Enhanced reversible sodium storage performance in CoFe₂O₄ nanoparticles as an anode material for sodium-ion batteries

Sodium (Na)-ion batteries are being pursued as viable alternatives to lithium (Li)-ion batteries because of their reasonable cost and enormous potential in application scale-up for energy storage systems in the future. However, it is difficult to identify electrode materials capable of accommodating the large ionic radius of Na-ions which makes Na-ion batteries exhibit slower intercalation kinetics than Li-ion batteries. Spinel ferrite is of interest because of its high theoretical capacity derived from multiple oxidation states. Herein, CoFe₂O₄ nanoparticles were successfully prepared using the ball milling technique, followed by calcination at 700℃ and 800℃ with varying calcination time. CoFe₂O₄ calcined at 700℃ for 2 h exhibited a uniform distribution of small particles (0.12 μm) and crystallites (45.89 nm). The electrode possesses high reversible capacity (178 mAh g⁻¹ at 0.1 C rate), reasonable cyclability (140 mAh g⁻¹ after 100 cycles) with 79% capacitive retention. The enhanced electrochemical performance of the CoFe₂O₄ electrode may be ascribed to its homogeneous distribution and fine particle size, which in turn decrease the Na-ion pathway and accelerate Na-ion transport within the electrode material.