The effect of Na content on the electrochemical performance of the O3-type Na_xFe_0.5Mn_0.5O₂ for sodium-ion batteries

Owing to the abundant storage and environmentally benign of Na, Fe, and Mn elements, FeMn-based O3-type NaFe_0.5Mn_0.5O₂ materials were considered to be a promising cathode for sodium-ion batteries. However, the poor rate performance was barely satisfactory to the commercial production. Here, different Na content O3-type Na_xFe_0.5Mn_0.5O₂ (x = 1, 0.9, 0.8) for sodium-ion batteries were synthesized by solid-state reaction. The results illustrated that Na-deficient compound was beneficial to improve the rate performance and discharge capacity. Due to the Na-deficient in the octahedral sites, O3-type Na_0.8Fe_0.5Mn_0.5O₂ achieved a discharge capacity of 179 mAh g⁻¹ at 0.1 C, which is relatively higher than that of O3-type NaFe_0.5Mn_0.5O₂ (145 mAh g⁻¹). Besides, the O3-type Na_0.8Fe_0.5Mn_0.5O₂ exhibited an initial discharge capacity of 126 mAh g⁻¹ and outstanding capacity retention of 82.6% after 60 cycles at 1C. The excellent performance indicates that nontoxic and earth-abundant Na-deficient O3-type cathode may be a promising cathode for large-scale application and development of sodium-ion batteries.