Detection of First Venting in Battery Failures with Carbon Dioxide Sensors

Abstract

Li-ion battery thermal runaway is a critical safety issue for large-scale battery packs. Upon battery failure, gas venting can occur when the cell's internal pressure exceeds a critical value and causes cell rupture and electrolyte leakage. The gas venting is usually categorized into first venting events and thermal runaway gas venting events (second venting). The first venting occurs around 120 °C and can be considered as a precursor to thermal runaway. The subsequent venting during thermal runaway is more aggressive and releases more vent-gas.Detecting battery failures immediately after the first venting is critical to take action before the failure evolves into a thermal runaway event. Therefore, a gas detection method targeting first venting gas will be the focus. Early studies of first venting gas composition showed that CO2 is the primary gas component in battery overheating tests, nail penetration tests, and overcharging tests, while the gas composition in battery external short circuit tests was not revealed.To this end, an external short circuit test for a pouch 4.6 Ah cell was performed in a non-sealed acrylic box, which has around 21.5 L volume. Shortly after the initiation of external short circuit, the battery expansion force rises due to gas generation inside the pouch cell. The force then dropped suddenly indicating a gas venting event, which occurred when the cell temperature reached 114 °C. A Non-Dispersive Infrared (NDIR) CO2 sensor was used. The CO2 sensor reading started to increase within 5 seconds of gas venting and reached a maximum of 1,500 ppm as shown in the figure.To apply the gas detection strategies for first venting events, a detection threshold is required for different cells at different abuse conditions. To model the gas evolution process, the evolution of side reactions, mainly the SEI decomposition at high temperatures was considered. The released CO2 in first venting events can be estimated at different abuse conditions. The estimated CO2 amount can help determine the detection threshold of gas concentration for a given battery system. Figure 1