Study On Online Detection Method Of Thermal Runaway Gas In Lithium-ion Batteries Based On Raman Spectroscopy

Lithium-ion batteries are widely used in various fields due to their high energy density,high environmental protection and high cycle life.However,lithium-ion batteries in the long-term charge and discharge cycle due to lithium dendrites,mechanical abuse and other objective incentives,may trigger thermal runaway and produce a large number of toxic or highly flammable gases,resulting in subsequent severe fire or explosion.Therefore,real-time analysis of thermal runaway gases is of great significance for early warning,safety assessment and safety management of lithium-ion battery thermal runaway.In view of the above challenges,this paper develops an in-situ online gas detection method for the whole process of thermal runaway of lithium ion batteries based on gas Raman spectroscopy,and captures the key gas markers in real time to accurately analyze the dynamic evolution mechanism of thermal runaway.This paper mainly carried out the following three aspects of research:1.A highly sensitive Raman gas analysis system was set up for battery thermal abuse and uncontrolled environment.In this paper,the optimal experimental parameters of Raman gas analysis system were determined,and the gas components released during thermal runaway were captured in real time.It was revealed from the data that the main gas components released during thermal runaway of the battery were CO₂,CO,H₂,CH₄,C₂H₄,C₃H₆and electrolyte solvents.,and the chemometric models of each component were constructed respectively.The results show that the gas Raman spectroscopy technology can perform multi-component analysis on the thermal runaway gas of lithium-ion battery in the second-order time,which becomes a powerful tool for studying the thermal runaway mechanism.2.The real-time release characteristics of thermal runaway gas in NCA lithium-ion battery were studied by gas Raman spectroscopy,and the influence of SOC and confined space size on the safety of pyrolysis gas in lithium-ion battery was revealed.The results show that the smaller the confined space is and the higher the SOC is,the more the total gas released by the battery is,and the wider the explosion limit is,showing higher explosion risk and lower combustion efficiency.In addition,according to the curves of battery voltage and temperature,the whole thermal runaway process is further divided into five stages.The abnormal trend of the maximum gas temperature first decreases and then increases with the increase of battery SOC is analyzed,and the influence of battery SOC and confined space on17 key parameters of heat abuse events is discussed.The results show that the smaller the limited space and the higher the SOC,the lower the thermal stability of the battery,the more intense the thermal runaway,the earlier the thermal runaway characteristic fault signal occurs,and the less the emergency treatment time.3.The batteries with LCO,NCM111 and NCM811 as cathode materials under different SOCs were selected as the research objects,and the thermal safety of NCM811 batteries was compared and analyzed.A new gas detection method coupled with GC-MS and Raman spectroscopy was proposed to reveal the dynamic changes of the detailed components of the released gas,the main components of the released gas and the limit risk of gas explosion at critical moments in the thermal abuse of the battery.The results show that the influence of SOC on the thermal safety of different batteries presents a consistent law,that is,the higher the SOC is,the worse the thermal stability of the battery is and the more severe the thermal runaway is.The more the released gas amount and gas type are,the higher the gas risk is.At the same time,the release amount of CO₂,CO,H₂,CH₄,C₂H₄and C₃H₆increases with the increase of SOC.The thermal runaway gas of high SCO battery shows more dangerous toxicity and flammability.Compared with LCO battery and NCM111 battery,NMC811battery has worse thermal stability,more severe thermal runaway and more gas released.The maximum overpressure and gas released by 100%SOC NMC811 battery are 452.2 k Pa and5.59 L,respectively.The gas amount and explosion limit range of CO₂,CO,H₂and CH₄generated by thermal runaway of NCM811 battery are significantly higher than those of the other two batteries.The maximum explosion limit of the gas released by NCM811 battery reached 76.93%.CO,CO₂and C₃H₆O₃gases appeared in the early stage of thermal abuse of the three kinds of batteries,and the reaction mechanism was further explained comprehensively according to the composition of thermal runaway gas detected by GC-MS.The gas concentrations of LCO,NCM111 and NCM811 cathode materials reached the explosion limit at about 49 s,45.5 s and 28 s after the opening of the safety valve,respectively.