Risk assessment and response methods for the application of power lithium batteries

　　Lithium batteries may encounter risks such as collisions, overcharging, overdischarging, short circuits, etc. during actual use, leading to thermal runaway and even causing fires and explosions. As the energy density of a single battery increases, the safety risk increases and the energy released by thermal runaway increases. Most accidents are caused by fires and on-site evidence burning, making it difficult to find the exact cause of the accident. In October 2019, a small fire broke out in the battery room of the Norwegian ferry company Norled MFYtteroyningen, and the cause of the accident is unknown. However, power battery fires usually begin with thermal runaway of one or more batteries.

　　Whether the battery is damaged by external forces (such as impact, compression, needle puncture, rupture, etc.) or internal factors (such as structural damage caused by battery aging, overcharging of battery bulges, diaphragm defects, impurities, burrs, wrinkles, etc.). May cause internal short circuit, release a large amount of energy in a short period of time, and cause a sharp rise in battery temperature, resulting in serious consequences. According to the causes of thermal runaway in power batteries, prevention methods mainly include optimizing battery materials and preventing and managing external environments.

　　(1) The optimization of battery materials mainly involves blocking the occurrence of thermal runaway and improving the battery's ability to withstand thermal runaway through the optimization of battery materials. Starting from the four main materials of the battery (positive electrode material, negative electrode material, separator, electrolyte), such as using lithium iron phosphate with high thermal stability as the positive electrode material, analyzing the proportion of each element in the positive electrode material, improving the thermal stability of the battery, adding flame retardants to the electrolyte or developing solid polymer electrolytes, and selecting separators with higher strength and higher breaking temperature. The optimization of battery materials can fundamentally improve the safety performance of batteries, but it also affects the performance of batteries to a certain extent.

　　(2) The external risk prevention measures for battery thermal runaway mainly include three aspects: structural prevention, BMS monitoring, and thermal management prevention, such as improving the mechanical structure and protection level of the battery pack; Increase the spacing components between batteries or modules to prevent thermal conduction between them; Choose air cooling, water cooling, oil cooling, etc. to alleviate the damage of thermal runaway to the battery; Add a power management system (BMS) to ensure that the battery is in a healthy working state through real-time monitoring of battery capacity, battery charging and discharging, battery temperature, and other measures, and issue warnings to the system before system errors and thermal runaway occur.

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