Deciphering the synergistic roles of Fe-Cu-Mn in layered oxide cathodes for high-performance sodium-ion batteries

The Fe–Cu–Mn based layered oxides have gained considerable attention as particularly promising cathode materials for sodium-ion batteries (SIBs) due to their low cost, earth abundance, and favorable electrochemical properties. However, current research often treats this system as a unified matrix, which obscures the specific contributions of the individual Fe, Cu, and Mn components in determining structural stability and electrochemical performance. Herein, we systematically investigate the ternary Fe–Cu–Mn system without the addition of extraneous elements. By precisely tuning the stoichiometric ratios of Fe, Cu, and Mn within a Mn-rich layered framework, a direct correlation is established between composition, structure, and electrochemical behavior. It reveals that optimizing the Fe/Cu/Mn ratio effectively suppresses undesirable phase transitions, enhances structural stability, and results in superior electrochemical performance. The Na 0.70 Fe 0.15 Cu 0.15 Mn 0.70 O 2 (NFCM-0.70) cathode delivers a high initial energy density of 293.87 Wh kg −1 (based on the mass of the cathode) and presents the excellent capacity retention of 82.9% after 100 cycles at 0.2C. This work underscores the importance of rationally controlling intrinsic component ratios as a strategy for developing low-cost, high-performance layered oxide cathodes for SIBs.