Cell And Pack Design For Thermal Optimization Of Ternary Lithium-Ion Battery

In this paper,the discharge and thermal characteristics of 51 Ah Vehicle Lithiumion battery and battery module are studied by simulation and experiment,and suggestions on the optimization of temperature field and consistency are put forward.Three batteries of the same type were used to test the capacity,internal resistance and discharge temperature rise.The results show that the internal resistance of the battery increases with the decrease of temperature.When SOC is low,the battery resistance will increase sharply,and the internal resistance of charging is less than that of discharging.When discharging at low temperature,the capacity of the battery will decrease greatly,and the capacity difference between 10 ℃ and 45 ℃ is about 5 Ah.The average temperature is positively correlated with the discharge rate.The temperature rise can reach 16 ℃ at 1.5C rate and is lower than 3 ℃ at 0.3C rate.When the discharge rate is low,the average temperature of the battery decreases.At the end of discharge,the maximum temperature of the battery appears at the center of the battery towards the positive electrode,and the minimum temperature appears at the positive and negative electrode ears.The internal resistance of the battery is consistent at 25 ℃ and 40 ℃.The variation of capacity difference with temperature is nonmonotonic.A three-dimensional electrochemical-thermal coupling model was proposed to study the current density of the collector,the electrolyte current density at the cross section of the electrode pair and the temperature distribution of the cell.The current density near the tab is the highest in the collector.At the beginning of the discharge,the current density of the electrolyte on the side of the positive electrode tab is the highest,while at the end of the discharge,the current density in the middle region is the highest.With the increase of discharge rate,the uniformity of current distribution becomes worse,and the maximum temperature rise and temperature difference increase.The response surface method was used to adjust the thickness of the positive electrode,the size of the collector and the size of the positive and negative tab.After optimization,the average temperature rise of the battery is reduced by 2.93 ℃,the maximum temperature difference is reduced by 0.596 ℃,and the scheme error is less than 2.68%.The maximum temperature rise of the battery is 6.56 ℃,which is 30.9%lower than that before optimization;the maximum temperature difference is 1.175 ℃,which is 33.7% lower than that before optimization.Based on the electrochemical-thermal coupling model and the circuit model,the effects of different connection modes on the temperature field and consistency of the battery module were studied.The higher the discharge rate,the worse the consistency of the module.The increase of parallel branches or the decrease of the number of series units will reduce the average temperature rise and the maximum temperature difference of the module.At the end of discharge,the battery voltage of series circuit is the highest,and that of parallel circuit is the lowest.When the number of parallel branches is the same,the consistency of series first and then parallel module is better than that of series first and then parallel module.The more the number of batteries in series,the worse the consistency of batteries.The more the number of branches in series then parallel,the worse the battery consistency.