Lithium-ion battery pack thermal management under high ambient temperature and cyclic charging-discharging strategy design

To ensure the stable operation of lithium-ion battery under high ambient temperature with high discharge rate and long operating cycles, the phase change material (PCM) cooling with advantage in latent heat absorption and liquid cooling with advantage in heat removal are utilized and coupling optimized in this work. Based on the preferred hybrid cooling scheme, the two layers cold plates and fins are arranged, and the cold plate structure is redesigned to optimize cooling system. The coupling effects of composite PCM and water flow rate, as well as charging and discharging strategy, are numerically studied. The results show that the hybrid cooling is more suitable to high discharge rate of 5C and long-term cyclic operation at 40 degrees C. The two layers cold plate and fins arranged in hybrid cooling system can mitigate the temperature non-uniformity of batteries along the axis, and the maximum temperature T-max and temperature difference Delta T-max are reduced by 4.44 degrees C and 4.17 degrees C, respectively. Also, the optimized cold plate can mitigate the temperature non-uniformity caused by battery dispersion, and the standard deviation of temperature of batteries is reduced from 0.48 to 0.37. Then, the composite PCM added with expanded graphite can further decrease the T-max and Delta T-max by 2.18 degrees C and 1.79 degrees C, respectively. Lower charging rate offers more reliable cooling performance during continuous cyclic operations. In general, the designed fin-enhanced hybrid cooling system with composite PCM and two layers cold plate can control the T-max and Delta T-max within 45.85 degrees C and 3.39 degrees C at 40 degrees C ambient temperature and 5C discharge respectively, and offers a reliable and desired cooling performance during continuous charging and discharging of 1C, 2C and 3C. During cyclic operation with 3C discharging and 1C charging, the T-max and Delta T-max can be controlled below 44.39 degrees C and 2.64 degrees C, respectively.