Fire Risk Evaluation of the Internal Components of the Li-ion Batteries

Abstract

The advantages of Lithium-ion batteries (LIBs) are well known, anyway the LIBs are even considered hazardous products. In fact, outside the safety windows the Li-ion cells can undergo to an abuse that leads to the degradation of the internal components with the release of gases, vapour, and solid products. The reactivity of the LIBs and the relative products composition is strictly correlated to the chemical composition of the internal components. Because of a lack of regulation, safety data sheets (SDSs) of Li-ion cells are not mandatory but, generally they are available. However, there is a gap between the information reported in the SDS and the internal chemical composition, and usually the quantity of components is expressed as a range of weight percentages, and the chemical composition is not well specified. The most common lack of information concerns the electrolyte, which is usually defined as a mixture of organic carbonates without reporting the type of solvents (e.g., dimethyl carbonate, diethyl carbonate, and ethylene carbonate), the ratio between these components, and possible additives. The aim of this work was to characterize the internal components of various cylindrical 18650 cells available on the market, i.e., cell with Lithium Nickel Cobalt Aluminium Oxide (NCA) as cathode and graphite (C) or Lithium Titanate Oxide (LTO) as anode, and cells with Lithium Iron Phosphate (LFP) as cathode and C as anode. For this purpose, the cells were disassembled in a glovebox filled with argon (O2 and H2O = 0.1 ppm) and then the different components were analysed by various techniques to define their chemical composition, i.e., metals of the electrodes by ICP-OES, the electrolyte by GC-FID and SPME-GC-MS, and the separator by ATR-FT-IR and DSC. The identification of those compounds is fundamental to understand the reactions occurring inside the cells and to evaluate the risks for human health and environment.