Regulating Interfacial Compositions to Build a Stable Superlattice Structure of Layered Oxide Cathode Materials for Sodium-Ion Batteries

The introduction of a superlattice structure in layered oxides for sodium-ion batteries (SIBs) is an effective strategy for improving structural stability. However, carbonate impurities adhering to the surface of layered oxides increase the side reactions and block the Na+ transport channels. The deteriorating interfacial environment leads to the gradual disappearance of the superlattice structure during cycling, which affects the structural stability of SIBs. Herein, a stable superlattice structure is successfully achieved by reasonable interfacial regulation to remove carbonate impurities adhering to the surface of P2-Na0.80Li0.13Ni0.20Mn0.67O2. The residual impurities, such as Na2CO3 and NaHCO3, on the surface of the layered oxides react with Si4+ to generate about 5 nm of a Na2SiO3 coating layer, which can improve the air stability of the cathode materials. Meanwhile, the introduction of Si into the bulk phase significantly enhances the length of the c-axis, resulting in faster Na+ diffusion kinetics. The cyclic voltammetry (CV) and ex situ X-ray photoelectron spectroscopy (XPS) results show that the reversible redox of the lattice oxygen is activated by interfacial regulation. Thus, LNM-2% NSO exhibits a high reversible specific capacity (170.95 mA<middle dot>h<middle dot>g(-1) at 0.05C), good capacity retention (88.6% after 100 cycles at 0.5C), and excellent rate performance (96.12 mA<middle dot>h<middle dot>g(-1) at 5C) in a wide voltage range of 1.5-4.5 V. This study confirms the feasibility of regulating the interfacial composition to achieve a stable superlattice structure, which has implications for the design of cathode materials with excellent air stability.