Rate Performance Enhancement in Borate-Substituted Na₃V₂O₂(PO₄)_2–<i>x</i>(BO₃)_<i>x</i>F Polyanionic Cathode Materials for Sodium Storage

The NASICON-type cathode material, sodium vanadium phosphate Na3V2(PO4)2O2F (NVOPF), is considered to be a promising cathode material for sodium-ion batteries due to its high operating voltage, energy density, and structural stability. However, its application is limited by its slow reaction kinetics due to low intrinsic electronic conductivity. In the present work, part of polyanionic PO43– is replaced by BO33–, and the resulting Na3V2O2(PO4)1.9(BO3)0.1F (NVOPFB0.1) has demonstrated excellent rate capability, with a specific capacity of 75.9 mAh g–1 at a high current rate of 40C, while at its normal rate (0.2C), the capacity is 128.8 mAh g–1. Cycle test of the cathode material shows that after 5000 cycles at 10C, the capacity can still retain 66.7% from its initial value.