Hard Carbon Wrapped Na₃V₂(PO₄)₃@C Porous Composite Extending Cycling Lifespan for Sodium-Ion Batteries

Although the NASICON-type of Na₃V₂(PO₄)₃ is regarded as a potential cathode candidate for advanced sodium-ion batteries (SIBs), it has an undesirable rate performance and low cyclability, which are a result of its poor electronic conductivity. Here, we utilized conductive polyaniline (PANI) grown in situ to obtain the hard carbon-coated porous Na₃V₂(PO₄)₃@C composite (NVP@C@HC) with a typically simple and effective sol–gel process. Based on the restriction of double carbon layers, the NVP size decreases distinctly, which can curtail the sodium-ion diffusion distance and enhance the electronic conductivity. As expected, the product displays good discharge capacity (111.6 mA h g^–1 at 1 C), outstanding rate capacity (60.4 mA h g^–1 at 50 C), and remarkable cycling stability (63.3 mA h g^–1 with a retention of 83.3% at 40 C over 3000 cycles). Also, it performs a long-term cycling capacity of 58.5 mA h g^–1 exceeding 15 000 cycles at 20 C (with a capacity loss of 0.24% per cycle).