Thermal Characteristics Analysis Of Vehicle Power Battery And Thermal Runaway Propogation Suppression Of Liquid Cooling Method

As a key component of electric vehicles,the performance of power batteries directly affects the performance of electric vehicles.Temperature is one of the most important factors affecting the charging and discharging performance,cycle life and safety of power batteries.When designing an effective thermal management system,it is necessary to deeply understand the thermal behavior and thermal characteristics,obtain the internal core temperature,determine the thermal properties of the battery,and comprehensively consider the safety of the battery when it occurs thermal runaway.In this paper,the research focus on four aspects:battery thermal model and physical property parameter measurement,the method of internal temperature measurement of battery,liquid cooling battery module heat dissipation characteristics and simulation,and the suppression method of battery thermal runaway propagation.A kind of commercial square large-capacity ternary(NCM)lithium ion battery is taken as an example to systematically study the battery heat problem,from the battery cell to the battery module,from the thermal problems of the normal working state of the battery to the suppression method of the thermal runaway of the battery.(1)In the battery thermal model and physical property parameter measurement,a threedimensional thermal model of the battery cell was established based on the energy balance equation of battery system developed by Bernardi.The key parameters of the battery thermal model were measured,including the internal resistance,the specific heat capacity,the thermal conductivity of three directions,the entropy coefficient,and the open circuit voltage and operating voltage of the battery.The accurate measurement of the model parameters ensures the calculation accuracy of the battery thermal model.(2)In terms of internal temperature acquisition of the battery,a new method of embedding thermocouples inside battery cells was developed for the problem that the internal temperature of the large-capacity prismatic battery is difficult to obtain.The feasibility of the method was verified by comparing the basic characteristics of the battery with or without embedded thermocouples.Moreover,the accuracy of the battery thermal model was fully verified using experimental internal and surface temperatures data of the battery.This method of embedding thermocouples inside battery cells is important for studying the internal and surface temperatures of the large-capacity prismatic batteries and the design of battery thermal management.(3)In the heat dissipation characteristics of the battery liquid cooling module,based on the three-dimensional thermal model of the battery cell,a simulation calculation model of the battery liquid cooling module is established.The liquid cooling cycle experimental circuit was established,and the battery liquid cooling module was designed and processed.Under the conditions of natural convection and liquid cooling condition,the temperature rise experiments of the battery module were carried out.Comparing the experimental results with the model calculation results,the accuracy of the thermal model of the battery liquid cooling module was verified.Using the validated model,the battery liquid cooling module is optimized,so that the maximum temperature of the battery module charging at 3C rate is reduced by 4.7°C.(4)In the suppression method of battery thermal runaway propogation,based on the battery liquid cooling cycle experimental system,the aerogel insulation layer and the liquid cooling plate heat dissipation device are used to modify the battery modules.And the thermal runaway propogation experiments were conducted using the modified battery modules.The effects of increasing the aerogel insulation layer,increasing the heat sink of the liquid cooling plate and combining the two to the thermal runaway propagation of the battery were compared.The results indicate that:(a)the aerogel insulation layer can delay the time of poropogation between the two cells from 84.6s to 386 s,which greatly increases the passengers' escape time,but it still can not completely inhibit the occurrence of thermal runaway propogation;(b)Using liquid cooling plate has no significant effect on the thermal runaway propagation of the battery;(c)the thermal insulation capacity of the aerogel insulation layer and the heat dissipation capability of the liquid cooling plate heat dissipation structure are used to successfully suppress the thermal runaway propogation of the battery.It has very important guiding significance for improving the safety of electric vehicles.