Rapid operando gas monitor for commercial lithium ion batteries: Gas evolution and relation with electrode materials

Internal gases caused by side reactions are crucial signals for evaluating health and safety states of Li-ion batteries (LIBs) while it is still a great challenge to timely realize accurate monitoring. To address the issues of implanting various gas sensors into commercial batteries, here a novel method is developed to fast operando monitoring gas evolution via equipping non-dispersive infrared multi-gases sensors into a sealed tank, where real commercial batteries with one open end could be settled for operating. The generated CO2 concentration is strongly linked with both voltage and temperature, while the concentrations of CH4 and C2H4 are solely dependent on temperature. As a typical trace gas, evolution behaviors of CO2 have been related to O2 generation from LiNi0.5Mn0.3Co0.2O2 positive electrode, implying stable CO2 release below a critical voltage of 4.5 V. By tracking CO2 concentration, an increased amount of Li2CO3 was monitored on the surface of graphite negative electrode during discharge process at different temperatures and cutoff voltages, which contributes to the component variation of solid electrolyte interfaces. Such operando techniques promise a platform for well understanding the interaction of side reactions linked with gas evolution between positive and negative electrodes in commercial LIBs.