In recent years, the automotive industry has experienced a significant shift towards electric vehicles, driven by the growing awareness of environmental concerns and the need for sustainable transportation solutions. As the demand for EVs continues to grow, it’s important to guarantee the battery safety, longevity, and the efficiency of their energy sources. A groundbreaking technology: Immersion Cooling, is a revolutionary approach to thermal management associated with electric vehicle batteries.

The benefits of immersion cooling for EVs

Optimum safety: fire protection system

EXOES has developed an immersion cooling technology that prevents the spread of thermal runaway inside the battery. In the event of a battery cell failure, its energy is efficiently distributed to the whole battery, avoiding the dangerous overheating of surrounding cells. Gazes releasedby cell rupture are also safelymanaged outside the battery module.

Increased EV lifetime

Immersion cooling provides a better environment for the battery. By cooling several cell faces directly, the temperature across it is spread out more homogeneously. Even in difficult cycles, the cell temperature gradient (from one extremity of the cell to the other) remains very low: down to 5°C during fast charging. This reduces cell degradation over time, enabling a longer life cycle.

Reduced charging times without damaging the battery

Combining immersion cooling with proprietary algorithms to model cell anode potential, EXOES batteries exploit the full potential of their cells, achieving higher performance than specified by manufacturers. On a 60Ah NMC622 cell, a charge time of 13 minutes (20 to 80%SOC -~3C) was achieved without any capacity loss (5% loss over 750 cycles) instead of the 35 minutes (~1C) specified by the manufacturer.

Immersion cooling technologies for EVs

The different immersion cooling methods

Immersion cooling technologies include all cooling architectures where the coolant is in direct contact with the component. EXOES has studied several architectures for immersion cooling: partial/full immersion/spray, circulating / static, single phase /2 phases … Currently, most of the batteries designed by EXOES are full immersion architectures using single-phase circulating coolant.

Different fluids are used for battery cooling

EXOES has tested over 40 different dielectric fluids for battery immersion cooling, expanding its expertise to understand which is the best candidate for a given battery application.

– PAO base oils are cost-effective and provide sufficient viscosity as well as good material compatibility with the battery system.

– Esthers are more environmentally friendly fluids that can be organic-sourced and degrade quickly in the environment.

– Finally, hybrids and blends using additives can be formulated to meet any specification.

Current research and development

Recent technological advances in immersion cooling for EVs

Like many innovative technologies, immersion cooling will first be tested in high-performance applications such as racing and hypercars. For these applications, the requirements are mainly focused on optimum performances and the highest possible C-rates. However, immersion cooling is also being considered for a mass market application for vehicles being developed for 2028 – 2030, especially for the greater safety it provides. When considering a product that will be manufactured in thousands, additional requirements must be validated such as production costs, weight, compactness, and vehicle integration. EXOES is leading immersion-cooled battery development programs that integrate all these constraints while delivering performances and safety features in line with a new generation of requirements and standards for mass-market EV batteries.

Current research projects

One topic related to battery immersion cooling is safety requirements for battery testing. The risks associated with battery testing are described in the EUCAR matrix from electrical hazards to toxic fumes, fire, and explosion. To demonstrate immersion cooling to prevent the propagation of thermal runaway, while providing unique safety features, severe abuse tests are required. These tests are carried out in the worst conditions of the OEM’s DFMAs.

Therefore EXOES has developed expertise in designing and manufacturing safe battery test benches to safely operate and monitor advanced battery testing while managing all hazards in case of battery failure, fire, or explosion.

As battery safety requirements evolve, so will battery standards and testing methods. EXOES is committed to providing the most relevant tests to assess the safety for next generation batteries thanks to an advanced understanding of battery failure mechanisms.

Future developments

Future trends in the use of immersion cooling for EVs

Immersion cooling needs an additional cooling loop in the vehicle for the dielectric fluid. This is an opportunity to use the new cooling loop to cool the other vehicle components and the battery. Direct oil cooling of the e-motor is already a mature technology, and power electronics are also a good candidate for direct cooling. Ideally, replacing the water-glycol loop by a dielectric fluid loop would save complexity in vehicle integration while delivering better performances in terms of both components and system. This advanced architecture is a technical challenge as all components have different operating temperatures. Therefore, it will likely be reserved for high-performance vehicles soon.

Regulations and standards

Safety and performance standards

There is currently no standard for testing immersion-cooled batteries. This thermal management system introduces new variables such as coolant flow rate, pump activation trigger, fluid filling…

In collaboration with other leading immersion cooling companies, EXOES is creating the DIRECT COOLING CONSORTIUM to help regulators define relevant test standards that will accelerate the industry’s adoption of immersion cooling, not only for the battery but for the e-motor and power electronics as well.   

As the automotive industry evolves towards sustainable transportation, EXOES’ leadership in immersion cooling positions them as key contributors to the ongoing evolution of EV technology, with a focus on safety, performance, and environmental awareness.

For more information about battery safety and test benches: