Capacitor carbon and porous carbon for silicon carbon are two similar materials, both of which belong to porous carbon, but they differ in electrochemical properties, production methods and application fields. The characteristics of these two materials and the differences between them will be introduced below.
Capacitor Carbon
Capacitor carbon is a high-surface-area, porous, activated carbon. It is widely used as an electrode in energy storage devices. Capacitor carbon production usually involves carbonizing raw materials, like coal and coconut shell. It then undergoes an activation process. The activation process can be physical (using water vapor or carbon dioxide) or chemical (using acid, base or salt). Capacitor carbon has three main advantages. It is low-cost, has a large surface area, and a rich pore structure. These traits give it a high charge storage capacity as an electrode material in supercapacitors.
The main features of capacitor carbon include:
Large specific surface area: capacitor carbon has an extremely large specific surface area, which enables it to adsorb a large amount of electrolyte solution, thereby forming a double layer on the electrode surface, which is the key to store charge.
Well-developed pore structure: capacitor carbon has a well-developed microporous and mesoporous pore structure, which is conducive to the wetting of the electrolyte and the rapid movement of ions, thereby improving the performance of the capacitor.
High conductivity: the high ionic conductivity of capacitor carbon facilitates rapid charging and discharging, which is an important factor in achieving high power density of super capacitors.
High chemical stability: in various acidic and alkaline electrolytes, capacitor carbon exhibits high chemical stability, ensuring the stable performance of the capacitor in different environment.
Environmentally friendly: capacitor carbon does not contain heavy metals and will not pollute the environment. It is an environmentally friendly energy storage material.
Porous Carbon for Silicon Carbon
Porous carbon for silicon-carbon is a key material upstream of silicon-carbon negative electrode, it plays an important role in improving battery performance.
The main features of porous carbon for silicon carbon include:
Porous carbon has a good pore structure and a large surface area. This can provide a suitable structure for nano-silicon deposition. It also allows space for silicon to expand during charging. This improves the performance of lithium-ion batteries. A large pore volume means more active sites. This increases the battery’s energy storage capacity. Excessive pore volume will reduce strength. So, it must be controlled within a reasonable range.
Conductivity: porous carbon material has high conductivity, which is essential for the rapid charging and discharging of the battery. High conductivity can reduce the internal resistance of the battery and improve the overall energy conversion efficiency.
Impurity content and carbon skeleton strength: high-quality porous carbon material has low impurity content and high carbon skeleton strength, which improving the stability and lengthening the service life of the battery during recycling.
Particle size distribution and compaction density: suitable particle size distribution and high compaction density make the porous carbon material easy to handle during battery manufacturing and can improve the energy density of the battery.
The difference between capacitor carbon and porous carbon used in and silicon carbon
Capacitor carbon and porous carbon used to produce silicon carbon are different in properties and usage, which makes capacitor carbon unsuitable for direct applied in the production of silicon carbon negative electrode material. Here are some key differences and reasons:
Capacitor carbon has a very developed microporous structure. This makes it a great electrode material for supercapacitors. The micro pores provide a large surface area to adsorb ions in the electrolyte and store charge. However, silicon-carbon negative electrodes need a larger pore structure. It must accommodate the expansion of silicon particles. This stops the material from breaking or falling off due to volume changes during charging and discharging.
Mechanical strength and stability: silicon-carbon negative electrode material will undergo significant volume changes during the charge and discharge process, which requires the base material to have sufficient mechanical strength and stability to bear this stress. Although capacitor carbon has good electrochemical properties, its mechanical strength and structural stability may not be sufficient to cope with the volume changes of silicon particles, thereby affecting the cycle life of the battery.
Thermal stability: in the process of producing silicon-carbon negative electrode material, high temperature treatment steps may be required. The thermal stability of capacitor carbon may not be sufficient to bear high temperature condition, which may cause damage of structure or decrease of performance.
Conductivity: although capacitor carbon has a certain conductivity, silicon-carbon negative electrode material usually requires higher conductivity to ensure rapid electron transmission. Therefore, additional conductive agents or optimized carbon material may be required to improve the overall conductivity.
Silicon dispersion: in silicon-carbon anode material, silicon particles need to be evenly dispersed in the carbon matrix to maximize the high capacity of silicon. The pore structure of capacitor carbon may not be conducive to the uniform dispersion and fixation of silicon particles.
Although capacitor carbon performs well in supercapacitors, its specific pore structure, mechanical strength, thermal stability and conductivity are not suitable for direct use in the production of silicon-carbon ergative electrode material.
How to transform
The transformation of capacitor carbon into porous carbon suitable for silicon-carbon materials requires a series of modification steps to adjust its pore structure, mechanical properties and chemical stability to meet the specific requirement of silicon-carbon composite material.
Here are some possible transformation strategies:
Adjust the pore size : capacitor carbon usually has more micro pores. To adapt to silicon carbon material, it may be necessary to expand the pore size. This would create a mesoporous or macroporous structure. Chemical or physical methods could achieve this. For example, chemical activation (using KOH or NaOH) or physical activation (using water vapor or CO2) can adjust the pore size. This increases the proportion of mesopores and macropores.
Improve mechanical properties. Capacitor carbon may not withstand silicon particle volume changes during charging and discharging.
Its strength can be improved by:
Modifying the carbonization precursor.
Controlling the carbonization temperature.
Adding reinforcing agents, like carbon nanotubes and graphene.
Improve thermal stability: improve the thermal stability of capacitor carbon by high temperature treatment or doping with other elements (such as nitrogen and boron) to ensure that the structural integrity is maintained during the production and application of silicon-carbon composite material.
Improve conductivity: the conductivity of capacitor carbon may not be sufficient to meet the requirement of silicon-carbon composite material. The conductivity can be improved by doping carbon material with better conductivity (such as graphene and carbon black) or coating the surface with a conductive layer.
Modify the surface: modify the surface of the capacitor carbon, to improve its compatibility and adhesion with silicon particles. For example, we can improve the adhesion of silicon particles on the carbon surface. We can do this by oxidizing the surface and using a silane coupling agent. The transformation process must balance cost, efficiency, and performance. In practice, experiments may find the best method and conditions for modification. Also, we must rigorously test the transformed materials. Their performance in silicon-carbon negative electrode material must meet the requirements.