Ionic Liquid-Acrylic Acid Copolymer Derived Nitrogen-Boron Codoped Carbon-Covered Na₃V₂(PO₄)₂F₃ as Cathode Material...

In this study, a nitrogen-boron codoped carbon layer, Na₃V₂(PO₄)₂F₃ sample, obtained by using an ionic liquid-acrylic acid copolymer as the nitrogen-boron source was used as the cathode material for sodium-ion batteries. The optimized and modified nitrogen and boron codoped carbon layer, Na₃V₂(PO₄)₂F₃ (denoted as NVPF-PCNB-20), illustrated better rate capability and cycling performance. The discharge capacities of NVPF-PCNB-20 at 0.5C and 10C were 109 and 90 mAh g^-1, respectively, and the capacity retention rate was 93.2% after 100 cycles at 0.5C and 92.8% after 750 cycles at 10C. Through in situ X-ray diffraction analysis of NVPF-PCNB-20, the results show that the modified Na₃V₂(PO₄)₂F₃ has excellent cycle reversibility. The scanning electron microscopy and transmission electron microscopy images reveal that NVPF-PCNB-20 particles were finer and covered by a uniform coating. The results show that the ionic liquid-acrylic acid copolymer not only make the material dispersion more uniform but also enhance the electronic conductivity and sodium storage performance of Na₃V₂(PO₄)₃F₃ effectively. This study may provide an effective way to synthesize nitrogen and boron codoped carbon-coated Na₃V₂(PO₄)₂F₃ with excellent electrochemical performance.