A game changer in E-mobility?

As the market for electric mobility continues to grow, the need for efficient technology to keep batteries cool has become increasingly important. Batteries are a core part of electric vehicles and are critical to their longevity, reliability, and performance. Ensuring that the battery temperature is kept within safe limits is essential to guarantee the vehicle's safety, durability, and overall performance.

This article will look closer at immersion cooling technology within electromobility and how it compares to more commonly used technologies. Currently, immersion cooling is not widely used within electromobility. Small vehicles such as electric bicycles or scooters usually have no designated cooling system but only give heat to the surrounding air via convection. This is simple and cheap but does not provide reliable cooling. Plate-to-liquid cooling is used in motorbikes, cars, and more oversized vehicles. Plate-to-liquid cooling is controllable via coolant temperature and flow. It can have significant cooling power, especially with a chilling unit. In plate-to-liquid cooling, the modules or cells are in contact with an aluminum plate, which in turn comes into contact with the coolant.?

Even though plate-to-liquid cooling generally does a good job keeping batteries in the preferred temperature range, it performs suboptimal in keeping batteries cool during high power demands as cell-internal temperatures rise quickly.

The path through the aluminum plate to the coolant creates a high thermal inertia. In addition, designing a plate-to-liquid system that cools all cells evenly is challenging. Battery temperature is crucial in aging, and just a few degrees difference significantly impacts a cell's lifetime.

As the performance of a battery module is disproportionally influenced by its weakest cell, one poorly cooled cell can pull down the version of the whole module.?

What is immersion cooling??

Immersion cooling is a technique originating from computer cooling, in which electrical and electronic components are submerged in, hence in direct contact with, a thermally conductive but electrically insulating liquid. This principle can also be applied to batteries. Immersion cooling is highly effective because liquids fill gaps, providing maximum contact surface to the cells for heat transfer to coolant. Additionally, no medium between the cell and the coolant means lower thermal inertia and a faster cooling effect. Immersion cooling can work as so-called two-phase cooling, meaning the coolant may undergo a phase change from liquid to gaseous while in the circuit, allowing for far greater heat absorption. However, this requires special liquids with fitting boiling points.

The required dielectric fluids often have a lower thermal conductivity, specific thermal capacity, and higher viscosity than regular coolant. Hence, they require higher fluid flow rates and pumping power. In addition, immersing cells entirely in liquid brings new requirements to the cell design, such as waterproofing. This is not a given for standard cells, which often have venting holes to allow gas release and pressure limiting in case of thermal runaway.?

Is immersion cooling better??

Immersion cooling offers significant advantages for electric vehicle batteries over plate-to-liquid cooling. The degradation process of batteries can be slowed with immersion cooling, where the cooler, more homogeneous temperature helps to reduce chemical reactions better for each individual cell. By doing so, the lifespan of the battery is extended.

During high power demands, immersion cooling is capable of taking the heat generated by the cells more quickly, keeping the cells cooler and hence not only increasing the lifespan of batteries in high-power applications but also improving efficiency: Colder components have higher electrical conductivity.

This goes also for the busbars, which can easily be integrated into the same immersion cooling system as the cells.?

This technology also improves safety by reducing the risks associated with thermal runaway and electrolyte leakage by effectively taking away the heat right from the source. This can prevent thermal runaways happening in one cell from spreading to neighboring cells and, according to some sources, even stop thermal runaways from happening altogether.?

Besides the benefits immersion cooling offers to the e-mobility industry, it also has many challenges that make it not widely used. The main factors are financial: Higher development and production cost and maintenance. Specialized liquids come at a higher price than other existing cooling systems but are essential for immersion cooling. Upkeep requires expertise and knowledge, leading to an increase in maintenance costs. Finally, having coolant fill and flow through the battery packs themselves requires the whole system to be watertight and extensive fluid-dynamic and thermal development for the system to work as intended.?

Exemplary applications?

Immersion cooling is already applied in multiple high-performance vehicles, such as Formula-E. Applications in the high-volume passenger car market still need to be created.?In mid-2021, TotalEnergies and Ricardo plc presented "A world-first road car fitted with immersion cooling."

A Volvo XC90 plug-in hybrid had its battery cooling system replaced with an immersion alternative without any modification to the design of the battery or vehicle.

TotalEnergies claims that the results were faster charging, better cooling, enhanced safety, and lower cost/mass. Ricardo plc states that immersion cooling technology will enhance the life of the battery by about 20%, improve safety by containing thermal runaway, and reduce the cost of the battery pack by up to 10%, along with reducing charge time significantly.?

The McLaren Speedtail, a limited-production hybrid sports car, also uses this technology. The cells of its battery are permanently immersed and thermally controlled by a dielectric coolant, which quickly moves heat away from the cells. This allows a 1.65kWh Lithium-Ion battery pack to feed a 230 kW electric drive as part of a 770 kW powertrain.?

The implementation of this technology by the retrofitting project of TotalEnergies and Ricardo plc, as well as in a production road car by McLaren, mark significant milestones, showcasing the potential of immersion cooling by enabling the battery cells to operate at higher intensities and extended durations.?

Conclusion?

Immersion cooling is not the holy grail of battery cooling, but it will undoubtedly play a role in the future of the e-mobility sector. Its high costs and complexity will make it hard to justify for lower-performance mass applications. Still, it has advantages that no other technology can achieve, especially for high-performance applications. Exemplary applications show that the technology works technically; some even claim financial benefits over conventional solutions. Seeing how this technology advances in the next decade will undoubtedly be interesting.?Care to continue this discussion? Get in touch with us today!