (PO₄ )₃ @Carbon for Fast and Durable Sodium Storage

Na₃ V₂ (PO₄ )₃ (NVP) is a widely studied cathode material for sodium-ion batteries because of its high ionic conductivity and attractive charge/discharge plateau (3.4 V vs. Na/Na⁺ ). However, its poor electronic conductivity and severe volume expansion during sodium storage need to be addressed before its intensive application could be realized. Herein, boron-doped NVP was synthesized through a facile electrospinning method. By adding boric acid into the reaction mixture during electrospinning followed by carbonization, boron could be directly inserted into the carbon matrix, giving rise to B-doped carbon nanofiber wrapped NVP. By tuning the doping amount, the boron-containing configurations could be facilely manipulated, playing different roles in promoting the sodium storage properties of the composite. Based on the calculation results, BC₂ O enhanced sodium diffusion by lowering the energy barrier, while BCO₂ improved the structural stability. Due to these specific functionalities of the configurations, the as-prepared composite with a balanced amount of BC₂ O and BCO₂ demonstrated superior sodium storage capacity of 113 mAh g^-1 at 1 C, outstanding long cycling performance of 103 mAh g^-1 at 10 C, and retained 91 mAh g^-1 after 1500 cycles. This gave rise to a capacity loss of only 0.08‰ per cycle, much better than the undoped counterpart.