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Battery safety testing usually involves the use of specialist facilities that can subject batteries to extreme conditions, allowing analysts to evaluate their performance and safety under various normal and abnormal operating conditions. But once a battery pack has been installed in a vehicle, how can we check up on its health?
The most traditional way to do this is via the vehicle’s embedded battery management system – an electronic system that continuously monitors and manages the voltage and current of the battery pack, overseeing and ensuring its correct function.
But other signs can also indicate a battery at risk of starting a fire or explosion. Off-gassing, where a cell begins to release gases as a consequence of its internal components breaking down, can be an early warning sign that a major thermal incident is on the way.
Metis Engineering, a British-based developer and manufacturer of advanced sensors, has developed an environmental sensor designed to monitor critical parameters for battery health, including off-gassing, as well as moisture ingress and impact detection. In addition to this, the company has also developed hydrogen sensors and air quality sensors that can further ensure safety in the world of electric vehicles and hydrogen fuel systems.
To learn more about how environmental sensors can be deployed to great effect in the battery industry, as well as in hydrogen storage, Technology Networks spoke with Joe Holdsworth, founder and CEO of Metis Engineering.
Can you tell us more about Metis Engineering and what you do?
Joe Holdsworth (JH):
Metis Engineering was founded in 2016. Initially, it was just me contracting but, over time, I started to develop electronics and move towards something more product-based. The first [sensors] Metis started making were inertial measurement sensor units. Then we developed a battery safety sensor, and that is where the Cell Guard came from.
Now, we have the Cell Guard, the H Guard (which is a similar sensor but for hydrogen systems) and we have the Air Wise for heating, ventilation and air conditioning (HVAC) systems. But we have also started to develop some other sensors outside of gas sensing to diversify a bit. For example, we have an analog-to-digital controller area network (CAN) module and we’ve also done thermocouple-to-CAN modules aimed at test houses where they might be testing high-voltage battery packs and they need electrical isolation across the thermocouples that you might place.
What is the Cell Guard? Why is a gas sensor useful for battery safety monitoring?
In an electric vehicle, you’ve got your battery management system that looks at voltages and cell temperatures, and they are quite useful systems for looking at problems within the battery pack. In the short term, though, by looking at voltages in a battery pack, it might be difficult to assess whether there are issues, because if you’ve got a lot of cells in parallel, they might mask the cell with a problem. As for monitoring temperature, although it’s a good way to look for problems, you don’t typically have temperature measurements on every single cell.
If you are looking for problems in the battery pack, the other way to do this is by looking at off-gassing from the cell, which is where the Cell Guard comes in. It looks at the gas that is produced from the cell and tries to detect if there are the beginnings of a thermal event. But it can also look at moisture ingress, impact detection and volatile organic compounds (VOCs) as a method of looking for thermal events inside the pack.
In terms of these thermal events, like anything that is manufactured, there is a certain tolerance – a variation inside the cells over a period of time. Those tolerances can become more pronounced, which might lead to a cell in the pack being weaker than the other cells around it. If that cell doesn’t have a temperature sensor on it and it’s masked by other cells, you might not pick up any issues with it.
These issues can cause the cell to get hot, then that cell can start venting (releasing gas). If nothing is done about that, it can lead to a thermal event that will set some of the other cells off. The aggressiveness of thermal propagation does depend on cell chemistry, but even in lithium iron phosphate (LFP)-type cells, you’re still going to see a lot of gas and heat production, which can be explosive.
A battery experiencing thermal runaway. Credit: Metis Engineering.
How can environmental sensors be deployed to have maximum impact, in the battery industry but also in other sectors?
The Cell Guard was developed for battery packs, but, like anything, usually your customers find lots of other different uses for it and it ends up going into lots of different places. So, for the Cell Guard, that has meant energy storage, all sorts of vehicle types, laboratory situations, etc. It goes into a lot of different things, even though we built it for vehicles.
The H Guard is really new, so we’re yet to properly see what our customers end up applying it to. Although we know that some customers want to put it into an exhaust or a fuel cell, which is typically high in moisture and involves high temperature; the sensor currently can’t do that. The H Guard is designed to look for leaks in hydrogen systems – it is very similar to the Cell Guard, but just differentiated to show that it is intended for hydrogen applications – and can be placed elsewhere in the system, wherever you might want to pick up a leak. Right now, it’s being used to look for leaks in hydrogen storage applications.
As for the Air Guard, it looks at carbon dioxide, VOCs, nitrous oxides, moisture, air temperature and other things. There is also one in development looking at particulates. This sensor incorporates all types of things that you might want to look at in an HVAC system or inside the cabin of a car or a bus. It will look at air quality, and then you can adjust your control system in terms of ventilation to try and bring things down to the safe levels that you want.
Truly, we usually have an idea of what we’re working for, but the customers are very inventive and will always find uses for these sensors on other stuff!
Looking to the future, are there any advances in sensor technology that you are particularly excited about that are on the horizon?
The miniaturization of sensors is great. There are new sensor technologies that are coming out, particularly in terms of very small package sizes that I’m interested in looking at – either with a view of upgrading these sensors or addressing some of the weaknesses of this detection method. But definitely the miniaturization of sensors is a very cool field and there is loads of interesting stuff coming in this area.