The causes of Pacific Automotive Network lithium-ion battery fires can be divided into two parts: internal causes and external causes. Own causes mainly refer to the thermal stability of its own materials and structures, which affect the occurrence of fires; External causes refer to lithium-ion battery fires caused by various abuse methods.
At the beginning of the popularization and application of lithium power batteries, some accidents occurred due to insufficient understanding of battery performance, lack of experience in their own design and ignorance of the system by users. Additionally, the rise of electric vehicles is still under scrutiny, making the impact of lithium-ion battery fires particularly widespread.
1.1 Specific causes Lithium-ion batteries arecomposed of positive electrode materials, negative electrode materials and electrolytes. The thermal stability of these parts directly affects the possibility of thermal runaway of the battery core.
Factors affecting the thermal stability of negative electrode materials Most of the negative electrode materials currently used are carbon materials. Under high temperature conditions, graphite easily reacts with electrolyte, especially when the battery charge is high, and LiC6 can increase the reaction intensity.
Some studies have shown that the temperature at which the negative electrode begins to react and release heat is related to the particle size of the carbon material. The larger the particles, the higher the temperature at which the reaction begins. and the more it's safe. At the same time, carbonaceous materials of different structures participate in thereaction of the electrolyte and their heat dissipation is different. Graphite releases more heat than amorphous carbon (mainly soft carbon and hard carbon).
Factors affecting the thermal stability of cathode materials. The cathode materials currently widely used for lithium-ion batteries are all lithium compounds. Generally speaking, the safety of lithium iron phosphate, lithium manganate and ternary lithium is rated from high to low. Some people have specifically studied the impact of cathode materials on the safety of these batteries.
Research estimates that the higher the lithium content in the molecular formula of the lithium compound, the worse its thermal stability and the lower the temperature at which it begins to react with the electrolyte. There is a quantitative comparison. The proportion coefficient of each atom in the molecular formulae. When the lithium coefficient is 0.25, the reaction temperature is 230°C; if this value becomes 1, the initial reaction temperature becomes 170°C. In addition, if the cathode material contains other metallic elements than lithium, the cathode material containing a manganese element will have better thermal stability than the cathode material containing a nickel element.
Factors affecting the thermal stability of the electrolyte The electrolyte can be regarded as the core of the thermal stability problem, and its stability directly affects the stability of the entire system. Someone has done research on the thermal stability of the electrolyte. The results show that the higher the content of dimethyl carbonate in the electrolyte, the worse its thermal stability and the easier it is to react with the positive and negative electrode materials; the materials have poor compatibility, this isthat is, they can react with many different salts at lower temperatures, meaning the more active they are, the worse their thermal stability will be.
Thermal aging caused by aging is a complete process. The SEI film structure of the negative electrode ages and is damaged, triggering a self-generated thermal process; the lithium dendrites of the negative electrode accumulate, causing an internal short circuit or internal short circuit. encounter a high temperature environment. The environment reacts violently with the electrolyte. The increase in internal resistance caused by aging increases the likelihood of heat buildup. Overall, there is a positive correlation between aging and the risk of thermal runaway.
1.2 Thermal runaway factors under various abuses Lithium-ion battery abuse generally refers to improper useUse of batteries due to accidents or management system failures.
(Images/Text/Photos: Pacific Automotive Network Calling the Beast Q&A)