Off-stoichiometric Na V (PO)/C nanocomposites as cathode materials for high-performance sodium-ion batteries prepared by high-energy ball milling.

NaV(PO) (NVP) is regarded as a promising cathode material for sustainable energy storage applications. Here we present an efficient method to synthesize off-stoichiometric Na V (PO)/C ( = 0-0.10) nanocomposites with excellent high-rate and long-life performance for sodium-ion batteries by high-energy ball milling. It is found that Na V (PO)/C nanocomposites with = 0.05 (NVP-0.05) exhibit the most excellent performance. When cycled at a rate of 1C in the range of 2.3-3.9 V, the initial discharge capacity of NVP-0.05 is 112.4 mA h g, which is about 96% of its theoretical value (117.6 mA h g). Even at 20C, it still delivers a discharge capacity of 92.3 mA h g (79% of the theoretical capacity). The specific capacity of NVP-0.05 is as high as 100.7 mA h g after 500 cycles at 5C, which maintains 95% of its initial value (106 mA h g). The significantly improved electrochemical performance of NVP-0.05 is attributed to the decrease of internal resistance and increase of the Na ion diffusion coefficient.