Enhanced Electrochemical Performance and Cycling Stability of High-Nickel NCM90 Cathodes via g-C3N4 Surface Coating

초록

High-nickel layered oxide cathodes, such as LiNi0.9Co0.05Mn0.05O2 (NCM90), represent promising options for next-generation lithium-ion batteries owing to their high specific capacity and reduced cobalt content. Nevertheless, structural degradation, transition metal (TM) dissolution, and electrolyte decomposition at elevated voltages (>4.1 V vs Li/Li+) significantly constrain their long-term performance. In this investigation, we apply a graphitic carbon nitride (g-C3N4) coating on NCM90 particles through a straightforward two-step thermal annealing process, with melamine as the precursor. The nitrogen-rich g-C3N4 layer enhances the surface structural stability of NCM90, thereby mitigating transition metal (TM) dissolution and facilitating the formation of a stable cathode-electrolyte interphase. Electrochemical impedance spectroscopy revealed a decrease in charge transfer resistance (R-ct) from 220.2 Omega to 144.3 Omega. Following 100 charge-discharge cycles at 0.5C, the g-C3N4-coated NCM90 retained a specific capacity of 179.67 mAh g(- 1) (corresponding to 81% retention), compared to 74.32 mAh g(- 1) (34%) for the pristine sample. Furthermore, the coated sample demonstrated enhanced high-rate performance, with 182.96 mAh g(- 1) at 5C. Notably, in full-cell evaluations for practical cycle life, the g-C3N4-coated NCM90 retained a discharge capacity of 120.16 mAh g(- 1) (83% retention) after 100 cycles at 2C, whereas the pristine sample exhibited only 83.51 mAh g(- 1) (57%). These findings illustrate that g-C3N4 surface coatings effectively alleviate interfacial degradation and enhance electrochemical performance, providing a scalable approach for stabilizing high-voltage Ni-rich cathodes.

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