Experimental Study On Thermal Runaway Characteristics Of Large Capacity NCM Lithium-ion Batteries Under The Electrothermic Interaction

In recent years,thermal runaway(TR)of lithium-ion batteries has led to frequent fire accidents in electric vehicles,and their safety issues urgently need to be addressed.In reality,the triggering of TR in lithium-ion batteries is often influenced by multiple external abuses.A common scenario is the electrothermal interaction during the charging process,including two situations:the combined action of electric and thermal abuse,and the combined action of normal charging and thermal abuse.Compared to single abuse,there are certain differences in the characteristics and mechanisms of TR under electrothermal interaction.Most of the previous research on battery thermal safety has focused on the TR under single abuse,and a small number of studies on TR under electrothermal interaction mostly use numerical simulation or only conduct small battery experiments,lacking more dangerous physical experiments on large batteries.Therefore,further experimental research is needed on the TR characteristics of NCM lithium-ion batteries with wider applications and larger capacity under the electrothermal interaction.This article takes a 50 Ah high capacity NCM lithium-ion battery as the research object,and uses the TR time as the combination standard of electrothermal interaction conditions.Using a high-power charging and discharging cycler and an electric heating plate,experiments were conducted on the TR behavior of the battery under the overcharging,overheating,combined effects of overcharging and overheating,as well as under the combined effects of normal charging and overheating.The characteristics of the TR behavior,thermal parameters,and electrical parameters of the battery in different scenarios were analyzed in detail,A risk assessment method for TR under different abuse and a mechanism for the electrothermal interaction have been proposed.The main conclusions of this article are as follows:(1)Under the combined action of overcharging and overheating,the TR time of the battery is short,the surface temperature is high,the TR SOC and mass loss are relatively large.Compared to 1 C overcharging and 150 W overheating,the TR time under their combined action is shortened by more than 34%.The maximum average temperature and maximum temperature rise rate of the battery surface exceed 3.5 times that of overcharging,and the TR SOC and mass loss increase by 27%and 18%respectively compared to overheating,During the process of TR,the voltage shows a trend of "continuous increase-sudden drop to zero",and the mechanism of TR is more similar to overheating rather than overcharging.(2)When the overheat factor dominates the electrothermal interaction,the TR is close to overheating in external characteristics and mechanism.When the overcharge factor dominates,the TR is closer to overcharge as the battery SOC increases.The severity of battery thermal runaway is determined by the thermal runaway SOC,rather than the abuse method.The risk of TR of batteries under electric-heating abuse can be comprehensively evaluated by the probability and consequences of TR mainly affected by overheating and overcharging respectively.(3)Under the combined action of normal charging and thermal abuse,the higher the initial SOC of the battery,the greater the charging rate,and the faster and more intense the TR;When the battery in a low SOC,TR will occur during charging,and the voltage before TR will suddenly increase to more than 10 V.Under the conditions studied in this article,the TR time of 75%TR SOC batteries is shortened by more than 19%compared to thermal abuse,and the TR trigger temperature is reduced by nearly 10℃.When the battery in a high SOC,the TR under combined action is similar to that under thermal abuse.The mechanisms for accelerating TR due to the combined effects of normal charging and thermal abuse include reducing the triggering temperature of TR and increasing the temperature rise rate of the battery.This article can provide a reference for the further improvement of thermal safety management strategies for existing automotive power lithium-ion batteries.