What is the principle of lithium batteries?

A power supply charges the battery. At this time, the electron e on the positive electrode runs from the external circuit to the negative electrode. The positive lithium ion Li+ jumps from the positive electrode into the electrolyte, crawls through the small and curved hole in the diaphragm, and swims to the negative electrode. The electrons that ran long ago are joined together. The battery discharge process includes constant current discharge and constant resistance discharge. Constant current discharge is actually adding a variable resistance to the external circuit that can change with the voltage. The essence of constant resistance discharge is to add a resistance to the positive and negative electrodes of the battery to allow electrons to pass through. . It can be seen that as long as the electrons on the negative electrode cannot run from the negative electrode to the positive electrode, the battery will not discharge. Both electrons and Li+ act at the same time, with the same direction but different paths. When discharging, the electrons run from the negative electrode to the positive electrode through the electronic conductor, and the lithium ion Li+ jumps from the negative electrode into the electrolyte, crawling through the small curved hole in the diaphragm. The swim reaches the positive pole and combines with the electrons that have ran over. Charge and discharge characteristics The positive electrode of the battery cell adopts LiCoO2, LiNiO2, LiMn2O2. LiCoO2 is a crystal type with a very stable layer structure, but when x Li ions are removed from LiCoO2, its structure may change, but it does not depend on the change. The size of x. Through research, it is found that when x>0.5, the structure of Li1-xCoO2 is extremely unstable, the crystal form collapses, and its external appearance is the overwhelming end of the battery cell. Therefore, during use of the battery cell, the value of x in Li1-xCoO2 should be controlled by limiting the charging voltage. Generally, the charging voltage is not greater than 4.2V and x is less than 0.5. At this time, the crystal form of Li1-xCoO2 is still stable. The negative electrode C6 has its own characteristics. After the first formation, the Li in the positive electrode LiCoO2 is charged into the negative electrode C6. When discharged, Li returns to the positive electrode LiCoO2, but after the formation, a part of Li must remain in the center of the negative electrode C6. In order to ensure the normal insertion of Li in the next charge and discharge, otherwise the overwhelming of the cell is very short. In order to ensure that a part of Li remains in the negative electrode C6, it is generally achieved by limiting the lower discharge voltage: safe charging upper voltage ≤ 4.2V, lower discharge limit Voltage ≥2.5V. The principle of the memory effect is crystallization, and this reaction hardly occurs in lithium-ion batteries. However, the capacity of lithium batteries will still decrease after repeated charging and discharging, and the reasons are complex and diverse. It is mainly the changes in the positive and negative materials themselves. From the molecular level, the hole structure on the positive and negative electrodes will gradually collapse and block; from a chemical point of view, it is the active passivation of the positive and negative materials, and side reactions appear to be stable. Other compounds. Physically, the positive electrode material will gradually peel off. In short, the number of lithium ions that can move freely during the charge and discharge process is ultimately reduced. Overcharge and overdischarge will cause permanent damage to the positive and negative electrodes of the lithium battery. From the molecular level, it can be intuitively understood that overdischarge will cause the negative electrode carbon to excessively release lithium ions and cause its sheet structure to collapse. Charging will force too much lithium ions into the carbon structure of the negative electrode, and some of them will no longer be able to be released. Unsuitable temperature will trigger other chemical reactions inside the lithium battery to generate compounds that we do not want to see, so there are protective temperature-controlled diaphragms or electrolyte additives between the positive and negative electrodes of many lithium batteries. When the battery heats up to a certain level, the membrane pores of the composite membrane are closed or the electrolyte is denatured, the internal resistance of the battery increases until it is disconnected, and the battery no longer heats up to ensure that the battery charging temperature is normal. 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: What are the differences between various common rechargeable batteries?