Impact of Vehicle Charge and Discharge Cycles on the Thermal Characteristics of Lithium-ion Batteries
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The performance, life-cycle cost, and safety of electric and hybrid electric vehicles (EVs and HEVs) depend strongly on the vehicle’s energy storage system. Advanced batteries such as lithium-ion (Li-ion) polymer batteries are quite viable options for storing energy in EVs and HEVs. Battery temperature impacts battery performance, SOH, and may even present a safety risk. Therefore, thermal management is essential for achieving the desired performance and life-cycle from a vehicle battery pack comprised of a particular battery cell or module. This work presents the thermal characteristics of a prismatic pouch battery comprised of LiFePO4 electrode material and modules. Characterization is performed via experiments that enable development of an empirical battery thermal model for vehicle simulations. As well electrical data is presented for the validation of electrochemistry based battery thermal models. The research is organized into two parts. Part-I: An apparatus was designed to measure the surface temperature distribution, heat flux, and heat generation from a battery pouch cell undergoing various charge/discharge cycles. In this work, a prismatic lithium-ion pouch cell is cooled by two cold plates with 19 thermocouples and 3 heat flux sensors applied to the battery at distributed locations. The total heat generation from a particular battery is obtained at various discharge rates (1C, 2C, 3C, and 4C) and different cooling bath temperature (5 0C, 15 0C, 25 0C, and 35 0C). Results show that the heat generation rate is greatly affected by the both discharge rate and boundary conditions. The developed experimental facility can be used for the measurement of heat generation from any prismatic battery, regardless of chemistry. Thermal images obtained at different discharge rates are presented within to enable visualization of the temperature distribution. An empirical battery thermal model is developed and validated with collected data from a test bench in terms of temperature, SOC and voltage profile. In part-II: In-situ vehicle data was collected using three data loggers installed in three different Burlington Hydro Ford Escape vehicles (one pure EV and other two HEVs). The data collection infrastructure developed produced monthly reports for the EV, allowing Burlington Hydro to track the vehicle’s distance travelled, energy consumption, efficiency, and charging times. Five months of data for the EV indicated 792.6 km travelled and 222.6 kWh of grid electricity consumed. The real-world drive cycles from the EV were then performed with the lab apparatus and thermal data was collected and analyzed. In this study, a vehicle model using PSAT/Autonomie software is developed based on available specifications of the vehicle and is validated with the collected drive cycle.