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 LiNi_0.5Mn_0.3Co_0.2O₂ 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.