Study Of The Thermal Safety Of Typical Combustible Components In Lithium Ion Batteries

With the priorities of outstanding storage characteristic,relative long service life,friendly to the environment,lithium-ion batteries(LIBs)have been applied in every walk of life after many years development.Therefore,carrying out the investigation on LIBs fire hazard not only enhances the comprehension of the LIBs fire mechanism,but also provides theoretical basis for designing LIBs with higher safety.As for the most important parts in LIBs such as electrode materials,electrolyte and separator,the majority of heat is generated from their combustion process.However,because of the various and complicated physical and chemical changes in the combustion reactions,it is hard to understand the influence of each part in LIBs fire.Thus,in order to analyze the role of each part in LIBs fire,the LIBs were divided in this work.The main research contents are as following,The fire hazard of electrolyte and the effect of low-pressure atmosphere were investigated.Cone calorimeter was used to test the electrolyte with different ratio carbonates or lithium salts.According to the previous research about the traditional and classical thermal chemistry(TC)technique,the heat release rate(HRR)is calculated.Combined with the data of Thermogravimetry-Fourier Transform Infrared Spectroscopy(TG-FTIR),the applicability of TC method and oxygen consumption(OC)calorimetry.TC technique was not applicable when the generation of amount carbon dioxide was not from the combustion of electrolyte,while the OC calorimetry was quite accurate.Under the low-pressure environment in Tibet and Yunan,the influence of atmospheric pressure to mass loss rate(MLR)and HRR was investigated.There was a positive exponential relationship among the average and peak values of MLR with the pressure during the steady combustion process of the electrolyte pool fire,which meets the accordance from previous research results about the change rules of hydride exponential coefficient.The average HRR of LiBF4 electrolyte was a little higher than that of LiPF6 under low altitude condition,while the average HRR of LiBF4 was significantly lower than that of LiPF6 under low-pressure environment.Since the molecular weight of LiBF4 is lower,so the total HRR of LiBF4 was higher.Hence,the addition of LiBF4 could not improve the safety of electrolyte.The reactivity between charged positive electrodes of(NMC)and traditional carbonate-based electrolyte with or without different electrolyte additives at elevated temperatures was methodically investigated using accelerating rate calorimetry(ARC).The ARC results illustrate that the upper cut-off potential and sample morphology,influence the thermal stability of NMC materials,while additives and coatings have a smaller effect.Some outcomes of the work are that the high content of Ni would significantly make the cells become more reactive.The effects of temperatures,catalysts,and catalyst contents on polyethylene(PE)pyrolysis were investigated by using single-photon ionization time-of-flight mass spectrometry(SPI-TOFMS).The mass spectra of pyrolyzed PE and PE/catalysts from 300? to 800 ? illustrate that the pyrolysis reactions were apparently promoted and varied by introducing HZSM-5,HUSY,and MCM-41.As microporous catalysts,HZSM-5 and HUSY were found to accelerate the BTX formation at 400 ?,which could not be observed for pure PE until 800 ?.With the existence of MCM-41,only alkenes were produced below 600 ?.The pyrolysis processes could to be accelerated by adding catalysts.Principal components analysis(PCA)was finally employed to identify the main factors with influence on the products distribution.Analytical results showed that the yield of the majority of products could be affected by different experimental conditions,that the type of catalysts makes the most significant influence.The impact of different types of catalysts on fire hazard of PE was studied by using the cone calorimeter.The results indicated that the time to ignition(TTI)and the peak HRR were changed remarkably.It is worth noting that with the addition of MCM-41,the pHRR is the minimum.