The carbonaceous anode material exhibits minimal volume change during charge and discharge, offering excellent cycle stability and being a mixed conductor of both ions and electrons. Additionally, silicon and carbon share similar chemical properties, allowing them to bond tightly together. As a result, carbon is often used as the preferred substrate for combining with silicon.
In Si/C composite systems, silicon particles serve as active materials that provide lithium storage capacity. Carbon acts as a buffer, mitigating the volume expansion of silicon during charge and discharge, enhancing the conductivity of the silicon material, and preventing particle agglomeration. Thus, Si/C composites combine the advantages of both components, offering high specific capacity and long cycle life, making them promising candidates to replace graphite as next-generation anode materials for lithium-ion batteries.
From a structural perspective, current Si/C composites can be classified into cladding and embedded structures. In the cladding structure, a carbon layer is coated on the surface of silicon particles to reduce the volume effect and improve conductivity. Based on the coating structure and silicon particle morphology, these coatings can further be categorized into core-shell, egg-yolk-shell, and porous types.
Porous structures are particularly effective in managing the volume changes of silicon during lithiation/delithiation. Porous silicon is typically fabricated using template methods, where internal voids provide space for expansion, reducing mechanical stress. The resulting Si/C composites exhibit enhanced structural stability during cycling.
Research has shown that in porous Si/C composites, a uniform pore distribution around silicon particles creates fast ion transport channels, while a large surface area increases reactivity, leading to excellent rate performance. This makes such materials highly suitable for fast-charging applications.
Li et al. synthesized a 3D-connected porous Si/C composite via controlled reduction of silica aerogel. After 200 cycles at 200 mA/g, the material retained a capacity of 1552 mA·h/g, and even at 2000 mA/g, it maintained 1057 mA·h/g after 50 cycles.
Bang et al. created a 3D porous silicon structure by depositing silver nanoparticles on silicon powder through galvanic displacement, followed by etching and carbon coating via acetylene pyrolysis. The composite showed an initial capacity of 2390 mA·h/g at 0.1 C and a Coulomb efficiency of 94.4%. At a 5C rate, it retained 92% of its low-rate capacity, demonstrating outstanding rate capability.
Moreover, after 50 cycles, the electrode thickness increased by only 39%, and the volume-specific capacity reached 2830 mA·h/cm³, five times that of commercial graphite.
Yi et al. prepared porous silicon by etching SiO₂ at 950°C, then coated it with carbon via acetylene pyrolysis. The material retained 1459 mA·h/g after 200 cycles at 1 A/g, and even at 12.8 A/g, it maintained 700 mA·h/g. It also exhibited a high tap density and volume-specific capacity of 1326 mA·h/cm³ after 50 cycles at 400 mA/g.
Further studies found that optimizing the primary particle size of silicon improved performance, with the best results observed at 15 nm, achieving 1800 mA·h/g after 100 cycles. Smaller particles lead to less volume change and more stable SEI formation.
Optimizing carbonization temperature and time also enhanced performance. At 800°C and 20% carbon loading, the material retained 1200 mA·h/g after 600 cycles with nearly no capacity loss and a Coulomb efficiency of 99.5%.
Porous Si/C composites are cost-effective and scalable for industrial production.
Recently, Lu et al. developed a novel structure called nC–pSiMPs, where porous micro-silicon (pSiMPs) was coated with carbon only on the outer surface, leaving the inner silicon nanoparticle free of carbon. This design allows the pores to accommodate volume expansion without cracking the carbon shell, ensuring structural stability.
In this structure, the carbon layer prevents electrolyte penetration, reduces contact between silicon and electrolyte, and facilitates the formation of a stable SEI film on the carbon coating. In contrast, when inner silicon is also coated with carbon, the larger contact area and potential rupture of the carbon layer can lead to thicker SEI films and reduced performance.
As a result, the nC-pSiMPs electrode showed superior cycle stability, retaining 1500 mA·h/g after 1000 cycles at 1/4 C. After 100 cycles, the electrode thickness increased by only 7%, and the volume-specific capacity reached 1003 mA·h/cm³, significantly higher than that of commercial graphite.
High Power Led Driver
In situations which require the use of high powered LEDs and/or a greater number of LEDs in series, a high power LED driver is an appropriate addition to the circuit. Care must be used not to overpower the circuit, as this can result in a number of burnt out lights. Applications which commonly require the use of a high power LED driver include:
- Automotive applications such as exterior LED lights (brake lights, tail lights, etc), display panel usage, interior vehicle lights, etc.
- Hotels, stores, restaurants, bars and more where a particular mood is desirable.
- Emergency lights, flashlights, landscape lighting, underwater lighting, lanterns and more.
- LED lights used in indoor plant growth facilities.
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