A Novel Bifunctional Surface Coating Method to Effectively Eliminate Residual Li on NCM811 by Using Uniformly Dispersed Metal Oxide Solution

A uniformly coating transition metal oxide solution (TS-M) was developed to simultaneously remove residual Li compounds (RLCs) and stabilize the surface of NCM811 material. XRD analysis revealed that the synthesized cathode samples (TS-M, where M = Ti, Ge, Sn) exhibited hexagonal α-NaFeO2 structures without impurity phases. FE-SEM and EDX results confirmed the formation of a uniform metal oxide coating (TS-Ti, TS-Ge: and TS-Sn) on the surface of NCM811, demonstrating its potential as a high-performance cathode material for lithium-ion batteries (LIBs). Among the treated samples, the TS-Sn sample delivered an excellent discharge capacity of 172.4 mAh g−1 with a retention of 90.4% after 50 cycles at a 1.0 C rate, outperforming the TS-Ge and TS-Ti samples. Electrochemical impedance spectroscopy (EIS) further validated the improved impedance of NCM samples after Ti, Ge, and Sn coatings. Based on these findings, the application of Ti, Ge, and Sn metal oxide coatings to NCM811 is considered a reliable surface modification strategy for enhancing electrochemical performance by eliminating RLCs and stabilizing the surface.