Research On Thermal Characteristics Of A Soft Pack Lithium-ion Battery And Design Optimization Of Liquid Cooling Structure

With the severity of energy crisis and environmental pollution,the development trend of automobile industry is changing from traditional fuel vehicles that use fossil fuels as energy sources to electric vehicles.Lithium-ion battery is the preferred energy source for electric vehicles,and the influence of temperature on their performance and life is crucial.High temperature may cause thermal runaway of the battery,making it impossible for electric vehicles to run safely.Therefore,it is necessary to understand the electrical and thermal characteristics of the battery and design an effective thermal management system to control the battery temperature so that the battery can perform at its best,improve battery life and ensure the safe driving of electric vehicles.This paper focuses on the thermal characteristics of lithium-ion battery as well as the design and optimization of its liquid cooling structure.The main work is as follows:(1)The capacity test,temperature rise test,internal resistance test and entropy thermal coefficient test of the soft pack lithium-ion battery were conducted to analyze the variation characteristics of the available capacity and discharge temperature rise of the battery when the ambient temperature and discharge rate are changed,the variation characteristics of the internal resistance of the battery when the ambient temperature,discharge rate and SOC are changed,and the variation characteristics of the entropy thermal coefficient of the battery when the SOC is changed.(2)Based on the modeling theory of battery heat generation and heat transfer,a threedimensional thermal model of a single battery was established,and the thermal simulation of the battery at different ambient temperatures and discharge rates was carried out,and the accuracy of the proposed model was verified by comparing the simulated temperature with the experimental temperature.Based on the simulation results,the surface temperature distribution characteristics of the battery under different discharging conditions were analyzed.(3)A liquid-cooling model of the battery module was established,and the effects of the coolant inlet and outlet positions,number and width of channels,outlet channel width and coolant mass flow rate on the cooling performance were studied by single-factor research method and multi-factor orthogonal experiment research method,respectively.The range analysis of the orthogonal experiment results was carried out to obtain the best combination of liquid cooling structural parameters.(4)The structure of liquid-cooling plate was redefined parametrically,and a liquid-cooling structure with increasing width channels was established.The optimal Latin hypercube experimental design method was used for sampling,and the accuracy of different types of surrogate models was compared,and a surrogate model for the liquid-cooling model of the lithium-ion battery module was established.The optimization problem of liquid-cooled structure was established,and the multi-objective optimization algorithm NSGA-II was used to obtain the optimal parameters of the liquid-cooling structure.