Improving the porous carbon matrix to suppress the formation of surface silicon for improved cycling stability
Silicon-carbon composites prepared by chemical vapor deposition (CVD) are promising anode materials for high-energy-density lithium-ion batteries. However, the influence of the pore structure of the porous carbon (PC) carrier on silicon deposition behavior, and the impact of surface silicon on cycling stability, remain unclear. This study systematically investigates these effects using nitrogen adsorption-desorption analysis, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Porous carbons with varying pore architectures were synthesized by adjusting KOH activator ratios. Results show that increased micropore volume facilitates higher silicon mass loading, but also elevates the content of surface floating silicon due to greater silane exposure. Moderately increasing mesopores in high-microporosity carbon promotes deeper silicon deposition, reducing surface floating silicon. Excessive surface floating silicon hinders lithium-ion diffusion kinetics, leading to accumulation of active lithium, accelerated SEI growth, and electrode degradation. Electrochemical testing reveals that the optimized silicon-carbon composite maintains a high specific capacity of 693.1 mAh/g after 150 cycles at 0.5 C (900 mA/g). This work provides new insights into the development and failure mechanisms of CVD-derived silicon-carbon composite anodes, emphasizing the critical role of pore structure in mitigating surface silicon and enhancing cycling stability.