Key Takeaways & Executive Findings
- •• • Increasing mesopore content in porous carbon reduces surface floating silicon by promoting deeper silicon deposition, as evidenced by a high specific capacity of 693.1 mAh/g after 150 cycles at 0.5 C (900 mA/g). • • Excessive surface floating silicon hinders lithium-ion diffusion kinetics and accelerates SEI growth, leading to capacity fading and electrode degradation. • • Porous carbon with higher micropore volume enables higher silicon mass loading but also increases surface silicon formation, necessitating a balance between pore volume and mesoporosity. • • Optimizing pore structure and silane deposition duration can alleviate floating silicon formation, offering a pathway to improve cycling stability of CVD-derived silicon-carbon anodes.
Abstract
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.
1. Introduction
Silicon anodes offer a theoretical capacity of 3579 mAh/g, far exceeding graphite's 372 mAh/g, but suffer from low electronic conductivity and up to 300% volume expansion during lithiation. Chemical vapor deposition (CVD) of silicon onto carbon substrates has emerged as a promising strategy to buffer volume changes and enhance conductivity. However, the deposition process often results in silicon accumulating on the external carbon surface—termed 'floating silicon'—which degrades electrochemical performance. The influence of the carbon carrier's pore structure on this phenomenon remains poorly understood, hindering the rational design of high-performance silicon-carbon anodes.
This study addresses this gap by systematically varying the pore architecture of porous carbon via KOH activation ratios. By correlating pore characteristics with silicon deposition behavior and cycling stability, the authors identify that excessive surface silicon impedes lithium-ion transport and destabilizes the solid electrolyte interphase (SEI). They demonstrate that increasing mesopore content facilitates deeper silicon infiltration, reducing surface silicon and extending cycle life. These findings provide actionable guidelines for optimizing CVD parameters and carbon matrix design, directly tackling the bottleneck of capacity fade in silicon-carbon anodes.
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Yang Fei, Huang Qiang, Yi Zonglin, Ye Lin, Xie Lijing, Chen Jingpeng, Su Fangyuan (2026). Improving the porous carbon matrix to suppress the formation of surface silicon for improved cycling stability. New Carbon Materials. https://doi.org/10.1016/S1872-5805(26)61102-X
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Frequently Asked Questions
What is the specific capacity retention after prolonged cycling, and how does it compare to conventional graphite anodes?
The optimized silicon-carbon composite maintains a specific capacity of 693.1 mAh/g after 150 cycles at 0.5 C (900 mA/g), which is significantly higher than graphite's theoretical capacity of 372 mAh/g, indicating superior energy density potential.
How does the pore structure of the carbon matrix influence the distribution of deposited silicon, and what are the implications for electrode stability?
Increased mesopore content promotes deeper silicon deposition into the pore channels, reducing the formation of surface floating silicon. This minimizes lithium-ion diffusion barriers and SEI instability, thereby enhancing cycling stability.
What are the main degradation mechanisms associated with excessive surface silicon, and how can they be mitigated?
Excessive surface silicon hinders lithium-ion diffusion kinetics, leading to active lithium accumulation, severe electrode expansion, accelerated SEI growth, and active material detachment. Mitigation strategies include optimizing pore structure to reduce surface silicon and employing effective binders to suppress volume expansion.
What is the role of KOH activation ratio in tailoring the pore structure, and how does it affect silicon loading?
Varying the KOH activator ratio adjusts the micropore and mesopore volumes. Higher micropore volume increases silicon mass loading, but also raises surface silicon content. Moderately increasing mesopores in high-microporosity carbon balances loading and reduces surface silicon, improving performance.
Are there any scalability concerns for the CVD process in industrial production of silicon-carbon anodes?
While the study does not directly address scalability, the findings suggest that precise control of pore structure and silane deposition duration is critical. Industrial implementation would require uniform deposition across large batches, which may pose challenges in maintaining consistent pore architecture and silicon distribution.
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