Improving the Electrochemical Performance of Layered Oxide Cathodes via Fluorine Anion Doping and Medium-Entropy Configuration Design

In order to address the challenges of irreversible phase transition and oxygen depletion in cathode materials during charge–discharge cycling of sodium-ion batteries (SIBs), we develop a dual modification strategy combining a medium-entropy design of transition metal (TM) layers and anion doping. The optimized cathode material, Na0.63Ni0.1Fe0.2Mg0.1Cu0.1Mn0.5O1.9F0.1 (NNFMCM-F), has a medium-entropy TM layer configuration, thereby enhancing structural stability. Meanwhile, fluorine anion doping enhances the anionic interactions in the TM layer and adjusts the elemental valence state, which enlarges the interlayer spacing and improves the Na+ migration rate. In addition, F– doping can effectively inhibit the Jahn–Teller aberration and activate the oxygen redox reaction, thus synergistically improving the specific capacity and cycling stability. The results show that the modified NNFMCM-F has an initial discharge capacity of 176.41 mA h g–1 at 0.1 C (1.5–4.3 V) and a capacity retention rate of 85.08% after 100 cycles, which is superior to that of the conventional SIB layered oxide cathode materials.