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　　Risk analysis and response methods for the use of power lithium batteries

　　Lithium batteries may encounter risks such as collisions, overcharging, overdischarging, short circuits, etc. during actual use, which can cause thermal runaway and even lead to fire and explosion. With the increase of energy density of individual batteries, safety risks also increase, and the energy released by thermal runaway is also higher. However, most accidents burn on-site evidence due to the large fire, making it difficult to find the accurate cause of the accident. In October 2019, a small fire broke out in the battery room of the "MF Ytteroyningen" passenger ship under the Norwegian ferry company Norled, and the cause of the accident is unknown. But a fire in a power battery usually starts with one or several battery cells experiencing thermal runaway.

　　Whether the battery is damaged by external forces (such as collision, compression, needle puncture, rupture, etc.) or internal factors (such as structural damage caused by battery aging, overcharging leading to battery bulges, diaphragm defects, impurities, burrs, wrinkles, etc.), it is possible to cause internal short circuits, release a large amount of energy in a short period of time, and cause a sharp rise in battery temperature, resulting in serious consequences. The prevention measures for thermal runaway of power batteries mainly include optimization of battery cell materials and prevention and management of external environment.

　　(1) The optimization of battery cell materials mainly relies on the optimization of battery cell materials to block the occurrence of thermal runaway and improve the heat resistance of the battery cell. It mainly starts from the four main materials of the battery cell (positive electrode material, negative electrode material, separator, electrolyte), such as using lithium iron phosphate with higher thermal stability as the positive electrode material, analyzing the proportion of each element in the positive electrode material to improve the thermal stability of the battery cell, adding flame retardants to the electrolyte or developing solid polymer electrolytes, and using separators with higher strength and higher breaking temperature. Optimizing battery cell materials can fundamentally improve the safety performance of batteries, but it also affects the performance of batteries to a certain extent.

　　(2) The measures for external risk control of battery cell thermal runaway mainly include structural prevention, BMS monitoring, and thermal management prevention, such as improving the mechanical structure and protection level of battery packs; Add spacing components between battery cells or modules to prevent thermal conduction between them; Using air cooling, water cooling, oil cooling, etc. to reduce 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 level, battery charging and discharging, battery temperature, and other measures, and issue warnings to the system before system abnormalities or thermal runaway occur.

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