Conventional battery pack sensors measure the voltage, current and temperature of cells within the pack. However, it is increasingly clear that additional sensors would significantly enhance safety and allow for early warning and even prevention of thermal runaway, and in turn battery fires, in electric vehicles (EVs) and energy storage systems (ESS). Gas sensors, pressure sensors, moisture sensors, humidity sensors and aerosol sensors can all play a role. The market for these sensors is growing and is expected to exceed US$200 million by 2036, with gas sensors making up over 73% of the market. To find out more, see the associated report, "Advanced Battery Pack Sensors and Remote Monitoring 2026-2036: Technologies, Markets and Forecasts".
The stages of thermal runaway
Thermal runaway describes a chain reaction that occurs in batteries, caused by component damage or environmental conditions. High temperatures or short circuits are leading causes. An initially high temperature causes battery component degradation, which in turn leads to exothermic reactions that release more heat. This extra heat then fuels further reactions, increasing the temperature of the cell. This leads to further degradation and the cycle continues. Without sufficient thermal management, thermal runaway can propagate between cells, leading to battery fires which can risk lives and damage vehicles.
Battery decomposition during thermal runaway. Source: IDTechEx
Thermal runaway can be broken down into different stages, determined by the temperatures at which the different cell components decompose. Before full runaway occurs, various gases are produced due to component degradation, including volatile organic compounds (VOCs), hydrogen, carbon dioxide and carbon monoxide. These gases can be flammable and toxic, and through their production, the pressure inside the cell rises until the cell vents and gases released into the battery pack enclosure.
Mitigating runaway through advanced sensors
Conventional methods of detecting thermal runaway focus on current, voltage and temperature sensing. While these are usually sufficient when the vehicle is in-use, they provide no warning when parked due to the lack of power supply to the sensor nodes. In addition, they are not always effective in preventing thermal runaway propagation, nor do they allow for detection of gases after cell venting, which can still be dangerous even when runaway propagation is prevented. Advanced sensors add additional avenues for runaway detection and can allow for monitoring of cell venting. The ideal sensors for runaway detection are gas sensors, pressure sensors and aerosol sensors as all three of these are produced during battery pack degradation. Gas sensing is especially interesting, as it allows for detection of cell venting, and provides earlier and more reliable warning than pressure or aerosol detection.
Suitable hydrogen sensors are often based on the principle of thermal conductivity: air with high levels of hydrogen is more thermally conductive than normal. This allows for a measurement of hydrogen concentration. Hydrogen is produced during cell venting and during thermal runaway after evaporation of the liquid electrolyte. By monitoring hydrogen levels, earlier warning of thermal runaway can be given, preventing runaway propagation and allowing for detection of dangerous hydrogen build-up within the battery pack (which can cause delayed explosions and fires when exposed to a spark). Volatile organic compounds describe various liquids present in the battery pack, including hydrocarbons and electrolyte vapors. They are one of the first gas types to be produced during electrolyte evaporation, and thus provide extremely early warning of thermal runaway. Carbon dioxide and carbon monoxide sensors can also play a role in providing early warning of thermal runaway, though the technologies for these sensors tends to be more expensive and harder to integrate directly into the battery pack.
The role of regulation
Currently, regulations around the world require only that electric vehicle users be given a 5 minute warning before any fire or smoke enters the passenger area of the vehicle. This places no responsibility on battery pack developers to provide warning of the presence of dangerous gases in the pack, e.g. through gas or pressure sensing and monitoring of cell venting events. The result is various electric vehicle fires that have occurred while the vehicle was parked, when conventional sensor deployments were offline. Even when the vehicle is not in use, risk to life is legitimate. But without further regulations, most automotive developers will continue to use only conventional sensors, in order to avoid (relatively small) additional costs. It is expected that in the coming decade, additional regulations are put into place, requiring the use of advanced sensors in battery packs, for electric vehicles and energy storage systems both.
An evolving market
The full advanced sensors market for battery packs includes a wide array of sensor technologies, such as chemi-resistors, thermal conductivity sensors, non-dispersive infrared spectroscopy sensors and more. Moisture and humidity sensors are also expected to see increasing usage, due to relatively low costs, and the potential for prevention of battery pack component degradation, and in extreme cases, thermal runaway events. IDTechEx predicts that over the next ten years, the market will have expanded significantly, and advanced battery pack sensors will see widespread adoption across the automotive and energy storage industries. For more information, see the associated report, "Advanced Battery Pack Sensors and Remote Monitoring 2026-2036: Technologies, Markets and Forecasts".
For more information on this report, including downloadable sample pages, please visit www.IDTechEx.com/ABP, or for the full portfolio of Energy Storage research available from IDTechEx, see www.IDTechEx.com/Research/ES.
