Ultrahigh-Ni layered oxides, LiNixCoyMn1−x−yO2 (x ≥
0.85), have attracted increasing attention as promising cathode materials
for high-energy-density lithium-ion batteries (LIBs). However, structural
instability during the cyclic charge/discharge process limits their
widespread application. Here, we present a bulk and interfacial synergistic
modification strategy that combines trace (∼1%) Nb doping with carbon
coating to improve the electrochemical performances of Li-
Ni0.9Co0.05Mn0.05O2 (NCM90) cathodes. The introduction of Nb doping
stabilizes the crystal structure and accelerates Li+ ion diffusion by
expanding the interslab spacing of the layered channels in NCM90.
Simultaneously, the Ketjen black carbon coating effectively reduces the
interfacial resistance and shields the NCM90 cathodes from harmful
electrolyte corrosion. Our developed dual modification leads to a synergistic effect, unlocking remarkable improvements in both
electrochemical performance and structural stability of NCM90. The optimized Nb-doped NCM90@C delivers exceptional rate
capability (∼121 mAh g−1 at 10 C) and cyclic performance (∼192 mAh g−1 after 100 cycles at 0.5 C). Notably, voltage and capacity
decay during cycling is significantly suppressed, showcasing the powerful impact