| Lithium-ion batteries are widely used for their high energy density,green and environmental advantages.The frequent accidents of new energy vehicles in recent years have seriously affected the promotion and use of new energy vehicles.One of the main reasons for the thermal runaway of Li-ion batteries is that the heat generated cannot be diffused outwards in time,resulting in the continuous accumulation of heat,so it is important to study the thermal diffusion of Li-ion batteries.The convective heat transfer coefficient is one of the important thermal parameters,which plays a decisive role in the heat dissipation of lithium batteries.In order to study the distribution of heat dissipation in lithium batteries more accurately,the convective heat transfer coefficient is calculated for each temperature at different flow rates based on the calculation method of the average surface heat transfer coefficient of the fluid swept down tube bundle in heat transfer theory.The effect of the convective heat transfer coefficient on the temperature field of lithium batteries under different heat generation and dissipation conditions and its extent are investigated.The structural composition and heat generation principle of Li-ion batteries are analyzed,and the heat generation principle and types of side reactions when thermal runaway occurs in Li-ion batteries are also analyzed,providing a theoretical basis for Liion battery simulation and model research.Taking 18650 ternary lithium battery as the research object,an air-cooled heat dissipation model coupled with the total model,heat transfer model and fluid flow model is established to simulate and analyse the effect of convective heat transfer coefficient on the temperature field of lithium battery during normal operation when temperature effects are considered.The results of the study show that the convective heat transfer coefficient affects the temperature field of the lithium battery to different degrees when the temperature effect is considered.When the air flow rate is 0.05,0.2,0.3 and 0.5m/s respectively,the temperature function of the lithium battery causes the temperature difference during the discharge of the lithium battery to change by less than 1%,but when the air flow rate is 0.1m/s,the temperature field of the convective heat transfer coefficient considering the temperature effect when the lithium battery is discharged to 729 s decreases by 21.71% compared to the temperature field at a constant.A thermal runaway model for Li-ion batteries was developed to study the effect of convective heat transfer coefficient on the temperature field of Li-ion batteries during thermal runaway considering the temperature effect,and to analyze the main sources of internal heat generation in Li-ion batteries during thermal runaway.In the Li-ion battery thermal runaway simulation,the effect of temperature on the convective heat transfer coefficient is higher than 3%,and the analysis of the simulation results shows that in the thermal runaway model,the convective heat transfer coefficient has an effect on the temperature field of Li-ion battery when the temperature effect is considered,and in the high temperature thermal runaway model,the temperature field when the convective heat transfer coefficient considers the temperature effect is reduced by 2.22% at 1267 s compared with that when the convective heat transfer coefficient is constant;in the pinning thermal In the overcharge thermal runaway model,the temperature field of the convective heat transfer coefficient considering the temperature effect is reduced by 8.99%at 509 s compared with the constant convective heat transfer coefficient;in the overcharge thermal runaway model,the temperature field of the convective heat transfer coefficient considering the temperature effect is reduced by 16.11% at 3395 s compared with the constant convective heat transfer coefficient,and the main heat sources of the lithium battery thermal runaway are the reaction between the negative electrode and the electrolyte The main sources of thermal runaway in Li-ion batteries are the reaction between the negative electrode and electrolyte and the decomposition of the positive electrode.Finally,a water-cooled heat dissipation model for lithium batteries was established to study the effect of convective heat transfer coefficient on the temperature field of lithium batteries during water-cooled heat dissipation considering the temperature effect.In the water-cooled heat dissipation model,the flow channel uses a rectangular structure,and the contact area between the flow channel and the lithium battery is small,so the convective heat transfer coefficient changes less than 5% between 30 and 40°C.Therefore,when the water-cooled flow velocity is 0.05 and 0.1m/s respectively,if the flow channel is designed to have a small contact area with the lithium battery,the convective heat transfer coefficient considering the temperature effect makes the lithium battery temperature field change less than 1%,but in the lithium battery In the simulation of high temperature thermal runaway of Li-ion battery,the temperature field of convective heat transfer coefficient when considering the temperature effect is 66°C lower than when the convective heat transfer coefficient is constant when the water cooling flow rate is 0.1m/s.Therefore,the effect of temperature on the convective heat transfer coefficient cannot be ignored when simulating and studying the effect of water cooling heat dissipation on high temperature thermal runaway of Li-ion battery.Figure [45] Table [6] Reference [84]... |
