Heating Characteristics And Cooling System Design Of Lithium Iron Phosphate Power Battery

Due to the dual pressure of energy crisis and environmental pollution,electric vehicles have become the development trend of today’s automobile industry.As the power source of electric vehicles,lithium-ion batteries have the characteristics of high specific energy,large output power,excellent rate performance,long cycle life,and good safety.However,with the development of electric vehicles,the thermal safety of power batteries has become increasingly problematic.prominent.Lithium-ion batteries will generate a lot of internal heat during long-term cycling.If they cannot be dissipated in time and accumulate inside,the battery’s operating temperature will gradually rise,and high temperature will easily lead to a sharp decline in battery performance and degradation of battery life.Sometimes it will cause safety problems such as fire or even explosion.Therefore,the research on the heating and heat dissipation characteristics of power batteries during use has become an important research topic in the field of electric vehicle design.Based on the electrochemical-thermal coupling model,this paper first studies the thermal characteristics of lithium iron phosphate single cells and battery modules,and analyzes the basic characteristics and main influencing factors of battery heat generation and heat dissipation;on this basis,the battery capacity attenuation is established The model analyzes the characteristics and laws of battery capacity attenuation at different temperatures;finally,based on the heating and heat dissipation characteristics of lithium iron phosphate,the liquid cooling structure of the battery module is designed,and its influence on the temperature field of the battery pack is analyzed,and the liquid is optimized.Parameters and structure of cooling and heat dissipation.The specific research content is as follows:(1)Based on the electrochemical-thermal coupling model,a thermal simulation model of lithium iron phosphate single battery was established,and the effects of discharge rate,ambient temperature and AC heat transfer coefficient on the thermal characteristics of single battery and battery pack were studied and analyzed The impact on the battery temperature field.The results show that the battery discharge rate,convective heat transfer coefficient and ambient temperature have an important influence on the temperature field of single cells and battery packs.The higher the discharge rate,the greater the convective heat transfer coefficient,the greater the battery temperature difference,and the greater the temperature uniformity.Poor,high temperature and low temperature environment make the temperature difference of the battery become larger,and the temperature uniformity becomes worse.(2)Based on the SEI growth theory of the negative electrode of the battery,the capacity decay model of lithium iron phosphate single battery was established,and the influence of the discharge rate,the size of the negative electrode size and the charge cut-off voltage on the battery capacity decay under different temperature conditions was studied,and the temperature on the battery capacity was analyzed.The influence law of the decay process,the results show that:the discharge rate,the negative electrode particle size and the maximum charge cut-off voltage have obvious effects on the battery capacity attenuation.The higher the discharge rate,the greater the charge cut-off voltage,and the faster the battery capacity decays.A smaller particle size can slow down the rate of capacity decay.Increasing temperature will accelerate the occurrence of side reactions inside the battery,reduce the active lithium of the battery,destroy the structure of the positive and negative electrodes,and dissolve metal ions,which will eventually accelerate the capacity decay process and reduce its service life.(3)For 6 soft-packed lithium iron phosphate battery packs,the plate and serpentine elbow liquid cooling structure was designed,and the influence of fluid flow direction,fluid inlet temperature and fluid velocity on the temperature field of the battery pack was analyzed.The results showed that:serpentine The cooling effect of the elbow cooling system is better than that of the plate cooling system.This is because the elbow structure causes the fluid to twist and turn,avoiding the difference in the cooling effect of the inlet and outlet temperature,and improving the temperature uniformity of the battery pack.In summary,this paper studies the thermal characteristics,capacity attenuation and liquid cooling heat dissipation of lithium-ion battery cells and battery packs,and discusses the factors affecting thermal behavior and capacity attenuation,and uses liquid cooling to dissipate heat from the battery pack.And optimize the liquid cooling performance.The research results of this paper provide theoretical guidance for the safe use of batteries.The optimization results of liquid cooling heat dissipation provide a certain reference for the development of battery thermal management strategies,so as to further ensure the performance of the power battery and improve the thermal safety of the battery.