Safety has been the primary issue in the use of the lithium ion technology in high energy and high power applications ranging from power tools to electric vehicles. The safety of lithium ion batteries is mainly derived from the thermal effects of the battery during normal and abnormal operation. Overheating may start exothermal reactions that release even more heat which in turn can lead to an accelerated process called a thermal runaway. In addition to the lithium ion batteries of the body factors (electrode materials ^[1], membrane ^[2] and electrolyte ^[3] and other internal materials) as well as the manufacturing process ^[4], the battery aging ^[5] process is also critical to the safety of the lithium ion batteries.

An accelerating rate calorimeter is employed to study the heat release of 5 Ah lithium iron phosphate battery with different aging status under adiabatic condition. We design four aging methods, consisting of cycled at 1 C and 0.5 C, stored at 55 ℃ with SOC 100% and SOC 50%. Thermal behavior of lithium iron phosphate battery charged and discharged at 1C is investigated, and the influence of cycle number, cycle rate, storage time and storage temperature on the overcharge test of lithium iron phosphate battery was studied. The results show that the lithium iron phosphate batteries have no accidents such as leakage, explosion, burning etc, after 600 cycles at 1C or storage for 4 months at high temperature 55 ℃. With the increase of the cycle numbers, the average heat power of the battery charge-discharge and overcharge increases. At the same cycle numbers, the raising range of the temperature and average heat power of the battery cycled at 1 C is decreased, compared with that of battery cycled at 0.5 C. With the increase of the storage time at the high temperature, the average power of the battery charge-discharge and overcharge increase as well. Furthermore, The raising range of the temperature and average heat power of the lithium iron phosphate battery with 100% SOC full power of the battery is smaller than that of battery with 50% SOC. This work was supported by National 863 Program (No. 2013AA050902) and Shanghai Science and Technology Engineering Research Center Program (No. 13DZ2280200).

Reference

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