Modelling of temperature dependent impedance in lithium ion polymer batteries and impact analysis on electric vehicles

The objective of this work is to demonstrate a temperature-dependent impedance model for high-power lithium-ion polymer cells used in modern Electric Vehicles (EV). The impedance model is combined with a self-heating thermal model for system simulations, in order to predict the impact of different cell types on the overall EV performance, under real-world urban and highway drive-cycles. Measurements show that the internal resistance is almost doubled when the ambient temperature is lowered from 20° C to 5°C. This has a drastic impact on the EV´s ability to satisfy the load current requirements without performance lags, and justifies the importance of the modelling approach. When operating in cold climates, it is observed that the Battery Thermal Management System (BTMS) must strike a balance between EV range and performance, as the stored energy should be optimally distributed between the propulsion and heating systems.