Composition-Dependent Electrochemical Performance of Pitch-Derived Carbon-Enhanced Silicon–Graphite Composite Anodes for Lithium-ion Batteries

Abstract

Silicon–graphite composite anodes are high-potential contenders for high-energy lithium-ion batteries, yet their practical application is hindered by the volume expansion of silicon during cycling. In this work, silicon–graphite–pitch composite anodes containing 10–15 wt% micron-sized silicon and 20–25 wt% coal tar pitch is prepared through solution-assisted mixing followed by carbonization. The structural and morphological characterization indicates the coexistence of silicon, graphite and pitch-derived carbon within the composite framework. Electrochemical evaluation demonstrates significantly higher reversible capacities than graphite, delivering initial capacities of ~558 mAh g⁻¹, ~796 mAh g⁻¹ and ~809 mAh g⁻¹ for the samples containing 10%, 12% and 15% silicon, respectively. After 100 cycles at 0.2 mA cm⁻2, the corresponding capacity retentions are 87.44%, 72.03%, and 68.35%. Quantitative irreversible capacity analysis reveals composition-dependent differences in capacity loss, with greater irreversible capacity accumulation in silicon-rich composites. Furthermore, the composite anode containing 12% silicon, when tested in an NMC-811 full-cell configuration, delivers an initial discharge areal capacity of ~2.5 mAh cm⁻² and sustains electrochemical activity over 100 cycles. The study highlights the role of composition on the electrochemical response of silicon–graphite–pitch composites and offers guidance for the design of silicon-based composite anodes for lithium-ion batteries.