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·h·g–1 at 0.05C), good capacity retention (88.6% after 100 cycles at 0.5C), and excellent rate performance (96.12 mA·h·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.