Sodium-Ion Storage in Na₄VMn(PO₄)₃/C Porous Nanorods Electrode

Na₄VMn(PO₄)₃ (NVMP) is a prospective cathode for sodium-ion batteries (SIBs) due to its low cost and extraordinary structural stability. However, poor conductivity restricts the electrochemical performance of NVMP, which limits its development and application. Herein, carbon-encapsulated NVMP porous nanorods are prepared via a convenient electrospinning method. The prepared one-dimensional (1D) structure can effectively accelerate the transmission rate of electrons, and the porous structure of NVMP/C nanorods can increase the contact area between the electrolyte and electrode material, which can enhance the diffusion rate of sodium ions. Owing to this advantageous nanoarchitecture, the obtained NVMP/C porous nanorods delivered an initial reversible capacity of 90.9 mA h·g^-1 at 0.2 C and a discharge capacity of 68.0 mA h g^-1 at 5.0 C. NVMP/C can also achieve a good cycling stability with ideal capacity retentions of 90.4% and 89.8% after 800 cycles at 1 and 3 C, respectively. Moreover, even at a temperature of -30 °C at 0.3 C, the discharge capability was up to 40.1% of that at 20 °C, suggesting an impressive low-temperature tolerance. In situ X-ray diffraction demonstrated that there was no crystal distortion of the NVMP/C electrode during charge and discharge. This work can provide a high-performance strategy on modification of polyanion-positive electrode materials for SIBs.