Abstract: Firstly, the layout scheme and 3D model of water cooling system are established. Then the cooling effect and thermal equilibrium of cylindrical lithium-ion battery 18650 in water-cooled mode with different arrangements are comparatively analyzed. Finally, the temperatures at different points of battery module in discharge process are measured. Heat ratio is defined to quantitatively describe the thermal equilibrium of battery module. The results of simulation analysis and test verification show that when the geometric model and cell number of the battery module are the same, the cooling effect and thermal equilibrium of the battery module with staggered arrangement are better than that with parallel arrangement. Under 1C discharge rate, the highest temperature rise of the battery module with staggered arrangement is 2.26 K lower than that with parallel arrangement, with thermal equilibrium improved by 33.9%. In the same arrangement, the more the number of battery cells, the worse the thermal equilibrium of the module. When the number of cells in the module increases from 15 to 60, its thermal equilibrium with parallel arrangement lowers by 5.1%, while that with staggered arrangement lowers by 6.3%, and geometric model and discharge rate have little effects on thermal equilibrium.

Key words: cylindrical lithium-ion traction battery, thermal equilibrium, water cooling system, staggered arrangement, parallel arrangement, heat ratio