High-entropy O3-type cathode enabling low-temperature performance for sodium-ion batteries

High-entropy layered oxide (HEO) cathodes have become a focal point of research in sodium-ion batteries. Herein, we identify two guidelines that are vital for the design and fabrication of HEO O3-type cathodes: enhanced energy storage capacity and robust cathode architecture. To achieve these benchmarks, precise methods are required to adjust the energy levels of the transition metals and maintain ionic radius discrepancies within 15%. We have synthesized and examined various HEO O3-type cathode composites. Specifically, the O3-Na[FeCoNiTi]1/6Mn1/4Zn1/12O2 (O3-FCNTMZ1/12) has demonstrated an impressive reversible capacity of 127.3 mAh g−1, with exceptional long-cycle stability and superb rate capabilities. Notably, the O3-FCNTMZ1/12 cathode exhibits superior Na storage performance at low temperatures. At −20 °C, it maintains 109.6 and 91.1 mAh g−1 at 0.1 and 1 C, respectively, with an impressive 88% capacity retention after 1000 cycles at 1 C. In situ X-ray diffraction analysis reveals a subtle phase transition from O3 to P3, with only a 3% volume expansion. Moreover, ex situ X-ray absorption spectroscopy confirms minimal fluctuation in the TM-O and TM-TM distances, remaining under 9.9%. These well-defined criteria offer a clear strategy for designing and developing the O3-FCNTMZ1/12 cathode, facilitating high-performance sodium-ion batteries, especially for demanding low-temperature applications.