Study On Thermal Management Of Cylindrical Lithium-ion Batteries Based On Flow Boiling Heat Transfer In Flexible Channels

With the increase of sales of new energy vehicles,the power battery industry has entered a period of explosive development.Lithium batteries are widely used in power systems due to their excellent structural stability,safety performance and long service life.Temperature is a key factor affecting the performance and life of lithium batteries.In this paper,the thermal management of cylindrical lithium-ion batteries is studied in detail.Battery thermal management includes external cooling and internal cooling.Electrodes are the main heat source during charging and discharging,so optimizing the design of electrodes is the key factor to reduce the heat production of batteries.A pseudo-two-dimensional electrochemical-thermal coupling model was established to study the effects of particle size and temperature-dependent parameters of positive and negative electrodes on the heat generation of batteries.The heat production rate of batteries during constant current discharge,as well as the heat production rate and proportion of positive,separator and negative parts were studied.The results showed that the total heat production power varied with the fluctuation of the reaction heat,and the proportion of the reaction heat in the positive electrode layer was the largest.The proportion of polarization heat generation in the negative electrode layer was higher than positive electrode,and the heat generation in the separator was mainly derived from ohmic heat.Under different convective heat transfer coefficients,the difference between surface temperature and internal temperature of the battery was different,so it was necessary to adopt reasonable thermal management measures for the battery.In order to better study the electrochemical characteristics of lithium-ion batteries during discharge,a two-dimensional electrochemical-thermal coupling model was established on the basis of considering the edge effect caused by the winding and stacking of cylindrical batteries.The results showed that the thermal management of flexible metal microchannels can effectively evacuate the heat generated during battery discharge.In order to explore the cooling effect based on the flow and heat transfer in flexible non-metallic tubes,a battery thermal management experimental system was established.The temperature characteristics of cell modules including single cells and battery module were studied with refrigerant R141b as experimental medium.The influence of channel material,heat transfer mode,contact resistance and contact area on cooling effect were analyzed.By calculating the heat transfer coefficient of fins,the method of calculating the heat transfer coefficient of battery surface was obtained.In order to explore the influence of high thermal conductivity channel on the cooling effect of batteries,an experimental study was carried out to design a flexible rectangular flat microchannel aluminum alloy plate as the flow channel.The structure improved the problems of poor contact and high thermal conductivity of flexible non-metallic microchannels.In addition,the contact area with the battery could be achieved by increasing the area of the cold plate or changing the contact center angle.The heat transfer between the cell and the flexible metal microchannel was enhanced.When the inlet mass flow rate was within a certain range,the flow boiling heat transfer in the microchannel could be realized,and better cooling effect could be achieved.