Electrolyte detection is a possible way of seeing early cell failures where a soft vent results in electrolyte being vented and dispersed into the pack volume. This soft venting of electrolyte happens prior to a cell going into thermal runaway.
Liu et at [1] look at the development of an electrolyte sensor that measures Ethyl Methyl Carbonate (EMC). They show that it is possible to measure EMC in the low ppb and within ten’s of seconds. Cai et al [2] looked at the gas composition from different cell chemistries under different abuse scenarios, their view was that CO2 was the most common and robust gas to detect.
Alarmingly, research suggests that many instances of thermal runaway in Li-ion systems occur without any known damage to the battery. As a result, such events can only be effectively mitigated through the use of robust early detection systems. Gas sensor technology is key to this.
Because thermal runaway is an uncontrolled chain reaction, detecting the gases that indicate an event as rapidly as possible is crucial.
When this multi-phase process starts, a battery cell typically vents evaporated electrolyte at high temperatures. While voltage and temperature often react slowly to this initial venting; gases, smoke, and pressure served as reliable rapid indicators that such a failure is taking place.
Amphenol [3]
Honeywell [4] describe the runaway event and gases in more detail:
During a thermal runaway event, various gases are released. In the early stage, the cell vents a high concentration of electrolyte vapor. This includes gases such as Ethylene carbonate (EC), Diethyl carbonate (DEC), Ethyl Methyl carbonate (EMC) and Dimethyl carbonate (DMC) etc.
As the event progresses to an explosion, there is an increase in H2 and CO.
Honeywell [4]
In a Honeywell test where a pouch cell is overcharged at 2C rate to induce thermal runaway or explosion, the BES sensor alarms ~7 minutes before thermal runaway and H2 , CO, CO2 and CH4 gas sensors showed ppm response only during the cell explosion/thermal runaway.
This shows that new designs with integrated sensors are a way of getting an earlier response to a possible thermal runaway and can give enough time to shut down and mitigate a thermal propagation event or to give an alarm that would allow people to get to safety.
Honeywell BES
Sensing:
- Battery electrolytes
- Hydrogen
- Carbon monoxide
- Humidity (customizable upon request)
- Pressure (customizable upon request)
- Temperature
Specifications: BES Series, Honeywell
Li-Ion Tamer
This is a master and distributed sensor system with a typical installation:
- Monitoring sensors installed at the battery racks – downstream convective airstreams – to monitor off-gas events
- Reference sensors installed to monitor the ambient environment and air inlets to prevent false positive signals
- Hubs installed local to their respective zone of sensors
- Controller and Ethernet switch for aggregating sensor signals (optional PoE switches for distributing power to the system)
Specifications: Li-ion Tamer Monitoring Sensor, Gen 3, eurofyre
- Chengao Liu, Jie Wan, Wenbo Dong, Xiaoxia Wang, Jianfa Chen, Shasha Li, Chengli Mao, Dawen Zeng, Rapid detection of ppb level electrolyte leakage of lithium ion battery（LIB）by WO3 hollow microsphere gas sensor, Materials Today Communications, Volume 35, 2023
- Ting Cai, Puneet Valecha, Vivian Tran, Brian Engle, Anna Stefanopoulou, Jason Siegel, Detection of Li-ion battery failure and venting with Carbon Dioxide sensors, eTransportation, Volume 7, 2021
- Gas Detection for Thermal Runaway Prevention in Lithium-Ion Batteries, Amphenol Sensors
- BES Series, Honeywell
See also: Early & Passive Thermal Runaway Detection, Gas Sensing, Leak Detection