Experimental Study Of Electrolytes Of Lithium Ion Batteries By Cone Calorimeter

We have been dependent on fossil fuels so much that a series of problems arise along with it, and the overuse of traditional energy can lead to its depletion. As a kind of new energy, lithium ion battery is getting more and more attention worldwide due to its excellent performance such as the high energy density, long life cycle, less pollution environmentally, and so on. However, the safety problem of lithium ion batteries has become a universal handicap that impedes its popularization worldwide. Fire and explosion accidents caused by thermal runaway of lithium ion battery have been reported commonly. Therefore, studies on thermal safety and fire hazards of lithium ion batteries can help understand the basic rules of lithium ion battery thermal runaway and the related fire phenomenon, quantify the fire risk of lithium ion batteries, and decrease personal injury and property damage consequentlyA lithium ion cell is generally composed of the positive and negative electrodes, electrolyte and the separator. Most of the electrolyte components inside a lithium ion cell are flammable organic liquids. When a lithium ion cell undergoes thermal runaway, the decomposition of electrode materials and the electrolytes can generate amounts of gases, leading to the overpressure inside a battery and ejection of various gases and electrolyte liquids, which can trigger fire or explosion accidents finally. Thus the electrolyte is considered as the key component of fire hazard of a lithium ion battery system. Research on the electrolyte of lithium ion batteries has been an active area recently. The most commonly electrolyte used in a lithium-ion cell is typically a mixture of organic carbonates with a salt called lithium hexafluorophosphate dissolved in it. Researchers at home and abroad have conducted lots of research on the electrolytes of lithium ion batteries, but their focuses are mainly put on the decomposition reactions of the electrodes and electrolyte or the electrolyte itself, obtaining better battery performances by seeking for new functional additives or by developing new nonorganic solvents, understanding the thermal behavior characteristics by testing various electrolyte samples, and so on. Indeed, many valuable conclusions have been drawn. However, studies on the fire behavior and combustion properties of lithium ion battery electrolytes have rarely been targeted.Based on the analysis above, some of the combustion properties of three carbonate solvent mixtures commonly used as the electrolytes of lithium ion batteries are considered by means of the ISO5660-1cone calorimeter in this paper. Some key parameters governing the fire-induced hazards such as the heat release rate (HRR), total heat release (THR), mass loss rate (MLR), combustion efficiency, and the concentration of the major exhaust gases are determined and analyzed. Experimental findings reveal that the heat release rate, the most important parameter in fire science, exhibits a significant variation among the carbonate mixtures. Furthermore, as some researchers argue that oxygen consumption calorimetry is likely to over-predict the chemical heat release for lithium ion cells, another thermal chemistry method based on stoichiometry for heat release rate calculation is adopted to validate the effectiveness of the oxygen consumption calorimetry. Heat release rate results of the three carbonate solvent mixtures obtained by these two separate methods are found to be in good agreement. Thus, oxygen consumption calorimetry is considered to be an appropriate technique to determine the heat release in fires in relation to electrolytes of lithium ion batteries.