Battery thermal management model and structure optimization of porous composite phase change material

Abstract

In recent years, with the increasing of energy shortage and environmental pollution, various industries are transforming into green and environment-friendly enterprises. Especially in automotive industry, more and more companies pay attention to the development of electric vehicles. As one kind of energy-supplied devices, lithium-ion battery is a very popular research direction. However, its thermal management problem has always been restricting the development of new energy vehicles. It is vital to solve the heat dissipation problem of lithium-ion battery. The temperature of phase change material (PCM) remains unchanged during phase transition, which makes PCM to be the ideal choice for temperature control device. Nowadays, PCM has been introduced to the thermal management of battery. However, the low thermal conductivity of PCM causes slow heat transfer rate and weakens thermal management performance. It is urgent to improve the heat transfer rate of PCM to achieve better thermal management effect. The high thermal conductivity porous media such as metal foam and expanded graphite are commonly used to prepare composite PCM and enhance PCM thermal conductivity. However, the geometric parameters and arrangements of porous media have great effects on composite PCM thermal performance. The structural optimization combined with the heat generation characteristics of battery should be further carried out to optimize the porous media configuration and obtain better thermal management performance. Based on that, a coupling model with battery heat generation and temperature control with PCM was established in present paper, where the heat generation and transfer process in battery, the heat transfer process in PCM are comprehensively considered. The copper foam/paraffin composite PCM was used as the temperature control material. The effects of PCM layer thickness and porous media on battery thermal management performance were investigated under 5C charge and discharge rate. The results show that filling porous media can effectively improve heat dissipation rate and reduce battery surface temperature. At the same time, the PCM melting rate is enhanced and heat storage density is reduced with filling porous media. When the PCM layer is small, PCM will quickly melt completely, which results in the reduction of effective temperature control time. For example, when the PCM layer thickness is 4 or 5 mm, PCM has already completely melted at the ending of one charging-discharging cycle, which causes the battery surface temperature quickly increasing. Although increasing PCM layer thickness can improve the effective temperature control time and offset the shortcoming of filling porous media, the increase of PCM layer thickness will occupy extra space, which is very unfavorable in the actual electric vehicle. A new model with partially filling copper foam is proposed in present paper to comprehensively consider the temperature control time, temperature control effect and space restriction. In the region near the battery surface, PCM filling with metal foam is used to improve PCM thermal conductivity and temperature control effect, and pure PCM without filling metal foam is used in the region far away from the battery surface to improve thermal storage density and prolong effective temperature control time. Then, structural optimization was performed to the proposed model. The results show that the partial filling copper foam structure with total PCM layer thickness of 6 mm and the 3 mm layer near battery filled with copper foam is the optimum temperature control scheme with comprehensively considering the temperature control time, temperature control effect and space restriction.