Synergistic effect of multi-transition metal co-substitution in high cycle life performance of NaxCo0.5Fe0.25Mn0.25O2 cathode for sodium-ion batteries

Abstract

In this work, multi-transition metal co-substituted NaxCo0.5Fe0.25Mn0.25O2 is synthesized through a solid-state method using a two-step heating approach and its physicochemical and electrochemical features as a cathode material for sodium-ion batteries (SIBs) are studied. Various advanced physicochemical characterization studies reveal the P3 structure of the as-prepared NaxCo0.5Fe0.25Mn0.25O2 possessing multiple crystal symmetries with high-order crystallinity, suitable for enhanced Na+-ion intercalation and deintercalation. Its electrochemical performances are investigated with the fabricated Na/1 M-NaClO4/NaxCo0.5Fe0.25Mn0.25O2 coin cells. The cyclic voltammetry study reveals that the redox process of the cathode material is due to the M3+/M4+ (where M = Co0.5Fe0.25Mn0.25) redox couple with excellent structural reversibility during the charging/discharging process. The electrochemical impedance spectroscopy analysis suggests excellent compatibility of the electrolyte with the cathode, showing a good state of health, a low value of resistance offered to the cell, and a very negligible value of double-layer capacitance. The galvanostatic charge-discharge interpretations reveal that NaxCo0.5Fe0.25Mn0.25O2 delivers significant rate capability and a high discharge capacity of 94.22 mA h g−1 at 0.05C by maintaining stable performance across a range of C-rates. The material exhibits high coulombic efficiency and impressive energy densities, with a maximum discharge energy density of 279.82 W h kg−1 at 0.05C. Notably, NaxCo0.5Fe0.25Mn0.25O2 demonstrates excellent cycle life, retaining 92.2, 78.4, 53.9, 39.4, and 28.3% of the initial discharge capacity at the 100th, 200th, 300th, 400th, and 500th cycles, respectively, owing to the synergistic effect of co-substituted multi-transition metals. © 2025 The Royal Society of Chemistry.