The formation mechanism of SEI of lithium battery and the influence of SEI on lithium battery

When the lithium battery is charged and discharged for the first time, a small amount of polar aprotic solvent electrolyte will undergo a reduction reaction to obtain some electrons, which will combine with lithium ions and the interface film thickness is about 100-120nm, SEI. SEI is usually formed at the solid-liquid interface between the electrode material and the electrolyte. When the lithium battery starts to charge, the lithium ion enters the electrolyte from the active material of the positive electrode, can penetrate the cell membrane, enter the electrolyte, and finally insert into the gap of the layered carbon negative electrode material, and the lithium ion completes a complete unimbedding behavior. At this point, electrons come out of the positive electrode, out of the outer ring, and enter the negative carbon material. Redox reactions occur between electrons, solvents and lithium ions in the electrolyte. After the solvent molecules get electrons, they combine with lithium ions to form SEI, generating H2, CO, CH2 and other gases. As the thickness of the SEI increases, a passivation layer is formed until the electrons cannot penetrate, inhibiting the redox reaction. 2. What are the components of SEI? The thickness of SEI is about 100-120nm, and its composition varies with the composition of the electrolyte. It is generally composed of Li2O, LiF, LiCl, Li2CO3, lico2-r, alkoxides and non-conductive polymers. It is a multi-layer structure, which is porous near the electrolyte and dense near the electrode. 3. The impact of SEI on lithium batteries? The use of SEI should be analyzed from its own characteristics, namely: SEI is the interface layer between the electrode material and the electrolyte, which separates the two. (2) It has the characteristics of a solid electrolyte; lithium ions can pass through (a good conductor of lithium ions), but electrons cannot. SEI plays an important role in the performance of carbon anode lithium batteries. First of all, SEI is completed during the first charge and discharge, resulting in lithium ion consumption. The consumption of lithium ions increases the irreversible capacity of the battery and reduces the charge and discharge efficiency (coulomb efficiency) of the electrode material. Secondly, the SEI film is insoluble in organic solvents and can stably exist in the organic electrolyte solution. A part of the computer is found to exist in the electrolyte, and the anode material is embedded in the PC electrode material. It is easy to damage. If appropriate additives can be added to the electrolyte to promote the formation of SEI, it can effectively prevent the embedding of solvent molecules and prevent the embedding of damaged molecules caused by the solvent. Material, thereby greatly improving the cycle performance and service life of the electrode. Third, SEI allows lithium ions to pass through, but prohibits electrons from passing through. On the one hand, it ensures the continuity of the rocker's charge and discharge cycle, and on the other hand prevents the further consumption of lithium ions and increases the battery life. 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 article: How does battery management IC affect vehicle performance?