Immersion beaters

When TotalEnergies was looking for a project partner for its immersion cooling technology for batteries, Ricardo was the ideal candidate. John Challen explains why.

A player in the market is French integrated energy company TotalEnergies, which has created an immersion-cooled battery technology for EVs. When looking for a project partner, Ricardo’s experience with thermal management helped it win the contract. “During our discussions, Ricardo understood very quickly what we wanted to achieve, which meant we had even more confidence in their capabilities,” recalls Gérard Quoirin, Product Engineer Battery Fluids for TotalEnergies.

While immersion cooling has been used in niche applications from other vehicle manufacturers, the project – dubbed Phosphor – represents a world-first mass production vehicle with the technology. It aims to improve battery thermal management, the main benefits to the vehicle being faster charging times, better performance and lower prices. Solutions such as the one at the heart of Phosphor replace the traditional traction battery cooling system with the immersive one.

Within Phosphor, the battery is cooled with dielectric fluid, which enables a higher power capability than the systems already currently available on the market. That higher power, says Quoirin, can reduce charging times from two hours to 30 minutes.

This time reduction was an important factor and, as Quoirin points out, indicates how expectations when running EVs have changed: “EVs have evolved very quickly and now there are bigger batteries and much more performance. But it’s clear that from 2026 or 2027, it will be difficult for Original Equipment Manufacturers (OEMs) to sell a vehicle if you can’t recharge it in less than half an hour.

“In five years’ time, customers won’t want to wait three hours to charge their vehicle. To fulfil these desires, we need to increase the power of the charge and offer a bigger cell capacity. Constraints of the cooling system will be higher and the current technology can’t manage the heat generated by the cell,” adds Quoirin. “Immersion cooling is a solution and Phosphor demonstrates how it is possible.”

Making comparisons

To make life easier, TotalEnergies and Ricardo kept the dimensions of the cooling system the same but simplified the design. “We could have changed everything, with a design that was 100 per cent optimised for immersion cooling, but then making a comparison between the car with immersion cooling and without it would be more difficult,” explains Quoirin. “We decided not to change the number of type of cells, therefore the battery volume remained constant.”

TotalEnergies and Ricardo used a production vehicle – a Volvo XC60 plug-in hybrid – although a wide range of applications are possible, says Quoirin. These include static storage systems, trains and off-road applications. “We made the modifications on an SUV because it was easier to identify the improvements,” he says. “But we benchmarked all vehicles on the market.”

The timescale of the project – work started in November 2020 and was completed by April 2021 – meant face-to-face time was limited due to Covid-19 restrictions. Therefore the majority of the discussions between the Ricardo and TotalEnergies teams were done remotely. That, according to Quoirin, didn’t pose a problem: “I was on the project 100 per cent and supported by different colleagues, but most of the work – including the final product review – was done via video conferencing. It would have been better if we could have completed the project in person, but we didn’t have an issue.”

This situation meant that Ricardo was responsible for the four key elements of Phosphor. “The first phase was a feasibility study, which included numerous tests on the original base vehicle so we had a reference point,” recalls Quoirin.

“The second phase was dedicated to the design of the new batteries and the validation of the changes. When the design for the new cooling system was frozen, the Ricardo team undertook physical verification of the battery and then the vehicle.”

The final phase saw Ricardo engineers repeat the original tests, using the new battery and immersion cooling system, comparing it to the results from stage one.

Weight and cost savings

Overall the project was a success but there were challenges. “We had a hurdle to overcome with thermal runaway because there were so many scenarios to be considered,” says Quoirin. “Another challenge was finding the right materials because we discovered some materials were not compatible with each other in the new design. Unfortunately, the list of materials that we could use was limited but we knew the most important thing was to optimise the design of the battery and reduce the volume necessary to achieve the desired level of cell cooling.”

In contrast, there were a couple of highlights that stick out for Quoirin, including testing the battery to its limit: “We claimed that immersion cooling can prevent fires breaking out. Therefore we tested the theory by first taking the original battery and module from the Volvo and heating one cell and after one hour, the module caught fire,” he recalls. “However, when we repeated exactly the same test on the immersion cooled module, we exposed it to heat for seven hours and nothing happened. So we arguably have the safest batteries in the world!”

Another big positive was the realisation that immersion cooling can reduce the weight and cost of the car. “We can reduce the cost of the battery by six per cent, which can be quite a lot of money,” Quoirin adds. “The battery is cheaper because the design is more simple. Today, the assembly of the current battery cooled by standard technology is quite complex. For example, it requires several ports, aluminium components and thermal pads to get the best contact between the cell and the cooling plate. All of those parts are very expensive. By comparison, immersion cooling is very simple – the cell just goes inside the dielectric fluid.”

With the project now complete, the next phase is talking to battery and vehicle manufacturers to show them the advantages of immersion cooling – a process that has already begun, says Quoirin. “Their first feedback is surprise – after that they are excited because they can see we have a real solution to the problem.”