Study On Phase-change Heat Transfer Of Low Temperature Lithium Ion Power Battery

Aimed at alleviating the energy shortage and environmental con cerns,electric vehicles(EVs)industry has been booming recently.Lithium-ion batteries(LIBs)are commonly used as power batteries for EVs because of their low self-discharge rate,high energy density and long worktime.However,the working performance and safety of LIBs are extremely influenced by temperature condition.To ensure the operating performance of LIBs,researchers have conducted studies on the battery thermal management(BTM)of LIBs.However,most of the theoretical and experimental studies focused on the heat dissipation performance of LIBs.However,LIBs in cold climate are faced with the problems of significant capacity attenuation and outstanding safety risks.Therefore,it is very necessary to carry out researches on BTM of LIBs in cold climate.In this paper,theoretical analysis and numerical simulation are conducted to study the preheating and heat preservation strategies of 18650 LIBs in cold climate.The main work and innovation points are as follows:(1)A mathematical model of the cell was established.The temperature rise of the cell was numerically studied,and the reliability of the numerical method was verified by test data.And the mathematical model of battery pack was established.The temperature rise of battery pack when discharge under different low temperature conditions was numerically analyzed.The deficiencies of BTM of a single heating plate and the single Phase Change Material(PCM)were explored,and strategy of coupling heating plate and PCM was proposed.A preliminar y structure was proposed,and the coupled BTM performance at different low temperatures was studied.(2)The battery pack model with different structure was established,analyzed four kinds of heating plate arrangement under different temperature conditions and the influence of PCM coupled BTM,and chose the best arrangement to further study the cell spacing,types of PCMs and composite phase change materials under low temperature environment the influence of thermal performance of the cell.(3)The battery pack with insulation layer was built.The influence of three types of materials and their thickness on the BTM performance of LIBs in cold environment were investigated.Finally,a dimensionless parameter of energy compensation is introduced to evaluate the efficiency of BTM of the battery in cold environment.Finally,a dimensionless parameter of energy compensation is introduced to evaluate the efficiency of BTM in this paper.The evaluation index shows that the optimal preheating and insulation strategy has a good energy compensation ratio.