Mechanically Exfoliated Graphite for Highly Reversible Na-Storage with Carbon Coated NaV(PO) Cathode with Low-Temperature Conditions.

Tremendous efforts are put forward to develop novel high-performance electrodes for Na-ion batteries (SIBs) in order to replace commercial Li-ion batteries (LIBs). Graphite, the most versatile anode for LIBs, fails to accommodate Naions owing to the poor thermodynamic stability of the binary graphite intercalation compound. This study aims to exfoliate the layers of graphite through a simple mechanical process at different time intervals (1, 5, 10, 20, 40, and 80 h) and examine the potential candidate for Na-storage in the presence of carbonate-based electrolytes. This study reports that ball milling plays a vital role in the performance of the graphite in Na-storage. The graphite exfoliated for 80 h (EG-80h) rendered an excellent reversible capacity of 209 mAh g with coulombic efficiency of >99% after 100 cycles in EC-based electrolyte. In situ impedance analysis is performed to validate the charge storage mechanism and Na-ion kinetics. The performance of EG-80h in a full-cell assembly is evaluated with a carbon-coated NaV(PO) cathode, which exhibited an initial capacity of ≈75 mAh g and energy density of 201 Wh kg. In addition, the adaptability of the NVPC/EG-80h cell at different temperatures is examined from -10 to 50 °C, displaying excellent performance in both high and low-temperature conditions.