| As people demand more and more strong lightweight electron devices, electric vehicles and battery driven tools, an advisable and increasing need appears for battery systems to availably fit these essential energy density and power density demands when operating. Due to their high voltage, high energy density, high power density and insignificant fade in power and capacity after cycles, lithium-ion batteries become the prevalent choice utilized in extensive applications, significantly in the use of electric vehicle. Nevertheless, operating in a high output power and manufacturing the lithium-ion battery packs with greater capacity density result in elevated operating temperatures, which brings about swift fade of capacity after continuous charge/discharge cycles and fade in total output power as well. The battery thermal management system relates deeply to the operating and safety issues of the battery. According to the difference of the heat transfer medium, the lithium-ion battery thermal management can be divided into three types: air cooling, liquid cooling and phase change material cooling. Among them, first two types are the active thermal management and the third one is passive thermal management. Although active thermal management systems are efficient enough in transferring heat away from the battery surface, their size which occupies a large amount of space and complexity are inhibited in applications for example portable electronics and battery-power tools. Passive thermal management systems provide briefness in design that mitigates the need for mechanical devices and additional power to operate them. But a uniform phase change material can't handle the trade-off between the average temperature and total heat storage capacity. In this research, to overcome the shortcoming of uniform PCM cooling, a hierarchical structure is developed. Low, medium and high melting point PCM are combined together in a hierarchical structure to adapt well to the different situations of thermal management. Several simulation researches are conducted in the Workbench and experiments under same conditions are processed to verify the simulation results. |
