| Currently,the range,charging speed,and driving safety are still the three core pain points hindering the promotion and popularization of new energy electric vehicles,and the emergence of fast charging technology can effectively solve the problem of charging speed.However,the self heating generated during the charging/discharging process seriously hinders the performance,stability,and safety of fast charging batteries.If the temperature of a certain battery exceeds the normal operating temperature,it is extremely prone to heat runaway,and even spread to the entire battery pack,leading to a vehicle fire and explosion.Therefore,it is of great significance to design an effective battery thermal management system that can meet the requirements of high rate charging and discharging heat dissipation and inhibit uncontrolled heat transmission.Firstly,this paper describes the composition,structure and working principle of lithium ion battery,deeply understands the mechanism of heat generation and thermal runaway of lithium ion battery,introduces the basic principle of heat pipe and related theories of fluid mechanics in detail,which provides a theoretical basis for the research on heat dissipation and thermal resistance isolation of power lithium ion battery liquid cooling system.This article takes a 50 Ah square ternary lithium-ion battery as the research object,constructs an electrochemical thermal coupling model for lithium-ion batteries,and conducts experimental research.The correctness of the model is verified by comparing the output voltage and temperature rise data obtained from numerical simulation of the battery with experimental results.Based on this model,calculate the heat generation of ternary lithium-ion batteries at different discharge rates.Secondly,on the basis of obtaining the heat generation of ternary lithium-ion battery cells,this article proposes a liquid cooling system scheme based on a "sandwich" composite plate composed of "flat heat pipe insulation plate flat heat pipe" to address the problem of pure liquid cooling systems being unable to carry away the heat generated by high rate charging and discharging.The corresponding power lithium-ion battery pack model is established,taking into account the impact of the composite plate on the energy density of the battery pack,And the influence of different numbers and thicknesses of composite plates on the heat dissipation performance of the battery module was studied.Through comparison,the scheme of selecting 5mm thick composite plates and 13 composite plates for the battery pack model.Based on this scheme,the effects of discharge rate,coolant inlet flow rate,and temperature on the temperature of the battery pack were studied under three working conditions.The results showed that the power lithium-ion battery liquid cooling system coupled with flat heat pipes can meet the heat dissipation requirements of high rate charging and discharging.Finally,a single cell thermal runaway model was established for the thermal runaway condition of the battery and its correctness was verified.A thermal runaway propagation model for battery modules was established based on the thermal runaway of individual batteries.The influence of a composite plate liquid cooling system composed of a "flat heat pipe insulation board flat heat pipe" on the thermal insulation performance of battery modules was analyzed,and the effects of different thermal resistance and cooling capacity of insulation boards on the thermal insulation performance of battery modules were studied.In summary,the liquid cooling system based on this composite plate can effectively reduce the risk level caused by thermal runaway,and has important practical significance for improving the safety performance of electric vehicle power batteries. |
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