Electric vehicle (EV) batteries are heavy, with the average EV car battery weighing in at several hundred kilos. Whilst load cells have long been used to weigh EV batteries during the development stages, they are also helping manufacturers to make smaller lighter batteries that are safer and also more energy dense.
Multiple cells, one battery
The current generation of EV batteries are an array of individual cells, placed in modules and linked to form one big battery. They also need to be reliable and robust, as an article in Car magazine explains:
“(EV batteries) need to be able to store a lot of energy, but also recharge quickly, and retain their energy density over many thousands of charging cycles, all the while being pummeled by roads, potholes and whatever the great British weather throws at them…”
Li-ion EV batteries: taking the pressure
EV batteries can either be lithium-ion, or solid state. Most in existence and being manufactured are lithium-ion EV batteries which contain liquid. This makes them soft and means that they expand and contract across a larger range. When the battery charges, each cell heats up and expands, and then contracts as it cools down. This can result in a build-up of pressure inside the battery stack.
Developers have been aware of these issues for almost a decade. A 2014 study by Princeton University measured the pressure using a load cell in the stack. They found that:
“Initial compression and force were negligibly low, followed by a modest increase. They conducted a number of tests and discovered that there was a sweet spot where the battery would age more gracefully if the pressure was in the proper range.”
In 2017, the University of Warwick took that research a stage further, and placed a load cell that measured the total force exerted on the stack itself. The team found that:
“Some cells would malfunction in specific regions where there was an increase in localized pressure. There was also a strong correlation between this and the battery’s life and degeneration.”
It’s the localisation of the load, rather than the overall pressure, that is more likely to result in a malfunction.
According to an article in Electronics Online, one EV battery manufacturer tested for this build-up of battery stack pressure using:
“A compression button load cell in between two garolite end plates, and measuring the force due to cell swelling or expansion. Instead of monitoring through voltage (ICV), this method is based on measured force (ICF). To monitor the testing, the load cell was paired with (a) high speed data logging indicator. This instrumentation solution provides the ability to display, record and log the force measurement results with supplied software.”
A tyre-ing journey
Interestingly, load cells are also being used by tyre manufacturers to assess the differences between tyre wear on electric and combustion engine cars. Since EV engines have considerably more torque when first loving off, EV tyres could wear out more quickly. The data from the load cells in testing are helping manufacturers develop different composition and tread patterns for EV vehicle tyres.
New life for old EV batteries
Given that EV batteries contain so many rare (and expensive) elements, it’s important to ensure they deliver a nett positive environmental benefit over their lifetime, and hopefully beyond. Car magazine has some reassuring words:
“There are so many cells in a typical EV battery that they retain capacity even after hundreds of thousands of miles … the internet is full of high-mileage electric and hybrid cars still working well into their dotage. The expected electric car battery life is at least a decade and our advice is your car will fall apart before your battery fails.”
We also like the idea that when your electric car battery is no longer able to power your vehicle, it can be removed and used to store energy from off-peak supplies or solar panels for use in your home via a smart energy system.
Load cells and testing
Our load cells are used extensively by R&D departments across a wide spectrum of industries, from materials testing to equipment road testing. We also work with clients to design bespoke solutions and load cells as required. Contact us with your requirements, or if you know what you need, buy online today. We design and manufacture our own range of load cells right here in the UK, so there’s no worries about shipping delays!