The theoretical specific capacity of Si is as high as 4200mAh/g, which is 10 times higher than the theoretical specific capacity of graphite; the lithium intercalation potential of Si is low, which is 0.37mV Li/Li+; and Si is the second most abundant element on the earth, which is not harmful to the environment. Destruction will occur, and the production process of nano-silicon is mature and low-cost, so Si is regarded by researchers as the main anode material to replace graphite in the future.

However, in the process of lithium intercalation and extraction, the volume of Si will expand and contract, and the change rate can reach 400%. The mechanical stress change generated in this process makes the negative electrode material collapse, the electrode structure is unstable, and the SEI film on the negative electrode surface is unstable and unsteady. In addition, Si is a semiconductor, and its conductivity is low, and the expansion and contraction of Si nanoparticles also causes them to gradually break away from the transport network of electrons and particles, further reducing their conductivity. All these greatly limit the electrochemical performance of Si. How to limit the volume change of Si and better utilize the capacity advantage of Si is the main research direction at present.

Formation mechanism of SEI film on Si-based anode materials

Like graphite anode materials, Si-based anode materials will also form an SEI film at the solid-liquid interface during the formation process. However, during the intercalation and extraction of lithium, the dramatic volume change of Si causes the SEI film to rupture and continuously. generated, resulting in poor battery cycle performance and low Coulombic efficiency. Therefore, the current research focuses on how to limit the volume change of Si through the recombination of materials, so as to exert the capacity advantage of Si.

In many studies, the most involved is the compounding of silicon carbon. In actual production, there are various ways of compounding silicon materials and carbon materials . Among them, the ideal structure is to use cladding and embedded silicon carbon composite structures to help The construct forms a stable SEI film. For example, the core-shell structure formed after coating has a certain buffering effect on the expansion of Si, which makes the SEI film more stable, and also inhibits the agglomeration of Si particles. Only if the volume expansion problem of Si is solved first, and its capacity characteristics can be well exerted, further research as an electrode material will be meaningful.

When the capacity of Si as a negative electrode material is well exerted, the application of Si -based materials in actual production will become a reality. From the perspective of battery production process, it is studied that the properties of the formed SEI film are affected by controlling the parameters of the formation process, and then improve the Only the battery performance is of practical significance.

Half-cells were fabricated in the laboratory, using AFM combined with conventional characterization methods and lithium-ion battery performance testing methods to explore an ideal single-variable parameter range for SEI film formation under the condition of changing the formation current, formation temperature, and cut-off voltage alone; Then, two different variables are combined within the above-mentioned optimal single variable range, and the variable combination and parameter range to form a more ideal SEI film under different combination conditions are explored。

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