Investigation of new phase change material based thermal management systems for Li-ion batteries

Abstract

In this thesis, a battery pack consisting of three A123 20Ah cells connected in series is tested with various cooling methods at different discharge rates. Four different coolant inlet temperatures are selected for the investigation. The results from the battery pack tests at no cooling show that the surface temperature of the battery increases with an increase in discharge rate. The highest average temperature of the battery pack is 56.5°C, corresponding to no cooling case at a high discharge rate. With cold plates, the battery temperature remains in the specified temperature range at all discharge rates, when the coolant temperature is 30°C. The results show that the thermal management system developed in the present study using 6 mm thick phase change composite plates can manage the battery temperature in the required range. n-Octadecane and polyurethane foam are used to make 3 mm and 6 mm thick plates. The battery pack is tested with the developed phase change material based plates. Carbon nanotubes are used to improve the thermal conductivity of the phase change material, along with polyurethane foam. The results show that 3 mm thick plates made from pure phase change material, 3% (wt.) Carbon nanotubes and polyurethane foam can maintain the battery temperature within the required range at all discharge rates. The internal resistance of the cylindrical and prismatic Li-ion batteries is measured at different states of charge and operating temperatures. The obtained results are used to develop a model for the battery pack in MATLAB Simulink. The good agreement attained between the simulation results and the experimental data shows that the developed model can be used to predict the behaviour of Li-ion batteries with reasonable accuracy. An economic analysis shows that the material cost of the developed PCM-based passive thermal management system for a complete battery pack on a lab scale will be approximately $4500. The material cost of the developed thermal management system is reduced by approximately 44% when carbon nanotubes are used with the pure PCM and can be further reduced with production on an industrial scale. A preliminary optimisation of the developed system is performed using a genetic algorithm to maximise the driving range of the vehicle.