High Temperature Thermal Runaway Test And Simulation Study Of Ternary Lithium-ion Battery

Lithium-ion battery,especially high-nickel ternary lithium-ion battery,have become the best choice for electric vehicle energy sources due to their excellent overall performance.However,the frequent occurrence of electric vehicle safety accidents caused by the thermal runaway of lithium-ion battery has seriously hindered the commercial development of lithium-ion battery in the field of electric vehicles.Therefore,it is of great significance to conduct research on the thermal safety of lithium-ion batteries.This paper takes the high-nickel ternary material lithium ion battery?NCM811?provided by a battery manufacturer as the research object,and uses a combination of high-temperature thermal runaway experiment and simulation to study the lithium-ion battery under different working conditions?state of charge?SOC?=0,25%,50%,75%,and 100%?,the thermal characteristics shown when high temperature thermal runaway occurs,the work is as follows:Firstly,the structural composition,working principle,heat generation mechanis m and heat transfer mechanism of lithium-ion battery in normal working state were analyzed.At the same time,the occurrence mechanism,causes and main types of side effects of thermal runaway of lithium-ion battery were systematically studied.Secondly,the heat-wait-seek model of adiabatic accelerated calorimeter?ARC?was used to study the thermal characteristic parameters of lithium-ion batteries under five working conditions?SOC=0,25%,50%,75%and 100%?when the lithium-ion batteries experienced thermal runaway at high temperature.The experimental results show that:?1?the initial temperature of self-generated heat in the case of high temperature thermal runaway of lithium-ion battery is less affected by the SOC value of the battery and mainly affected by SEI decomposition;?2?the thermal runaway trigger temperature decreases with the increase of SOC value of the battery,and when the temper ature continues to be higher than 161?,the battery has the risk of thermal runaway;In the process of thermal runaway,the temperature of the drop of the voltage line and the damage of the safety valve decrease with the increase of the battery SOC;The hi gher the SOC value of the lithium ion battery is,the higher the maximum temperature reached in the process of thermal runaway is,the higher the maximum temperature rise rate is,and the more severe the damage degree of the battery is after thermal runaway.Finally,COMSOL Multiphysics software was used to establish a high-temperature thermal runaway model of lithium-ion battery,which simulated the process of high-temperature thermal runaway of lithium ion battery under four working conditions?SOC=25%,50%,75%and 100%?.The simulation results show that:?1?the temperature change curve in the simulation process of high temperature thermal runaway of lithium-ion battery is consistent with the experimental change curve,and the maximum simulation error of the highest temperature is only 6.9%,which verifies the accuracy of the model within a reasonable range.?2?during the simulation of thermal runaway at high temperature,the occurrence time of side reactions in the battery is earlier with the increase of the SOC value of the battery,which has the same rule as that in the test process,the trigger temperature of thermal runaway decreases with the increase of the SOC value of the battery.The minimum heat production in the simulation process of high temperature thermal runaway of the battery is 5E⁷W·m^-3,and the heat production of the battery increases with the increase of SOC,which has the same trend of change with the increase of SOC.?4?at the beginning of the lithium-ion battery thermal runaway,the temperature inside the battery will increase slowly,but when the battery internal side effects after began to generate heat,the battery temperature rise sharply,eventually trigger thermal runaway,and inside the battery positive electrode materials and electrolyte reaction heat production is far higher than other side reaction to produce heat,the anode materials and electrolyte reaction heat production is the main heat source in the process of thermal runaway.