Electrochemical Improvement of Na_0.62K_0.05Mg_2/9Cu_1/9Mn_2/3O₂ P2-Type Layer-Oxide Anionic Redox Cathodes of Sodium-Ion Batteries via Incorporating K-Doping

Sodium-ion batteries with P2-type layered transition metal oxides (NaxTMO2) as cathode materials hold promise for large-scale energy storage due to their cost-effectiveness and high operating voltage. However, achieving the theoretical capacity is challenging due to the limitations of the electrode materials. To overcome this challenge, a K-doped Na0.67Mg2/9Mn2/3Cu1/9O2 cathode material was developed in this study to enhance the electrochemical performance and suppress structural evolution. Synthesized via a sol–gel method, Na0.62K0.05Mg2/9Mn2/3Cu1/9O2 exhibited a superb capacity of 203 mAh g–1 compared to 185 mAh g–1 exhibited by its pristine material. X-ray photoelectron spectroscopy confirmed that oxygen was involved in the electrochemical reactions occurring at high voltage, while operando synchrotron X-ray diffraction showed no P2–O2 structural evolution that occurred during battery cycling. This approach demonstrates the feasibility of using cationic doping to enhance the cycling stability of sodium-ion battery cathodes and their anionic redox potentials for increasing battery capacities, offering new opportunities for the use of high-performance cathode materials in large-scale energy storage systems.