Electrochemical investigations of a high-capacity Na₂CrO₄/C nanocomposite anode for sodium-ion batteries

Majority of the anodes in sodium-ion batteries (SIBs) show low working voltage which prevents long cycling due to formation of plating. In this study, Na₂CrO₄/C has employed a relatively high working voltage (~1 V) anode for SIBs. The nanocomposite of Na₂CrO₄ and highly conducting super P carbon is synthesized using the ball mill method for high-performance SIBs. X-ray diffraction (XRD) graphs show a decrease in the peak intensity and expansion of full-width half-maximum which results in reduced size of the nanocomposite. Scanning electron microscopy further confirms the reduction of size from micro to the nanometer range. The Na₂CrO₄/C nanocomposite shows a specific capacity of 228 mAh g⁻¹ at 0.1 C rate during the initial cycle and 166 mAh g⁻¹ during the 100th cycle. The Na₂CrO₄/C nanocomposite exhibits a specific capacity of 71 mAh g⁻¹ at an elevated rate of 2.0 C. The structure of Na₂CrO₄/C nanocomposite is elucidated using in situ XRD and the outcomes show the transformation of material from crystalline to amorphous phase during cycling. X-ray absorption spectroscopy is employed to follow the oxidation/reduction change of Cr in the Na₂CrO₄/C nanocomposite.