Lithium Ion Battery Fire and Explosion

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pressure and the exothermic heats heat up the system. With the rising up of the battery temperature, more chemical reactions occur, and more heat generation. Once the heat generation is greater than the heat loss, the battery system will undergo ‘temperature of no return’, then the thermal runaway. The heat generation is decided by the materials, and the heat loss decided by the battery can. The latter is changing with the ambient temperature and other related considerations. An elegant way to visualize thermal runway reactions is in the plots often referred to as Semenov plots [8] in Fig. 4. The curved line, 4, represents the heat generation due to an exothermic reaction (exponential function, assuming Arrhenius law) while the straight lines represent the heat removal which is a linear function (Newton's law of cooling) at different coolant temperatures. The temperature of the coolant can be sufficiently low (case of line 1) or insufficiently, like in case 3 where thermal control is not possible under any circumstances. Line 1 has two points of intersection with line 4. Isothermal operation is possible in both points. The lower point E of intersection is a stable point. If temperature deviates upwards cooling power is higher than power generated by the reaction thus the system will return to the temperature of the stable point of operation. If temperature drops, as power generation is higher than power removal temperature will again return to that point. The second (higher point F of intersection), however, is an unstable one. If temperature drops it will carry on dropping until it reaches the stable point, as power removal is higher than power generation, but if it deviates upwards the runaway is inevitable. Line 2 has one tangent point D with line 4, this point is a critical point, as power removal is equals to power generation, and thus, this critical equilibrium temperature is called the ‘Temperature of No Return’. The temperature B is called the self-accelerating decomposition temperature (SADT).
Fig. 4. Thermal diagraph of a reaction and heat loss from a vessel, at 3 ambient temperatures, A, B, and C. A can control the sample to temperature T1, B is at the critical temperature TNR and C cannot control the thermal runaway.
In lithium ion battery, a charged (4.2 V) 2032 battery was tested by C80 micro calorimeter at elevated temperature. The charged battery was disassembled, and the total reactive mass of the battery working materials is 178 mg, which consist of 106 mg 1 M LiPF6 in EC+DEC (1:1 w/w) electrolyte, 34 mg delithiated Li0.5CoO2, 35 mg intercalated Li0.86C6, and 2.5 mg separator. The whole heat flow of the battery reactive materials was shown in Fig. 5. By integrating the elevated heat flow curve of the battery, the reaction heats ∆H can be easily calculated as ∆H=1036 J·g-1. Based on the Arrhenius law, and assuming the reaction order is one, the pre-exponential factor (A) and activation
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