Analyze the formation mechanism of SEI film of lithium battery

SEI film formation mechanism of lithium-ion batteries 1. Under a certain negative electrode potential, lithium ions reaching the electrode/electrolyte liquid phase interface and the solvent molecules, lithium ions, additives and even impurity molecules in the electrolyte occur at the electrode/electrolyte liquid phase interface Irreversible reaction. The reaction between the cathode of lithium ion battery and the electrolyte 2. The irreversible reaction mainly occurs when the battery is charged for the first time; 3. When the electrode surface is completely covered by the SEI film, the irreversible reaction stops 4. Once a stable SEI film is formed, charge and discharge The process can be repeated 5. When the battery is charged for the first time, before Li+ intercalation, a dense Li+ permeable SEI film is formed on the surface of the carbon negative electrode. Two-electron reaction: PC/EC+2e-propylene/ethylene+CO₃square¯ Company₃square¯+Li﹢-Li₂Company₃Alkyl lithium carbonate single-electron reaction: PC/EC+e→PC+/EC+radical 2PC/EC-radical+2Li﹢propylene/ethylene+alkoxy carbonic acid Lithium Alkoxy Lithium Carbonate+H₂O-Li₂ Co., Ltd.₂₃++₂(CH₂O) There are two hypotheses about the Li+ conduction mechanism of the SEI film: 1. Light reaches the interface of the SEI film in the liquid, and the lithium salt in the SEI film The cation exchange transfer occurs under the use of the components; 2. The Li+ in the liquid phase is desolubilized through the micropores of the SEI membrane and directly migrates to the electrode body. The formation of the SEI membrane is the result of the mutual use of the carbon anode and the electrolyte, and its stability depends on On the properties of the electrode and electrolyte 1. The influence of electrode interface properties on the stability of SEI membrane 2. The influence of electrolyte composition on the stability of SEI membrane 3. The influence of impurities in the electrolyte 4. The influence of temperature 5. The influence of current density The SEI film is not a simple electrode surface deposition cap layer, the connection structure of the atoms or atomic groups at the interface between the membrane component and the electrode. This is necessary for the realization of the SEI component to ensure a stable weak form of the carbon anode after oxidation and a small amount of non-oxidation. Regular interface,-carboxyl acid group, such as electrode Orly or carboxyl lithium salt group in the process of easy change, make it stably exist in the electrode/electrolyte interface. Graphite oxide can quickly form a stable SEI film in EC, EMC and other electrolytes, thereby reducing the irreversible loss of the electrode. The composition of the electrolyte largely determines the chemical composition of the SEI membrane. With different chemical composition, the structure and performance of the membrane must be different, so the composition of the electrolyte is the key to the performance of the SEI membrane. It is generally believed that under high temperature conditions, the stability of the SEI film and the cycle performance of the electrode will decrease. This is because the dissolution of the SEI film and the co-embedding solvent molecules are accelerated under high temperature conditions, while the SEI film formed under low temperature conditions is dense, stable and low impedance, but the SEI film formed under low temperature conditions is easily decomposed at high temperature. Due to the difference in the diffusion rate and the number of ion migration of different ions, the reduction and decomposition of the electrolyte components on the cathode surface are actually the result of multiple reactions. Therefore, the important forms of electrochemical reactions under different current densities are different, resulting in different film compositions. The results show that the current density has little effect on the thickness of the film, but it can significantly change the composition of the film. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: Types of power lithium-ion batteries and their development profile