Enhancing electrochemical performance of O3-Type NaNi0.4Fe0.25Mn0.35O2 cathode materials in sodium-ion batteries via high-entropy strategy

• A novel high-entropy NaNi 0.3 Fe 0.1 Mn 0.3 Cu 0.1 Al 0.05 Ti 0.15 O 2 (NFMCAT) cathode was developed for enhanced performance. • NFMCAT effectively suppressed undesirable phase transitions, even under high voltage conditions. • NFMCAT demonstrates superior cycling stability and rate capability due to enhanced Na⁺ kinetic performance. • In situ XRD verified the mitigation of lattice parameter changes in NFMCAT, ensuring improved structural stability. • NFMCAT exhibited excellent performance in full cell tests, confirming its practical applicability. Sodium-ion battery (SIB) cathodes with an O3-type layered structure exhibit promising theoretical capacity and affordability. However, their poor cycling stability, caused by undesired phase transitions and structural instability during cycling, limits their practical application. To overcome these challenges, we implement a high-entropy strategy by incorporating Cu 2+ , Al 3+ , and Ti 4+ ions into the pristine NaNi 0.4 Fe 0.25 Mn 0.35 O 2 (NFM) structure, creating a new high-entropy NaNi 0.3 Fe 0.1 Mn 0.3 Cu 0.1 Al 0.05 Ti 0.15 O 2 (NFMCAT) cathode. Electrochemical tests show that NFMCAT achieves a first discharge capacity of 134.6 mAh g −1 at 0.1C, retaining 88% of its capacity after 200 cycles at 2C. Improved Na + diffusion dynamics are demonstrated through GITT, CV, and EIS analyses. Additionally, in situ X-ray diffraction confirms reduced lattice strain during phase transitions. Full-cell evaluations using a hard carbon anode showcase excellent rate capability and durability, retaining approximately 73.2% of its capacity after 500 cycles at 2C. This research highlights the potential of high-entropy modification for developing stable, high-performance cathode materials to enhance the performance of SIBs.