Mitigating the Jahn–Teller effect and enhancing the conductivity of O3-type NaNi1/3Fe1/3Mn1/3O2 cathode through Mn replacement with Sc for high-performance sodium-ion batteries

This study presents a novel modification strategy involving the replacement of Mn with Sc in the cathode of NaNi1/3Fe1/3Mn1/3O2 (NFM). The results of this study confirmed that Sc doping introduced strong Sc–O bonds to enhance the bonding between transition metal ions and O2−. Additionally, Sc doping reduced the proportion Mn3+ in the material (from 50.23% to 47.46%), thereby inhibiting the material structural distortion due to the Jahn–Teller effect induced by Mn3+. These factors were the main contributors to the improved cycling performance of the modified material. Furthermore, the introduction of Sc decreased the band gap of the material (1.7416–1.6706 eV) and the Na+ activation barrier energy (0.773–0.732 eV). These changes not noly facilitated the de-embedding of Na+ in the material lattice but also significantly enhanced the material electronic conductivity, leading to an excellent rate performance of the modified material. These results indicate that the NFM-Sc0.01 sample maintained an ultra-high capacity retention of 86.45% after 200 cycles at 1 C. At 5 C, the discharge capacity of NFM-Sc0.01 significantly increased from 79.3 mAh g−1 in NFM to 93.4 mAh g−1, demonstrating great potential for industrialized applications.