Key Takeaways & Executive Findings
- •• • The Si/C composite achieves a specific capacity of 2179 mAh g–1 with an initial Coulombic efficiency (ICE) of 93.5% and a low specific surface area of 1.32 m2 g–1, enabling high energy density and reduced side reactions in full cells. • • A carbon framework with micropores of ~1.9 nm confines amorphous silicon, limiting volume expansion to 35.8% from delithiated to lithiated state, which is critical for electrode integrity and long-term cycling. • • Optimizing the median particle size (D50) to 8.2 μm yields a rate retention of 97.0% at 3 C relative to 0.1 C, demonstrating balanced ionic/electronic transport and mechanical robustness. • • In a practical 879 mAh pouch cell (graphite hybrid anode paired with NCM523), the material retains 87.46% capacity after 1000 cycles at 1 C, with a battery expansion rate below 8%, proving industrial viability.
Abstract
Silicon-carbon (Si/C) composites are promising high-capacity anode materials for next-generation lithium-ion batteries, but their commercialization is hindered by severe volume expansion during cycling. We report a chemical vapor deposition method using the pyrolysis of silane, in which ultrafine nano-Si enters a porous carbon framework to produce kilogram-scale Si/C composites. The carbon framework with abundant micropores (~1.9 nm) confines the amorphous silicon and accommodates the volume changes of nano-Si during both lithiation and de-lithiation. The resulting Si/C composites have a 56.76% Si content and have a specific capacity of 2179 mAh g–1, a high initial Coulombic efficiency (ICE) of 93.5%, and a low specific surface area (1.32 m2 g–1). In addition to the nanoconfinement effect, the median particle size (D50, 7.3-13.0 μm) of the carbon framework was shown to control the mechanical strength, coating uniformity and Li+ transport. A D50 of 8.2 μm endows the Si/C composites with outstanding comprehensive properties. They have an excellent rate performance with a 97.0% retention at 3 C relative to 0.1 C, show only minor variations in ICE difference at 60 ℃/-20 ℃ compared with room temperature, and have a low expansion of 35.8% from the delithiated to the lithiated state. The composite was then mixed with graphite to prepare the anode, which was then paired with an NCM523 cathode to assemble pouch cells. The pouch cell retained 87.46% of its initial capacity after 1000 cycles at 1 C. Because of the low expansion of the electrode, the material avoids structural degradation during cycling and thus has an excellent long-term stability.
1. Introduction
Silicon anodes offer a theoretical capacity of 3579 mAh g−1, nearly ten times that of graphite (372 mAh g−1), but their commercialization is stalled by two critical bottlenecks: a ~300% volume change during lithiation, which causes particle pulverization and electrode degradation, and intrinsically low electronic conductivity (~10−3 S cm−1) and sluggish lithium-ion diffusion (~10−12 cm2 s−1), which limit rate capability. Conventional mitigation strategies, such as nanostructuring or carbon coating, often sacrifice volumetric energy density or introduce complex, costly processing steps, failing to meet industrial scalability and cost targets.
This work addresses these bottlenecks by employing a scalable chemical vapor deposition (CVD) method using silane pyrolysis to infiltrate ultrafine nano-Si into a resin-based porous carbon framework with abundant micropores (~1.9 nm). The nanoconfinement effect accommodates volume changes, while micron-scale optimization of the carbon framework (D50 control) enhances mechanical strength and Li+ transport. The resulting Si/C composite achieves a high silicon content (56.76%), ultra-high capacity (2179 mAh g−1), high ICE (93.5%), and low expansion (35.8%), enabling stable cycling in practical pouch cells. This synergistic design offers a mass-producible route for next-generation high-energy-density anodes.
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Ye Lin, Huang Qiang, Peng Gongchang, Tian Guilei, Bai Hongyou, Zhou Xiaoqing, Wang Junkuo (2026). Changing the carbon framework to produce low-expansion silicon-carbon composites for high-performance lithium-ion batteries. New Carbon Materials. https://doi.org/10.1016/S1872-5805(26)61109-2
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Frequently Asked Questions
What is the failure mechanism of Si/C anodes under repeated cycling, and how does the micropore confinement (~1.9 nm) mitigate it?
Silicon undergoes ~300% volume expansion during lithiation, causing particle fracture and loss of electrical contact. The micropores (~1.9 nm) confine amorphous silicon, limiting expansion to 35.8% from delithiated to lithiated state, preserving electrode integrity and achieving 87.46% capacity retention after 1000 cycles at 1 C.
How does the median particle size (D50) of the carbon framework affect electrochemical performance, and what is the optimal value?
D50 controls mechanical strength, coating uniformity, and Li+ transport. A D50 of 8.2 μm provides balanced properties, yielding a rate retention of 97.0% at 3 C relative to 0.1 C and stable cycling. Larger or smaller D50 values compromise either mechanical integrity or ionic transport.
What is the cost and scalability of the silane-based CVD process for kilogram-scale production?
The process is demonstrated at kilogram scale, indicating industrial viability. Silane pyrolysis is a well-established method, but cost depends on silane price and deposition efficiency. The high silicon content (56.76%) and low surface area (1.32 m2 g−1) reduce electrolyte decomposition, potentially lowering overall cell cost.
How does the Si/C composite perform under extreme temperatures, and what is the impact on initial Coulombic efficiency (ICE)?
The composite shows minor variations in ICE difference at 60 °C and -20 °C compared to room temperature, indicating robust thermal stability. This is crucial for automotive applications where temperature fluctuations are common.
What is the electrode expansion rate in a full cell, and how does it affect long-term durability?
The battery expansion rate after 1000 cycles is below 8%, demonstrating low electrode swelling. This prevents structural degradation and contact loss, contributing to the high capacity retention of 87.46% at 1 C.
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