High valence pillar engineering toward near-zero-strain structural reversibility in high entropy layered oxide cathode.

Abstract

O3-type layered oxides are attractive cathode candidates for rechargeable sodium-ion batteries (SIBs) due to their favorable energy density and straightforward synthesis. However, such materials undergo intricate phase transformations and pronounced structural degradation, leading to rapid electrode failure. Herein, a near-zero-strain high-entropy Na0.95Fe0.2Co0.2Ni0.2Mn0.2Ti0.15Sb0.05O2 (denoted as Sb-FCNMT) is designed by introducing high-valence cation dopants. Specifically, the doped Sb5+ shortens the transition metal‑oxygen bond length to form the strong SbO covalent bonds, which effectively anchor the transition metal layers. Detrimental phase transformations and lattice mismatch are suppressed, and near-zero-strain structural reversibility is achieved. Furthermore, Sb doping creates a hydrophobic passivation layer that mitigates air sensitivity, while concurrently expanding the O-Na-O channels to reduce Na+ migration energy barrier and interfacial impedance. Notably, the Sb-FCNMT cathode delivers a high initial capacity of 138.2 mAh g-1 with 88.3% retention after 100 cycles at 0.1C, along with excellent wide-temperature adaptability, outstanding air stability and full cell performance. This high-valence cation doping strategy opens new avenues for designing robust O3-type cathodes toward practical sodium-ion battery applications.