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In the past September, we have been a phone scraper, of course, not iPhone7, but another Samsung phone - Noote7. Because of its battery explosion and the differentiated treatment of domestic and foreign users rather than its strong performance attracted our attention. And now Samsung has stopped in the global Note 7 of the production and sales, opened a recall.
For an electronic device , its strong performance can not cover its security problems. Today let’s study the reasons cause the lithium-ion battery thermal runaway.
For lithium-ion battery, thermal runaway is the most serious security incidents, it will cause lithium-ion battery fire or explosion, a direct threat to the safety of users.
Lithium-ion battery thermal runaway occurs mainly due to internal heat production is much higher than the cooling rate, lithium-ion battery in the internal accumulation of a lot of heat, causing a chain reaction, leading to battery fire and explosion.
There are many factors that cause thermal runaway, in general there are two types, internal and external. Internal factors are mainly: battery production defects lead to short circuit; batteries used improperly, resulting in internal lithium dendrites lead to positive and negative short circuit. External factors such as extrusion and acupuncture and other external factors lead to short-circuit lithium-ion battery; battery external short-circuit caused by excessive accumulation of heat within the battery; external temperature is too high lead SEI film and cathode materials decomposition.
Lithium-ion battery thermal runaway factors can be divided into two, one is the internal heat rate of the battery, the other is the lithium-ion battery cooling rate. Conventional thermal analysis tools generally assume that the heat production of lithium-ion batteries is uniform throughout the volume, so these tools analyze thermal runaway as independent of the thermal conductivity of the cell, as is the case with lithium-ion batteries in practice , So the prediction results are not accurate. Studies have shown that even within the 26650 battery there is a large thermal gradient, so traditional methods and tools can not accurately predict the internal and external thermal state of the battery.