Revealing the Correlation between Coating Content and Li+ Diffusion Kinetics of Nickel-Rich Cathode in Li-Ion Batteries

Coating is a promising strategy for optimizing cathode active materials to enhance the cycle life of nickel-rich cathodes in Li-ion batteries. However, the effects of coating content on Li + diffusion kinetics remain insufficiently understood, limiting the full utilization of the reversible capacity of cathode active materials. In this study, a model system, zirconia-coated LiNi 0.83 Mn 0.05 Co 0.12 O 2 (NMC), is used to investigate the effect of coating content on the Li + diffusion kinetics. We used a wet-coating method to load the surface of the NMC cathode with varying amounts of Zr-O deposits (ZrO 2 and Li 2 ZrO 3 ). Electrochemical performance, including capacity, stability, and rate capability, exhibits a volcano-like trend with respect to coating content. This suggests that while Zr-O coatings can protect cathode particles, excessive coating increases cell internal resistance (IR) and polarization. The combined kinetics analyses using CV, GITT, and EIS reveal that polarization and cathode-electrolyte interphase (CEI) impedance are dependent on coating content, with high coating content impeding Li + diffusion across the interface. These electrochemical insights rationalize the optimization of coating content for NMC cathode materials, i.e., finding optimal balance between surface stability and Li + diffusion kinetics is key to improving the reversibility of the cathode active material. Specifically, for the model system in our study, a 1.5 wt% Zr coating achieves the best overall electrochemical performance.