On the characteristics analysis and tab design of an 18650 type cylindrical LiFePO4 battery

Lithium-ion (Li-ion) battery is the most promising power source for electric vehicles (EVs) due to its superior advantages of a higher power density, longer lifespan, and lower self-discharge rate. The driving capacity of EVs is critically dependent on the battery performance. In the paper, a fully coupled two-dimensional (2D) electrochemical-thermal model for a commercial 18650 cylindrical lithium iron phosphate (LiFePO4, LFP) battery that considers the contact resistance between the current collectors and electrodes is developed to describe the Li-ion battery performance. The model is validated by experimental data, and is then used to explore local detailed electrochemical-thermal characteristics under different discharge rates and the effects of the tab design. The electrochemical phenomena include the edge effect, which represents the inhomogeneity inside the battery, and the polarization voltage, which depends on both the depth of discharge (DOD) and discharge rates. It is revealed that the polarization heat and the heat generated from the positive electrodes are dominant under a low discharge rate. The ohmic heat and contact resistance heat, as well as the heat generated by the positive current collector, become the most important at a high discharge rate. The effects of the tab design on the battery performance are further investigated, and it is found that the design with the positive tab arranged in the middle of the positive current collector exhibits a much better performance than the traditional design; its maximum temperature is 4.8 °C lower, its voltage platform is 0.05 V higher, and its internal resistance is 5.5 mΩ lower under the 5C discharge rate.