<p>High-nickel ternary silicon-carbon lithium-ion batteries, which use silicon-carbon materials as anodes and high-nickel ternary materials as cathodes, have already been commercialized as power batteries. The increasing demand for high-energy density and rapid charging characteristics has heightened the urgency of improving their fast charging cycle performance while establishing degradation mechanisms. Based on a pouch battery design with an energy density of 285 Wh·kg⁻¹, this work studied 3 Ah pouch batteries for fast charging cycles ranging from 0.5C to 3C. Non-destructive techniques, such as differential voltage, incremental capacity analysis, and electrochemical impedance spectroscopy, were employed to investigate the effects of charging rates on battery cycling performance and to establish the degradation mechanisms. The experimental results indicated that capacity diving was observed at all charging rates. However, at lower rates (0.5C–2C), more cycles were achieved, while at higher rates (2C–3C), the cycle life remained relatively stable. Computed tomography, electrochemical performance analysis, and physicochemical characterizations were obtained, using scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectrometry. The mechanisms of capacity decrease during 3C fast charging cycles were investigated. It is proposed that the primary causes of capacity diving during 3C fast charging are the degradation of SiO_<i>x</i>, anode polarization, and the simultaneous dissolution of metal ions in the cathode which were deposited at the anode, resulting the continuous growth and remodeling of the SEI membrane at the anode, thereby promoting more serious side reactions.</p> Graphical abstract <p></p>