Analysis of the structure and principle of lithium batteries

The structure and principle of the lithium battery The important composition of the lithium battery: (1) The positive electrode active material mainly refers to lithium cobalt oxide, lithium manganate, lithium iron phosphate, lithium nickelate, lithium nickel cobalt manganate, etc. The conductive current collector is generally used in thickness 10--20 micron aluminum foil; (2) Diaphragm is a special plastic film that allows lithium ions to pass through, but it is an electronic insulator. At present, there are two types of PE and PP and their combination. There is also a type of inorganic solid diaphragm. For example, the alumina diaphragm coating is an inorganic solid diaphragm; (3) The negative electrode active material mainly refers to graphite, lithium titanate, or carbon materials with a similar graphite structure. The conductive current collector generally uses a thickness of Copper foil of 7-15 microns; (4) The electrolyte is generally an organic system, such as a carbonate solvent with lithium hexafluorophosphate dissolved, and some polymer batteries use gel electrolyte; (5) The battery shell is mainly divided into hard shells (Steel shell, aluminum shell, nickel-plated iron shell, etc.) and soft package (aluminum plastic film). When the battery is charged, lithium ions are extracted from the positive electrode and inserted in the negative electrode, and vice versa during discharge. This requires an electrode to be in a lithium-intercalation state before assembly. Generally, lithium-intercalation transition metal oxides with a potential greater than 3V relative to lithium and stable in the air are selected as positive electrodes, such as LiCoO2, LiNiO2, and LiMn2O4. As the material of the negative electrode, choose the intercalable lithium compound whose potential is as close as possible to the lithium potential. For example, various carbon materials include natural graphite, synthetic graphite, carbon fiber, mesophase sphere carbon, etc. and metal oxides, including SnO, SnO2, and SnO2. Tin composite oxide SnBxPyOz (xu003d0.4～0.6, yu003d0.6～0.4, zu003d(2+3x+5y)/2) etc. The electrolyte adopts a mixed solvent system of LiPF6 ethylene carbonate (EC), propylene carbonate (PC) and low-viscosity diethyl carbonate (DEC) and other alkyl carbonates. The membrane adopts polyolefin microporous membranes such as PE, PP or their composite membranes, especially the PP/PE/PP three-layer membrane not only has a lower melting point, but also has a higher puncture resistance, which plays a role in heat insurance. The shell is made of steel or aluminum, and the cover assembly has the function of explosion-proof and power-off. Basic working principle When the battery is charged, lithium ions are extracted from the lithium-containing compound of the positive electrode, and the lithium ions move to the negative electrode through the electrolyte. The carbon material of the negative electrode has a layered structure. It has many micropores. The lithium ions that reach the negative electrode are inserted into the micropores of the carbon layer. The more lithium ions are inserted, the higher the charging capacity. When the battery is discharged (that is, the process we use the battery), the lithium ions embedded in the carbon layer of the negative electrode are released and move back to the positive electrode. The more lithium ions returned to the positive electrode, the higher the discharge capacity. What we usually call battery capacity refers to the discharge capacity. During the charging and discharging process of lithium batteries, lithium ions are in a state of movement from positive → negative → positive. This is like a rocking chair. The two ends of the rocking chair are the two poles of the battery, and the lithium ion moves back and forth on both ends of the rocking chair. Therefore, lithium batteries are also called rocking chair batteries. Charging and discharging mechanism The charging process of a lithium battery is divided into two stages: a constant current charging stage and a constant voltage current decreasing charging stage. Excessive charging and discharging of lithium batteries can cause permanent damage to the positive and negative electrodes. Excessive discharge causes the negative carbon sheet structure to collapse, and the collapse will cause the lithium ions to be unable to be inserted during the charging process; overcharging causes too many lithium ions to be inserted into the negative carbon structure, causing some of the lithium ions to be unable to be released anymore. The best charging and discharging method for lithium batteries to maintain performance is shallow charge and shallow discharge. Generally 60% DOD is 2 to 4 times the cycle life under 100% DOD conditions. 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: What are the reasons why BYD switched to ternary lithium batteries?