Research On Thermal Management Of Lithium-Ion Batteries Based On Combination Of Phase Change Materials And Liquid

Resource depletion and environmental pollution are the two major dilemmas faced by human beings in the current development.As a new energy vehicle,electric vehicles are one of the keys to solving the current dilemmas.Power batteries are the energy source of electric vehicles.Among many power batteries,lithium-ion batteries have the advantages of high energy density,light weight,and no pollution,and are widely used in electric vehicles.However,the working performance and service life of lithium batteries are greatly affected by temperature.Excessively high or low temperatures will reduce the charge and discharge capacity of lithium-ion batteries,shorten their service life,and even cause safety accidents.Therefore,in order to ensure that lithium-ion batteries work safely and efficiently within a suitable temperature range,the research and design of lithium battery thermal management systems are of great significance.Firstly,this article introduces the structural characteristics,working principle and the theory of lithium battery heat generation and heat dissipation of lithium batteries.The thermophysical parameters of single 18650 lithium battery were obtained by theoretical calculations.A battery heat generation model based on Bernardi equation was established through CFD simulation technology.The comparison of simulation data and experimental data verified the rationality of the battery heat generation model.Secondly,in order to solve the heat dissipation problem of the lithium battery pack at the extreme ambient temperature of 40℃,a heat dissipation structure of lithium battery pack based on phase change materials was designed.The results show that the poor thermal conductivity of the phase change material and the complete consumption of phase change latent heat leads to thermal runaway of the lithium battery pack,and the maximum temperature and the maximum temperature difference of the battery pack exceed the safe temperature range.A lithium battery heat dissipation structure based on phase change material coupled with liquid was designed to solve the problems,and the influence of different parameters on the heat dissipation effect was studied.The results show that increasing the coolant inlet flow rate can improve the heat dissipation effect.However,when the flow rate is greater than 0.08m/s,further increasing the inlet flow rate improves the heat dissipation effect insignificantly.The heat dissipation effect of the U-shaped flow channel is similar to that of the S-shaped flow channel.Nevertheless,the complex and curved structure of the S-shaped flow channel causes a larger pressure drop.At the same inlet flow rate,the larger the flow channel cross-sectional size,the better the heat dissipation effect of the model and the smaller the pressure drop,but when the flow rate is greater than 0.08m/s,the heat dissipation effects of models with different flow channel cross-sectional dimensions are very similar.Only increasing the number of flow channels without changing the flow direction of the inlet and outlet has little effect on the heat dissipation performance.Increasing the number of flow channels while using staggered flow can reduce the maximum temperature difference of the battery pack.Finally,a lithium battery thermal insulation system based on phase change materials is proposed to solve the problem of heat preservation of lithium batteries in low temperature environments,and the difference in heat preservation effect between the box-type insulation structure and the phase change material-liquid composite insulation structure is compared.The results show that the box-type thermal insulation structure has poor temperature uniformity during the cooling process,and the composite thermal insulation structure is more feasible.In addition,adding an insulation layer can effectively extend the insulation time.