Application Status of Silicon Anode Materials

Application Status of Silicon Anode Materials

In order to solve the range anxiety problem of electric vehicle users, it is necessary to improve the battery energy density. There are many ways to improve the battery energy density, such as optimizing the battery structure, increasing the energy density of active materials, reducing the proportion of inactive materials, etc. For anode materials, the capacity of graphite anode widely used in commercial lithium batteries is about 360mAh/g, which is very close to its theoretical specific capacity (372mAh/g), so it is difficult to make a breakthrough in graphite anode. Therefore, people turn their attention to silicon material. In lithium batteries, the silicon material forms Li22Si5 at high temperature. The corresponding specific capacity is 4200mAh/g, and Li15Si4 is formed at room temperature, and the corresponding specific capacity is 3579mAh/g, and the delithium potential of silicon is relatively low, so silicon as a negative electrode can reduce the material consumption, improve the energy density of the battery, is the next important development direction of the negative material of power battery.

Silicon Carbon Anode Material

Silicon, as a cathode material, will produce a large volume change, and the continuous shrinkage and expansion with charge and discharge will cause the material powder, affecting the cycle life of the battery. At present, the commercial silicon material negative is generally silicon carbon composite system, there are two kinds of silicon - carbon negative and silicon oxide-carbon negative. In contrast, silicon oxide-carbon negative has smaller volume expansion and better rate performance than silicon - carbon negative, but the capacity and first cycle coulomb efficiency is lower

Silicon carbon composite system, the carbon can improve the electrical conductivity of the material, the buffer volume change of silicon, avoid the reunion of silica particles, such as the structure of silicon carbide material carries on the reasonable design can better inhibit the volume change of materials, such as silicon carbon materials can be designed as core - shell structure, porous structure, etc., for the volume expansion reserved seat or buffer space.

In addition, there is another problem of silicon carbon anode that attracts attention. As SEI film on the surface of silicon anode material consumes a large amount of lithium source and reduces the first effect of battery, prelithium is usually used to solve this problem. For example, the introduction of lithium foil, lithium powder, pre-lithium additives and other physical, chemical or electrochemical means to supplement the lithium source required for the formation of SEI film in advance can effectively improve the first effect of battery.

To sum up, the silicon carbon anode has high capacity, but its lifespan is slightly lower due to volume expansion and other issues. Therefore, it is usually matched with a high-nickel NCM cathode with the same low cycle life but high specific capacity, and the first effect is improved by means of lithium supplementation to maximize the Improve battery energy density.