A Universal Strategy toward Air‐Stable and High‐Rate O3 Layered Oxide Cathodes for Na‐Ion Batteries

As one of the fascinating high capacity cathodes, O3-type layered oxides usually suffer from their intrinsic air sensitivity and sluggish kinetics originating from the spontaneous lattice Na extraction during air exposure and high tetrahedral site energy of Na+ diffusion transition state. What is worse, the improvement on the two handicaps is hard to simultaneously realize because of the contradiction between Na containment suggested in air stability mechanism and enhanced Na diffusion mentioned in kinetics strategy. Herein, it is shown that a simple strategy of introducing proper Na vacancies into lattice can simultaneously realize a dual performance improvement. Na vacancies decrease the charge density on transitional metal ions and enhance the antioxidative capability of material, ensuring a stable lattice Na containment for Na0.93Li0.12Ni0.25Fe0.15Mn0.48O2 when exposed to air. Additionally, more Na+ diffusional sites and enlarged Na layer spacing are obtained and result in a significantly decreased energy barrier from approximate to 1000 to 300 meV and a high rate capability of 70.8% retention at 2000 mA g(-1). Remarkably, such a strategy can be easily realized by either pre- or post-treating, which exhibits excellent universality for various O3 materials, implying its enormous potential to promote the commercial application of O3-type cathodes.