Stabilizing NaCrO₂by Sodium Site Doping with Calcium

Layered cathode materials based on abundant, low cost raw materials have garnered interest in recent years. O3-type NaCrO 2 is a promising cathode material as it offers decent energy density and is easy to synthesize. In this study, calcium doped NaCrO 2 was synthesized using a solid-state method and the resulting [Na 1-2x Ca x ]CrO 2 materials were studied in sodium cells. Compared to calcium-free NaCrO 2 , [Na 0.9 Ca 0.05 ]CrO 2 has improved capacity retention without sacrificing reversible capacity. The enhanced performance was ascribed to structural stabilization of NaCrO 2 by Ca-doping, as observed by ex-situ X-ray diffraction. Finally, calcium doped NaCrO 2 was also found to have improved air-stability than the pristine material.