Study On The Safety Of Lithium Titanate Battery Overcharge For Rail Transit

In recent years,with the increasing use of lithium titanate batteries in rail transit equipment,people have paid more and more attention to the safety of lithium titanate batteries.Although it is generally believed that the safety of lithium titanate is high,its safety performance is mainly concentrated in the two aspects of lithium that is not easy to analyze and its internal structure changes will inhibit the passage of large currents after the occurrence of internal short circuit,but there is little research on the safety of overcharging,which is a very dangerous electrical abuse method.Therefore,taking the different types of overcharge faults of lithium titanate batteries used for rail transit as the background of research,cyclic overcharge experiments under different SOCs and overcharge to thermal runaway experiments under different conditions were carried out,and the main contents and results of the experiments were as follows:(1)The thermal runaway behavior of lithium titanate under the 1C charging rate was carried out to achieve a preliminary grasp of the thermal runaway behavior of lithium titanate under the 1C charging rate,and the thermal runaway process was divided into four stages according to the key nodes of the battery voltage and surface temperature change in the overcharge process,and the characteristics of the voltage and temperature changes at each stage and the types of side reactions that may occur were summarized and the main reasons for the changes were explained;(2)In view of the cyclic overcharge fault that may occur in the actual application process of lithium titanate batteries,this paper conducts cyclic overcharge experiments under different SOCs,simulates the cyclic overcharge scenarios in the three stages before thermal runaway occurs,and summarizes the impact on battery internal resistance and capacity change.In this paper,the IC curve is also used to analyze the decline pattern caused by different degrees of overcharge,and the experimental phenomenon shows that the LAM type decline dominates the two stages of lithium titanate overcharge I.and II.,and the position of the peak moves to the low voltage region after the beginning of phase III at the end of phase II.In addition,the main side reactions that occur in the early stage of lithium titanate batteries after overcharging are also speculated,and the identification and evaluation of overcharged lithium titanate batteries based on special changes at the end of the high voltage section of the IC curve are realized;(3)For the extreme situation that lithium titanate batteries may run out of heat during overcharge,this paper designs overcharge thermal runaway experiments under different conditions,explores the charging rate,battery capacity size,battery packaging form and other three influencing factors that affect the thermal runaway behavior of lithium titanate batteries,and summarizes the relevant laws.In addition,the key data such as the maximum temperature on the surface of the battery,the maximum temperature rise rate,the thermal runaway trigger time,the duration of the open flame,and the duration of the jet fire are summarized in this paper,and a safety evaluation method for lithium titanate battery overcharge thermal runaway is constructed by using the analytic hierarchy method.