Promoting configurational entropy and structure stability of O3-type layered oxide cathodes via Fe regulation for sodium-ion batteries

O3-type Ni-Mn-based layered oxides as cathode materials have received much attention due to their high theoretical capacity in sodium-ion batteries (SIBs). However, the occurrence of irreversible phase transition during the charge-discharge process will lead to poor structural stability and cycling performance. Herein, a high-entropy layered oxide of Na 0.85 Ni 0.25 Cu 0.12 Ti 0.15 Li 0.08 Ca 0.02 Fe 0.15 Mn 0.31 O 2 (NCFMTLC-1) was prepared by optimizing the ratio of Fe to Mn. It is found that Fe element plays a significant role in the optimization of crystal lattice and the regulation of configurational entropy, improving the cycling and rate performance of materials. In-situ X-ray diffraction combined with DFT calculations reveal that NCFMTLC-1 exhibits superior structural stability with minor reversible phase transition during charge/discharge processes, in stark contrast to its Fe-free counterpart. Therefore, the prepared NCFMTLC-1 cathode demonstrates impressive rate performance (discharge capacity of 96.1 mAh/g at 5C) and cycling stability (83.4% capacity retention after 400 cycles). This work demonstrates that adjusting Fe/Mn ratio is an effective strategy to improve the electrochemical properties of high-entropy materials, offering valuable guidance for the future design of advanced cathode materials for SIBs.