High-Entropy Engineering Regulates Na-Ion Transport and Phase Evolution in O3-Type Layered Oxide Cathode

Abstract

Layered oxides have emerged as one of the most promising cathode materials for sodium-ion batteries owing to their high capacities and energy densities. However, they undergo multiple phase transformations during cycling, leading to structural instability and performance degradation. High-entropy design has recently been recognized as an effective strategy to mitigate such instability in O3-type layered oxide cathodes. In this work, an O3-type NaMn0.35Fe0.15Ni0.25Cu0.10Al0.15O2 cathode, with a configurational entropy of ≈1.51 R (at transition metal site), is reported with an expanded Na-layer spacing of 3.3170 Å, enabling facile Na+ transport. Operando Synchrotron X-ray diffraction confirms suppressed monoclinic distortions, preserving the hexagonal framework during cycling. As a result, the cathode delivers a specific discharge capacity of 168.3 mAh g−1 at 0.1C and 122.6 mAh g−1 at 1C, retaining 83.7% after 250 cycles at 1C. Full cells with hard carbon deliver 108.1 mAh g−1 at 0.1C, highlighting the practical applicability of the material. © 2026 Wiley-VCH GmbH.