Common failure performance and failure mechanism decomposition

The capacity attenuation is critically divided into two types: reversible capacity attenuation and irreversible capacity attenuation. Reversible capacity decay can restore the lost capacity by adjusting the battery charging and discharging system and improving the battery usage environment. Irreversible capacity decay is an irreversible change in the battery's internal capacity and an irreversible capacity loss. The root cause of battery capacity decay failure is the failure of materials, and it is closely related to objective factors such as battery manufacturing process and battery use environment. From a material point of view, the main reasons for the failure are the structural failure of the positive electrode material, the transitional growth of SEI on the negative electrode surface, the analysis and deterioration of the electrolyte, the corrosion of the current collector, and the trace impurities of the system. (2) Increase in internal resistance. The internal resistance of a lithium battery is related to the internal electron transmission and ion transmission process of the battery system. It is mainly divided into ohmic resistance and polarized internal resistance. The polarized internal resistance is mainly caused by electrochemical polarization. There are two kinds of chemical polarization and concentration polarization. The important factors that lead to the increase of the internal resistance of lithium batteries are divided into key battery materials and battery use environment. Que Yongchun of the University of Science and Technology of my country used synchrotron radiation technology to propose that the jumping mechanism of transition elements is the cause of potential hysteresis and voltage attenuation, indicating that within the battery system, the abnormality of key materials is the fundamental factor influencing the increase of internal resistance and battery polarization. (3) The performance of internal short circuit can be divided into: ① short circuit between copper/aluminum current collectors; ② diaphragm failure loses electronic insulation or gaps become micro-contact between positive and negative electrodes, and local heating is serious, and then the charge and discharge process It may diffuse to the surroundings and cause thermal runaway; ③The transition metal impurities in the positive electrode slurry are not removed cleanly, pierce the separator, or promote the formation of negative electrode lithium dendrites and cause internal short circuits; ④Lithium dendrites cause internal short circuits. In addition, in the process of battery design and manufacturing or battery pack assembly, unreasonable design and excessive local pressure can also cause internal short circuits. Overcharge and overdischarge of the battery will also cause internal short circuits. The main reason is that the current collector corrodes and deposits on the electrode surface. In severe cases, the positive and negative electrodes are connected through the separator. Internal short circuit induced by overdischarge (4) Gas production Lithium battery gas production is critically divided into normal gas production and abnormal gas production. During the battery formation process, the gas production phenomenon that occurs when the electrolyte is consumed to form a stable SEI film is normal gas production. The key to gas production in the formation stage is the emergence of H2, CO2, C2H2, etc. due to ester single/two-electron reactions. Abnormal gas production is only in the battery cycle process, excessive consumption of electrolyte release gas or positive electrode material oxygen release, etc., often appear in soft-pack batteries, resulting in excessive internal pressure and deformation of the battery, breaking the packaging aluminum film, internal Battery contact problems, etc. (5) Thermal runaway Thermal runaway refers to the rapid rise of the internal or overall temperature of the lithium battery, the heat cannot be dissipated in time, and a large amount of heat accumulates inside, and induces further side reactions. In order to guard against serious safety problems caused by thermal runaway of lithium batteries, measures such as PTC, safety valves, and thermal conductive films are often used. At the same time, systematic measures must be taken in battery design, battery manufacturing process, battery management system, and battery use environment. consider. Common thermal behavior inside the battery (6) Lithium evolution Lithium evolution is a relatively common phenomenon of aging and failure of lithium batteries. The form of manifestation is important. A layer of gray, off-white or gray-blue material appears on the surface of the negative electrode. These materials are metallic lithium precipitated on the surface of the negative electrode. Zhang Qiang of Tsinghua University and others pointed out that the important factors that affect dendrite growth are current density, temperature and power. Measures such as adding electrolyte additives, artificial SEI, high salt concentration electrolyte, structured anode, and optimizing battery configuration design to suppress dendrites Growth. Common Lithium Analysis in Failed Batteries Lithium batteries have a wide range of applications, ranging from mobile terminals such as mobile phones and computers to electric buses and large-scale energy storage. Since many fire and explosion accidents of mobile phone electric vehicles occurred at home and abroad, reliability and safety are as important as their performance. my country's failure decomposition has been systematically developed in the field of machinery and aviation, but has not been systematically studied in the field of lithium batteries, and it is still facing many problems. Battery companies and materials companies each carry out research on failure decomposition of lithium batteries, but mostly focus on battery manufacturing processes and materials research and development, with the direct goal of improving battery performance and reducing battery costs. In the future, the research institute and related companies can strengthen cooperation and exchanges, and strive to establish and improve the failure tree and failure decomposition process of lithium batteries. Disclaimer: Some pictures and content of articles published on this site are from the Internet. 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