Microstructure tuned NaV(PO)@C electrodes toward ultra-long-life sodium-ion batteries.

Sodium-ion batteries (SIBs) are emerging as the best replacement for Li-ion batteries. In this regard, research on developing a reliable cathode material for SIBs is burgeoning. Rhombohedral NaV(PO) (NVP), is a typical sodium super ionic conductor (NASICON) type material having prominent usage as a cathode material for SIBs. In this study, we prepared an NVP@C composite using a one-step hydrothermal method (at 180 °C) and consecutively calcined at different temperatures (750, 800, 850, and 900 °C). All the samples were thoroughly characterized and the changes in the crystal structure and particle size distribution were investigated using a Rietveld refinement method. NVP calcined at 850 °C exhibits the best battery performance with a discharge capacity of 94 mA h g and retention up to 90% after 250 cycles at 2C. It also exhibits remarkable cycling stability with 94% (63 mA h g) retention after 2000 cycles at high-rate endurance (10C). The observed electrochemical performances of the samples were correlated with improved electrical conductivity due to the conductive carbon mixing with NaV(PO) and enhancement in the crystallinity.