Lowering Sodium‐Storage Lattice Strains of Layered Oxide Cathodes by Pushing Charge Transfer on Anions

Abstract

Due to a high energy density, layered transition‐metal oxides have gained much attention as the promising sodium‐ion batteries cathodes. However, they readily suffer from multiple phase transitions during the Na extraction process, resulting in large lattice strains which are the origin of cycled‐structure degradations. Here, we demonstrate that the Na‐storage lattice strains of layered oxides can be reduced by pushing charge transfer on anions (O2−). Specifically, the designed O3‐type Ru‐based model compound, which shows an increased charge transfer on anions, displays retarded O3–P3–O1 multiple phase transitions and obviously reduced lattice strains upon cycling as directly revealed by a combination of ex situ X‐ray absorption spectroscopy, in situ X‐ray diffraction and geometric phase analysis. Meanwhile, the stable Na‐storage lattice structure leads to a superior cycling stability with an excellent capacity retention of 84% and ultralow voltage decay of 0.2 mV/cycle after 300 cycles. More broadly, our work highlights an intrinsically structure‐regulation strategy to enable a stable cycling structure of layered oxides meanwhile increasing the materials' redox activity and Na‐diffusion kinetics.