Revealing the Capacity Oscillation Mechanism of Chemical Vapor Deposition-Derived Silicon–Carbon Anodes at Different Cycling Stages: The Effect of Trapped Active Lithium

Silicon-carbon composite materials prepared by chemical vapor deposition (CVD) have become one of the most promising anode materials for next-generation lithium-ion batteries. However, the capacity oscillation mechanism of silicon-carbon composite anodes in half-cells under the constant-current charge-discharge protocol remains poorly understood, hindering their performance assessment and practical application. In this work, we quantify the trapped active lithium due to kinetic limitations after different numbers of cycles by using a constant current-constant voltage (CC-CV) protocol. Subsequently, we characterize the electrochemical performance and solid electrolyte interphase (SEI) layer of the silicon-carbon composite anodes at different cycling stages through differential capacity curve (dQ/dV) analysis, electrochemical impedance microscopy (EIS), galvanostatic intermittent titration technique (GITT), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). We find that polarization is the main influencing factor governing abnormal capacity variation. During the first cycling stage, a low content of trapped active lithium impedes lithium-ion diffusion at low potential, while continuous SEI growth induces a significant polarization increase. In contrast, moderate trapped active lithium and stable SEI during the second stage enhance diffusion kinetics and reduce overall polarization. This work provides deeper insights for the development and evaluation of silicon-carbon composite anodes in half-cells.