Enhancing electrochemical performance of O3-Type NaNi_0.4Fe_0.25Mn_0.35O₂ cathode materials in sodium-ion batteries via high-entropy strategy

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 Cu²⁺, Al³⁺, and Ti⁴⁺ ions into the pristine NaNi_0.4Fe_0.25Mn_0.35O₂ (NFM) structure, creating a new high-entropy NaNi_0.3Fe_0.1Mn_0.3Cu_0.1Al_0.05Ti_0.15O₂ (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.