Analyze the charging and discharging characteristics of lithium batteries

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 discharging, Li returns to the positive electrode LiCoO2, but a part of Li must remain in the center of the negative electrode C6 after the formation. In order to ensure the normal insertion of Li in the next charge and discharge, otherwise the battery cell will be overwhelmed 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 a lithium-ion battery will still decrease after multiple charging and discharging, and the reasons are complex and diverse. The important thing is the change of the positive and negative materials. From the molecular level, the hole structure of the positive and negative electrodes will gradually collapse and block; from the chemical point of view, it is the active passivation of the positive and negative materials, and side reactions appear to form stable Other compounds. Physically, the positive electrode material will gradually peel off. In short, the number of lithium ions that can move freely during charge and discharge in the battery is ultimately reduced. Overcharge and overdischarge will cause permanent damage to the positive and negative electrodes of lithium-ion batteries. From a 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. Overcharging will force too much lithium ions into the carbon structure of the negative electrode, and some of them can no longer be released. Unsuitable temperature will trigger other chemical reactions inside the lithium-ion battery to generate compounds that we do not want to see. Therefore, a protective temperature-controlled diaphragm or electrolyte additive is installed between the positive and negative electrodes of many lithium-ion 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 opens, 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 post: What is the reason why lithium-ion battery negative electrode uses copper foil and positive electrode uses aluminum foil