Research On Thermal Management System Of Lithium-ion Battery Pack For New Energy Vehicles

Under the pressure of energy shortage and environment pollution all over theworld, new energy vehicles, with the advantages of energy saving, environmentfriendly and high energy efficiency, have won a lot of attention. As the main energystorage component, rechargeable lithium-ion batteries determine the future directionof new energy vehicle due to their high specific energy, high specific power, highenergy density, high discharging voltages and long cycle life relative to otherrechargeable batteries. However, lithium-ion batteries produce a lot of heat duringcharging and discharging, which will bring about a great temperature rise in batterymodules and inhomogeneous temperature difference, thus resulting in injury of thesafety and performance--All challenges are coupled to thermal effects in the battery.So, to optimize the performance of lithium-ion batteries and modules, the thermalmanagement strategies of Lithium-ion batteries are necessary.In order to achieve a good balance between performance and life, the thermalmanagement system of Lithium-ion batteries should maintain the optimum operatingtemperature range for every cell and all batteries modules and keep the temperaturedifference among the modules within a small bound, causing no significant uniformityin battery modules. In this thesis, based on the computational fluid dynamics (CFD), acommercial finite-element software (FE), ANSYS Fluent, was used to simulate thethermal behavior and temperature field of Lithium-ion battery modules under thenatural conditions, then the thermal management systems of the forced air and PCMwas established to research the cooling performance of both the systems.The main jobs in this thesis include:(1) According to the mass, momentum and energy conservation equations, athree-dimensional and transient of heat dissipation model for lithium-ion battery packwas established. Both the heat generation theory and thermal behavior of Lithium-ionbattery modules were analyzed. Simulation results showed that under the natural aircooling condition, the temperature field of the battery pack could not be kept in theoptimal operating temperature range. (2) The simulation models of the active cooling and passive cooling system werebuilt respectively. The results showed compared to the forced-air cooling, the passivecooling system, without additional fan power, could maintain the battery module inoptimum operating temperature range.(3) The effectiveness of passive cooling by PCM was compared with that offorced-air cooling at the same discharge rate and ambient temperature. Theinvestigated results showed that under the abuse conditions, such as the highdischarge rate and ambient temperature, the PCM cooling system, rather than theforced-air cooling system, would be able to meet the operating requirement.