Thermal Characterization of Li-Ion Phosphate (LiFePO4) HEV Battery Using HPPC Test

Recently, Hybrid electric vehicles have become significant. Electric vehicle is still in its infancy while grappling with multiple solutions to its problem of range anxiety and heavy weight. It makes HEV the viable and intermediate solution which can facilitate the transition. The battery behaviour is grossly defined by its dependence on variation due to temperature change. Hence, this present work focuses on understanding thermal characterization & pure behaviour of the Li-Ion Phosphate (LiFePO4) P1-HEV battery using the HPPC test. This becomes imperative because of the varying driver demands and ambient temperatures over the use during the day. Thus, the current drawn from battery varies (different C rate) leading to heat generation (I2R heating) within the pack/individual cell. Cyclically, impacting the cell performance and battery cycle life. This work does the deep drive of, design & modelling the battery pack, heat generation calculation & HPPC profile generation for LiFePO4 single cell obtain the temperature increment in the battery pack corresponding to inertial resistances. The RC values are obtained from the HPPC test which are integrated with the equivalent circuit modelling to get the heat generation values at different C rates. These heat generation values are then used to simulate the single cell & understanding its pure thermal behaviour. This experimental work concludes that heat generation values cannot be taken as just ohmic heat and reaction heat. Dynamic heat generation (obtained from HHPC Test) is far more accurate than that of the analytical heat generation. With this dynamic heat generation and temperature values (obtained from fluent simulation) shows that there is no need of liquid cooling system since only 15 to 20 deg Celsius temperature increment is happening. Air cooling system will be best suitable considering thermal and design aspects for this 2-W HEV.