No abstract

The energy and power densities of lithium-ion batteries (LiBs) are bound to improve in the future. To use such high-performance battery systems as the power source of electric vehicles, the safety and the stability of these systems need to be guaranteed and abnormal heat emissions should not lead to thermal runaway. In this study, we have developed a prototype hybrid cooling system combined with a phase-change material and heat pipes to control abnormal heat emissions in LiBs. The system was built using paraffin wax as the phase change material, heat pipes, and an electric heater modeled on A4-sized laminated-type LiBs pack. We conducted some experiments using this system under conditions that would result in abnormal heating and thermal runaway. As a result, we were able to confirm that the time needed to reach temperatures leading to thermal runaway in the modeled battery pack was extended to 708 seconds by adopting our proposed cooling system, from 104 seconds in the case with no cooling device. A numerical analysis of the heat balance and thermal distribution was also calculated. The calculation results confirmed the thermal behavior in the experimental system, and we investigated the effect of the heat pipes and PCM. The issues that need to be solved to make practical use of the cooling system were also clarified by those discussions. Tatsuya Yamada, Koshiyama, Yoshikawa, Takashi Yamada and Ono, Journal of Thermal Science and Technology, Vol.12, No.1 (2017) damage is done to their internal structure when they reach 80 °C-85 °C (Hammami et al., 2003). These problems must be solved to improve the safety of EVs; therefore, it is necessary to determine what heat control technologies could be used.In this study, we aimed to mitigate thermal runaway by developing a prototype of a hybrid cooling system that combines phase-change materials (PCM) and heat pipes to control abnormal heat emissions from an LiB. This prototype system is intended for A4-sized laminated-type LiBs built with a paraffin wax PCM and heat pipes. We conducted experiments using this system at temperatures that would generally result in thermal runaway. Moreover, we performed a numerical analysis of the heat balance and thermal distribution during abnormal heating. With the help of the calculation results, the thermal behavior in the experimental system was studied and the effect of the heat pipes and PCM were discussed. Lithium-ion battery hybrid-cooling system 2.1 Lithium-ion batteryLiBs are a type of secondary batteries that use graphite as the cathode and, for example, lithium-cobalt oxide (LiCoO 2 ), lithium-manganese oxide (LiMn 2 O 4 ), or lithium iron phosphate (LiFePO 4 ) as the anode. As such, these systems have a simple structure, high electrical conductivity and no memory effect, which means that the LiBs can be lightweight, small, and have high energy density. Recently, LiBs have been adapted for small electronic equipment such as personal computers and smartphones. LiBs, however, have quite poor thermal stability and, t...