Research On The Short Circuit Characteristics Of LiFePO₄ Batteries And Development Of Detection Early Warning Device

LiFePO₄ batteries have been put into a large number of use with the development of new energy vehicles.However,fire accidents caused by thermal runaway of LiFePO₄ batteries are constantly occurring.Short circuit is one of the important reasons to trigger the thermal runaway of the battery.When the LiFePO₄battery is short circuited,a large short circuit current will be generated instantly,and it will accumulate a large amount of heat in a short time,which is likely to cause irreversible damage to the battery and cause fire hazard of thermal runaway.Therefore,it has great theoretical and practical significance to research the characteristics of battery short circuit and develop an early warning device that can identify and judge battery short circuit.The research object of this paper is 32650 LiFePO₄ batterry which can be used in new energy vehicles.The internal short circuit experiment scheme and external short circuit experiment scheme are designed and the experimental platform of nail penetration internal short circuit and external short circuit for LiFePO₄ batteries is built respectively refer to Chinese national standard testing requirements.On this basis,a large number of experimental studies on internal short circuit and external short circuit of LiFePO₄ batteries are carried out,and the battery voltage,short circuit current,surface temperature and video data of LiFePO₄ batteries in the case of short circuit are obtained.Several findings are found through the experimental results and data analysis of the internal short circuit and external short circuit of a large number of LiFePO₄batteries.When the nail penetration internal short circuit occurred in LiFePO₄batteries,intensity of thermal runaway about cylindrical LiFePO₄ batteries caused by nail penetration is random.The battery voltage would drop to 0 V after battery penetrated,and will drop more rapidly if the battery sprays smoke and explodes.The temperature of the battery will rise rapidly after nail penetration,and it will rise faster and higher as the battery belches smoke or explodes.When the external short circuit occurred in LiFePO₄ batteries,the electrical characteristics of the battery could be divided into three periods during the external short circuit process,including the first period of stable battery voltage with high short circuit current,the second period of voltage with a rapid current drop,and the third period,i.e.,batteries are damaged.The maximum cell surface temperature increases linearly with the initial temperature and the initial state-of-charges?SOCs?.The rise rate of battery surface temperature decreases with the increase of initial temperature and initial SOCs.Taking battery voltage,short circuit current and battery surface temperature as parameters for detection.A set of detecting and warning device for short circuit safety state of LiFePO₄ batteries with functions of parameter detection and short circuit safety state display is developed.Based on the short circuit test results and further data analysis,a short circuit warning algorithm for LiFePO₄ batteries is designed.After the short circuit warning algorithm of LiFePO₄ batteries is implanted into the detection and warning device,the function verification experiment of the detection and warning device is carried out.The experimental results show that the device,which can realize the detection and warning of various short circuit conditions of LiFePO₄ batteries.