Abstract
In recent years, lithium-ion batteries (LIB) have advanced in performance and capacity, and their applications to electric vehicles, next-generation mobility, mobile devices, etc. are expanding. However, LIB may be ignited or exploded due to external stimuli such as short circuit, impact, heating, etc., and the number of accidents of ignition or explosion is increasing with the expansion of these applications and the increase of energy density.
In this study, we investigate the case where the external environmental temperature of LIB rises, and the reaction runaway occurs. As an item of safety evaluation, the purpose is to establish a method for measuring the temperature rise and pressure rise of a battery and evaluating the amount of reaction product gas and the gas composition. If the amount of gas generated is known in advance, it can be used for studying protective measures and designing closed containers for safety tests.
In the experiment, the 20L closed chamber used for the explosive experiment was modified and used for LIB experiment. A LIB with electric heater were introduced into the explosion chamber and the behavior of runaway reaction was observed, monitoring the terminal voltage, internal pressure, and temperature. Further, after the test, the gas was sampled, and the amount of gas was estimated and the gas composition was analyzed. We also compared the results of two LIBs with SOC (State of Charge) of 0% and 95%.
As a result, the following findings were obtained. (1) An experimental system was developed to evaluate the amount of the gas without leakage causing the thermal runaway while monitoring the LIB temperature, voltage, and pressure inside the container. (2) It was found that the LIB temperature reached ~ 1200 ° C (SOC 95%) and ~ 600 ° C (SOC 0%) during the runaway reaction. (3) The amount of gas during the runaway reaction is 141 to 152L (SOC 95%), 72L (SOC 0%), and special attention should be paid to the gas generation when the LIB is charged completely. (4) The gas after the runaway reaction contains about 30% carbon monoxide, 15% hydrogen, 26% hydrocarbon (SOC 0%), 50% (SOC 0%). We should pay attention to the CO poisoning, backdraft, and flash.
Figure 1