In-situ synthesis of porous Na3V2(PO4)3 with stable V O C bridge bonding by hard template method

Low electronic conductivity and poor properties at high rate have hindered the application of Na₃V₂(PO₄)₃ (NVP). Herein, a facile synthesis of NVP with porous carbon skeleton is proposed. Specifically, Na₂CO₃ and glucose, acting as hard templates, are introduced to the precursors after initial firing stage, and Na₂CO₃ particles are removed by flushing after the final heatment. Due to the thermal conductivity of Na₂CO₃, the secondary addition of glucose can generate distinctive graphitized porous carbon skeleton, which bonds well with the amorphous carbon coating to construct stable and conductive network. The porous construction can alleviate the stress and strain caused by the current impact through deformation. Furthermore, ex-situ EIS reveals the highly conductive carbon skeleton can significantly reduce the surface resistance and result in an increase of effective voltage to promote the de-intercalation of Na⁺. Moreover, the ex-situ X-ray photoelectron spectroscopy (XPS) at different potentials confirms the stabilized existence of VOC bonds. Benefiting from the unique carbon skeleton, the PC-NVP releases capacity of 116.9 mAh g^-1 at 0.1C. Even at 120C, PC-NVP still exhibits a high capacity of 84.7 mAh g^-1, retaining a value of 41.3 mAh g^-1 after 16,000 cycles, corresponding to a low decay rate of 0.0032% per cycle.