Analysis on the hidden dangers of lithium-ion batteries

The frequent explosions of mobile phone batteries are due to the failure of the protection circuit on the one hand, but more importantly, the material has not fundamentally solved the problem. The lithium cobalt oxide cathode active material is a very mature system in terms of small cells, but after fully charged, there is still a large amount of lithium left in the positive electrode. When overcharged, the lithium remaining in the positive electrode will rush to the negative electrode. The formation of dendrites is an inevitable result of overcharging of batteries using lithium cobalt oxide materials. Even in the normal charge and discharge process, there may be excess lithium free to the negative electrode to form dendrites. The theoretical ratio of lithium cobalt oxide materials is The energy is more than 270 milliampere hours per gram, but in order to ensure its cycle performance, the actual use capacity is only half of the theoretical capacity. During use, the battery charging voltage is too high due to some reasons (such as damage to the management system), and a part of the remaining lithium ions in the positive electrode will be extracted, and the electrolyte will deposit on the surface of the negative electrode in the form of metal lithium ions to form dendrites. . The dendrites pierce the diaphragm and form an internal short circuit. The important component of the electrolyte is carbonate, which has a very low flash point and low boiling point, and will burn or even explode under certain conditions. If the battery is overheated, the carbonate in the electrolyte will be oxidized and reduced, and a large amount of gas and more heat will appear. If there is no safety valve or the gas is too late to be released through the safety valve, the internal pressure of the battery will rise sharply and cause an explosion. The polymer electrolyte lithium ion battery does not fundamentally solve the safety problem. It also uses lithium cobalt oxide and organic electrolyte, and the electrolyte is colloidal, not easy to leak, and will burn more violently. The combustion is a polymer battery. The biggest problem with security. There are also some problems in the use, the battery will have an excessive current of several hundred amperes when an external short circuit or an internal short circuit occurs. When an external short circuit occurs, the battery is discharged with a large current instantaneously, which consumes a large amount of energy on the internal resistance and generates huge heat. The internal short-circuit forms a large current, and the temperature rise causes the diaphragm to melt, and the short-circuit area expands, thereby forming a vicious circle. In order to achieve a high working voltage of 3～4.2V for a single cell, a lithium-ion battery must use an organic electrolyte with a decomposition voltage greater than 2V. The organic electrolyte will be electrolyzed under high current and high temperature conditions, and the electrolysis will produce gas. Causes the internal pressure to rise, severely breaking the shell. Overcharging may precipitate metallic lithium ions. In the case of a shell rupture, it will be in direct contact with the air and cause combustion, and the electrolyte will ignite at the same time, a strong flame will occur, the gas will expand rapidly, and an explosion will occur. In addition, regarding mobile phone lithium-ion batteries, due to improper use, such as squeezing, impact and water ingress, the battery swells, deforms and cracks, etc., which will cause the battery to short-circuit and cause an explosion due to heat release during discharge or charging. 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: Analyze the application of lithium-ion batteries in various fields