Sodium-ion batteries have emerged as a promising alternative to lithium-ion systems for large-scale energy storage due to the abundance and low cost of sodium resources. However, the development of high-capacity and structurally stable cathode materials remains a key challenge. In this work, mixed metal oxide cathodes with the composition Na₀.₆₇Fe₀.₅Mn₀.₅₋ ₓ M ₓ O₂ (M = Cu, Cr; x = 0.1, 0.3) were synthesized via a co-precipitation method. X-ray diffraction confirmed the formation of a P2-type hexagonal structure with P6₃/mmc symmetry, while morphological analysis revealed a well-defined layered architecture influenced by dopant concentration. To evaluate their potential for aqueous sodium-ion energy storage, electrochemical characterization was conducted within a narrow potential window of 0 – 0.4 V to suppress parasitic hydrogen and oxygen evolution side reactions. Under these conditions, the Na₀.₆₇Fe₀.₅Mn₀.₂Cu₀.₃O₂ electrode delivered an initial discharge capacity of 215.82 mAh g⁻¹ at 2250 mA/g and retained 173.98 mAh/g after 60 cycles, corresponding to a capacity retention of 80.62%. These results demonstrate that Cu substitution effectively enhances the electrochemical performance and cycling stability of P2-type NFM cathodes, highlighting their potential for aqueous sodium-ion storage applications.
Arif et al. (Wed,) studied this question.