Regulating Surface Chemistry and Interfacial Kinetics of Ni-Rich NCM Cathodes via a Polyaniline-Derived Interphase.

Ni-rich LiNixCoyMn1-x-yO2 cathodes (NCM, Ni ≥ 80%) are promising for high-energy lithium-ion batteries, but their practical use is constrained by surface instability, interfacial side reactions, and sluggish charge-transfer kinetics during cycling. Herein, a conductive interphase derived from polyaniline (PANI) was constructed on LiNi0.9Co0.05Mn0.05O2 (NCM90) through a facile solution-assisted coating strategy. The optimized NCM90@PANI preserves the layered structure and particle morphology of NCM90 while forming a thin and continuous PANI-containing surface layer. Benefiting from this interfacial modification, NCM90@PANI exhibits enhanced cycling stability, improved rate capability, and better air-storage stability than pristine NCM90. The improvement is attributed to the protective and kinetically favorable interphase, which reduces interfacial polarization, maintains favorable Li+ transport kinetics, suppresses continuous electrolyte decomposition, and mitigates the accumulation of resistive surface byproducts. The PANI-containing interphase also reduces H2O/CO2-induced surface degradation during air storage. Diffusion-stress simulation further qualitatively illustrates that improved interfacial flux uniformity can promote a more homogeneous Li distribution and alleviate localized stress concentration. This work demonstrates that PANI-derived interphase engineering provides an effective strategy for simultaneously regulating the surface chemistry and interfacial kinetics of Ni-rich NCM cathodes.