Silicon-based anodes have a theoretical specific capacity of 4200 mAh/g. This far exceeds the traditional graphite anode’s 372 mAh/g. It has become a key direction for breaking the performance bottleneck of conventional anodes. Chemical vapor deposition (CVD) technology allows uniform silicon deposition on carbon substrates. It also creates a stable silicon-carbon interface. This process has become the core route for commercializing silicon-carbon anodes. In this process, porous carbon materials are not just “carriers.” They are the “core scaffold” that determines the performance limit of CVD silicon-carbon anodes. Their performance directly affects the electrochemical performance and commercialization feasibility of the composite material.
Basic Understanding of Porous Carbon
Porous carbon is a carbon-based material with interconnected pores. According to IUPAC standards, pores are classified as micropores (<2 nm), mesopores (2-50 nm), and macropores (>50 nm). The structural characteristics of different pore sizes determine their functions in CVD silicon-carbon anodes.
Porous carbon also has low electrical resistance. It is resistant to high temperatures, acids, and bases. It can build a stable conductive network, ensuring electrode cycle life. The pore ratio and porosity can be adjusted during the process to meet various CVD silicon-carbon anode performance requirements.
Core Role and Advantages of Porous Carbon in CVD Silicon-Carbon Anodes
Currently, the industrialization of CVD silicon-carbon anodes faces two major challenges:
Silicon volume expansion during lithium insertion causes electrode pulverization and active material shedding.
Side reactions between silicon and electrolyte generate thick SEI layers, reducing the battery’s first-cycle efficiency and cycle life.
Porous carbon offers solutions to these two problems:
Buffering silicon’s volume expansion:
The multi-level pore structure in porous carbon forms a “three-tier buffer system.” These pores provide physical space for silicon to expand. They also disperse stress through elastic deformation, reducing the risk of particle fracture. Mesopores match silicon particle sizes. After lithium insertion, silicon expands and fills these pores, preventing mutual compression between particles.
Isolating silicon from the electrolyte and stabilizing the SEI layer:
On one hand, the carbon skeleton of porous carbon wraps around silicon nanoparticles. This reduces direct contact between silicon and the electrolyte. CVD also involves secondary carbon coating. This forms a dense carbon layer on the surface of the porous carbon/silicon composite material. The dual isolation reduces side reactions by more than 60%. On the other hand, reduced side reactions prevent SEI layers from forming and shedding due to silicon particle fracture. This improves energy conversion efficiency and cycle life.
Preparation Methods for Porous Carbon
Activation Method
The activation method involves mixing carbon precursors with activating agents and performing pore-forming reactions under high-temperature inert gas conditions. This method includes physical activation and chemical activation.
(1) Physical activation:
Biomass or coal-based materials like coconut shells or anthracite are used as precursors. After crushing and impurity removal, the material is carbonized at high temperatures to form an initial carbon skeleton. CO₂ or steam is then introduced as an activating agent at 800-1100°C to etch the carbon skeleton and create pores. After cooling and screening, the product is ready. This method is environmentally friendly, with no chemical reagent residues, low-cost, and suitable for mid-to-low-end porous carbon production. However, the mesopore content is generally limited to below 50%, which may not meet high-silicon-load requirements.
(2) Chemical activation:
High-carbon materials, like phenolic resin or anthracite, are used as precursors. The precursor is mixed with an activating agent in a 3:1 ratio. It is then heated for carbonization and activation. After the reaction, the activating agent is washed away, and the material is dried. Porous carbon made using chemical activation has higher mesopore content, stronger pore structure control, and a surface area of up to 2500-3000 m²/g.
Metode Template
In the template method, carbon precursors are filled into templates and heated at high temperatures. The precursor gradually carbonizes, and the template is then removed to obtain porous carbon. The method is divided into hard template and soft template methods.
(1) Hard template method:
Materials such as alumina or molecular sieves with fixed pore structures are used as templates. The precursor is impregnated into the template pores. After carbonization at 800-1000°C, the template is dissolved using acid to obtain porous carbon with complementary pore structures. This method achieves mesopore order greater than 90% and pore size deviation <5%. It ensures uniform deposition of silicon, but the cost of templates is high, and the process is complex. It is used for lab research or small-scale high-end production.
(2) Soft template method:
Block copolymers or surfactants are used as templates. They self-assemble into mesoporous micelles when mixed with carbon precursors like sucrose or phenolic resin. The mixture is then carbonized at 600-800°C. This method results in mesopores comprising 60-70% of the structure, with a lower cost than the hard template method.
Metode Sol-Gel
The sol-gel method involves mixing alcohol salts or metal inorganic salts with solvents to form a solution, which undergoes hydrolysis and condensation to form a sol-gel. After aging, drying, and low-temperature sintering, porous carbon is produced. In sol-gel synthesis, pore collapse can occur during the drying stage. To avoid this, the template method is often used in combination with the sol-gel method.
Bubuk Epik
Epic Powder has over 20 years of experience in powder processing. We offer integrated solutions ranging from crushing, grinding, klasifikasi to modifikasi. By optimizing the preparation of porous carbon materials, we ensure enhanced performance and long-term cycling for CVD silicon-carbon anodes, contributing to the commercialization of high-performance lithium-ion batteries.
