Experimental evaluation of thermolysis-driven gas emissions from LiPF 6-carbonate electrolyte used in lithium -ion batteries

This paper performs an experimental evaluation of thermolysis-driven gases generated by the thermal decomposition of 1 M LiPF6+EC/DMC=1:1 v:v electrolytes at various decomposition temperatures, pyrolysis durations, and oxygen concentrations. Carried out in a home-built autoclave filled with pure helium, the experiment reveals that as the decomposition temperature increases, more types and larger quantities of gases will be released. Specifically, the experimental results demonstrate trends of logistic growth in the volume concentration of CO2, C2H6O, C2H4, CO, and C2H4O2 with the increase of decomposition temperature. With a prolonged pyrolysis duration, while volume concentrations of certain gases, such as CO2, C2H6O, C2H5F, and CO would increase, the concentration of C2H4O2 actually decreases. Moreover, concentrations of both C2H4 and C2H5F will first decrease and reach their minimum values at 1% v/v oxygen concentration, and then they would quickly climb back at higher oxygen concentrations, while the concentrations of C2H6 and C2H3F would decrease monotonically. It is envisioned that the detailed experimental results and findings on the gas generation pattern of 1 M LiPF6+EC/DMC=1:1 v:v electrolytes can facilitate the development of an early warning mechanism of thermal runaway based on gas sensing technology, which can be effectively applied to monitor the potential thermal failures of lithium-ion batteries with the same type of electrolyte and thus promote the thermal safety of battery packs in safety-critical applications. © 2020