【Abstract】 The research on the heating characteristics of lithium-ion batteries is of great significance to the development of battery thermal management systems. This paper uses numerical methods to study the micro-heating characteristics of lithium batteries during discharge, and the solid electrolyte (SEI) ) Film and ohmic heat change law was analyzed, the research results show that: when the lithium battery pack
is discharged at a high rate (u003e5C), the heat generated by the SEI film is an important part of the heating of the lithium battery; as the discharge cycle progresses, the lithium battery The SEI film on the surface of the negative electrode particles thickens linearly, which leads to the continuous increase of the battery SEI film resistance; the higher the lithium battery discharge environment temperature, the faster the lithium battery negative SEI film thickens and the faster the capacity decline. [Keywords] ; Thermal management; Discharge cycle; Capacity decline; Solid electrolyte membrane; 0 Introduction has the advantages of higher specific energy, discharge voltage and better cycle life, and is considered as a pure electric vehicle (EV) and one of the best energy storage devices for hybrid electric vehicles (HEV). The thermal management system is one of the core technologies to ensure the safe operation of high-power lithium battery packs. Too high temperature will cause damage to the surface electrolyte (SEI) membrane of the lithium battery, thereby shortening the battery cycle life, and may cause safety issues such as battery explosion. Therefore, studying the thermal characteristics of lithium batteries under complex operating conditions is the basis for the development of battery thermal control technology, and has important scientific guiding significance for the development of power battery thermal management systems. At present, the research on the heating characteristics of lithium batteries mainly adopts numerical simulation and experimental analysis. Based on the electrochemical model proposed by Doyle and the electric quantity equation proposed by Bernardi, scholars at home and abroad have developed a number of thermoelectric coupling models for lithium batteries. For example, the thermoelectric coupling model is used to calculate the discharge characteristics of lithium batteries at different temperatures. And analyzed the influence of temperature-related parameters on the discharge characteristics of lithium batteries. And the thermoelectric coupling model is used to calculate the temperature of the wound lithium battery pack, and the calorific value of different heat sources inside it is analyzed in detail. J. Vazquez-arenas et al. used a thermoelectric coupling model to simulate a square lithium-ion battery, studied the influence of battery temperature on its discharge characteristics and lithium ion concentration distribution, and quantitatively analyzed the calorific value of different heat sources inside the battery. At present, most literatures on the thermal characteristics of lithium batteries adopt thermoelectric coupling models, but the problem of capacity degradation of lithium batteries is rarely considered. During the charge-discharge cycle of a lithium battery, the negative electrode film will gradually thicken due to the deposition, which will increase the internal resistance of the lithium battery, which will cause a significant increase in the heating rate of the lithium battery pack. In the thermoelectric coupling model of the lithium battery, the cycle decay problem is considered, and the influence of temperature on the capacity decay of the lithium battery is analyzed. However, the capacity decay process of the lithium battery adopts a function fitted from experimental data. The established model and research results are only The specific lithium battery suitable for its research lacks versatility. Et al. proposed a thermoelectric coupling model including the capacity decline process of lithium batteries, but the dissolution of the positive active material used in them is only obvious in lithium manganese batteries, and is not suitable for lithium cobalt oxide and lithium iron batteries. The characteristics of heat change during battery cycling. This article will consider the discharge characteristics, heat characteristics and decay process of lithium batteries at the same time during the cycle, and conduct a numerical study on the heat composition and heat change characteristics of lithium batteries during the charge and discharge cycle. u003cpu003e In the application of this article, the thermoelectric model of the battery is used, and the influence of the change of the SEI film during the battery cycle decline on the heat generated by the battery is considered, and the heat change of the lithium battery during the cycle and the temperature on the life of the lithium battery are analyzed in detail The following conclusions are drawn: 1. During the high-rate (u003e5C) discharge process of lithium batteries, the heat generated by the SEI film is an important part of the heat generated by the lithium battery, accounting for more than 14% of the total heat; 2 , With the progress of the discharge cycle, the SEI film of the negative electrode of the lithium battery pack will gradually thicken, and the higher the discharge environment temperature, the faster the growth of the SEI film and the faster the capacity decline;u003c/pu003eu003cpu003e3, the thickness of the SEI film and The resistance increases approximately linearly with the increase of the number of discharge cycles;u003c/pu003eu003cpu003e4. The heat and temperature rise generated by the SEI film during the discharge of the lithium battery will gradually increase with the increase of the number of discharge cycles. u003c/pu003eu003c/pu003e
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