The impact of defective carbon interface engineering on the lithiation behavior of silicon-graphite composite electrodes

In silicon-graphite composite electrodes, the disparity in lithiation potentials between the two components exacerbates the polarization of individual components during charge/discharge processes, consequently diminishing the rate performance of the electrode materials. A robust silicon-defective carbon-graphite interface was created by coating graphite with oxidized pitch and employing surface-bonding techniques, significantly improving the rate performance and overall homogeneity of the electrode materials. The synthesized sample Si@C-MCMB exhibited the specific capacity of around 1617mAh/g at 0.1 A/g with the capacity retention of more than 85 %. In-situ XRD tests and DFT calculations reveal that due to the lower lithiation potential of graphite, it experiences a delayed discharge process within the composite anode, causing silicon to discharge independently during the initial stages of lithiation. However, the broad voltage window of defective carbon could compensate for the independent discharge behavior of silicon, promoting the homogeneity of the electrode. The faster lithium-ion diffusion in defective carbons with small graphite microcrystals and abundant defect sites also enhances the overall rate performance of the electrode materials. The study highlights using defective carbon to enhance Si-graphite composite electrodes for better battery performance, suggesting future research on optimizing the silicon-carbon interface and other carbon-based materials.