Why thermal management fluid is critical for safe EVs

Electric vehicles (EVs) are transforming the automotive industry, providing cleaner, more sustainable alternatives to traditional internal combustion engine (ICE) vehicles. However, their continued reliability depends on one critical factor: thermal management.

Maintaining the optimal temperature for EV batteries and components is essential. Without proper thermal regulation, EVs face serious challenges, including performance issues, reduced battery life, and in extreme cases, serious safety risks like thermal runaway. Developing effective thermal management systems might sound straightforward, but it’s easier said than done.

Figure 1. Keeping EV batteries cool is the most common thermal management concern. Advanced cooling solutions help extend battery life by preventing overheating and minimizing corrosion.

As EVs must function reliably across diverse climates, one challenge is maintaining a stable operating temperature. Another challenge is energy efficiency. Whether used for cooling or heating, thermal management systems consume energy, which can significantly impact the vehicle’s overall efficiency and driving range. Managing the balance between optimal temperature control and energy preservation is crucial to an effective thermal management system.

In addition to climate regulation, these systems must manage the high heat loads generated during EV fast charging and heavy usage. This requires an efficient solution capable of consistent thermal regulation.

“Many EVs rely on coolants or thermal management fluid to provide heat dissipation and temperature stability,” shares Matt Kern, senior director of Global Sales at Prestone. “Both are essential for maintaining optimal battery performance and extending component lifespan.”

Liquid coolants with high thermal conductivity quickly absorb and dissipate heat, preventing overheating and ensuring stable temperature control. This protects the battery and key components, allowing for efficient and reliable operation.

However, the ideal coolant chemistry is critical. This fluid must not only perform efficiently under demanding conditions but also be compatible with an electric vehicle and its high-voltage components.

“To properly manage the temperature, two things must be done,” explains Kern. “One is that it’s important to protect the system that the coolant or thermal-management fluid is in. Secondly, if that coolant happens to get on the vehicle’s battery, maintaining a safe environment is paramount.”

In an EV, a safe environment is one with optimally functioning components. This means the coolant used must not only provide effective heat dissipation but also prevent corrosion.

“Water and ethylene glycol are the two main components of a thermal management fluid, and both are potentially corrosive,” he says. “So, you actually have to protect the vehicle and its components from the coolant itself.”

As a result, safety must be attained by ensuring corrosion is minimized in the thermal management system. This requires developing unique and effective non-corrosive coolant chemistries not previously used in the automotive industry.

Figure 2. In the case of a leak or impact, the conductivity of thermal management fluid is directly related to compatibility with battery components.

“This alone is difficult,” adds Kern. “What’s more, we must safeguard against leaks but, as a precaution, also prepare for their potential occurrence. So, if for whatever reason — say, a crash or an unexpected catastrophic event — the fluid leaked onto the vehicle’s battery or electronic components, it does not result in a fire.”

Ensuring corrosion inhibition in the thermal management system while maintaining low conductivity is critical, as Kern suggests, but extremely challenging.

“The problem here is that the more corrosion inhibitors introduced in the coolant, traditionally the greater the conductivity. This is what typically happens if you rely on the standard inhibitors used in antifreeze coolants. The conductivity isn’t exactly safe for an EV.”

The EV revolution

Coolants were first introduced to ICEs in the early 20th century, around the 1920s. As engines became more powerful and vehicles were driven longer distances, more effective temperature control became necessary.

“Antifreeze coolants performed the job of preventing engines from freezing and boiling over,” says Tom Corrigan, director of EV technology for Prestone. “Today, more advanced coolants have corrosion inhibitor packages to prevent rust and corrosion from forming.”

Initially, when electric vehicles hit the roads, the same coolants used in ICE vehicles were used because they performed well. But what works for one system doesn’t always apply to another.

“Beyond corrosion, it became clear that these coolants interacted with high-voltage components somewhat differently. An impact like a crash could result in a broken cold plate or cooling tube, which meant this fluid would leak into the battery pack,” Corrigan explains.

The high-conductivity coolants commonly used with ICEs risked thermal runaway in battery-powered vehicles. Traditional ICE coolant corrosion inhibitors, due to their ionic nature, increase conductivity. Removing them from formulations lowers conductivity but at a cost.

“Unfortunately, traditional ICE coolants used in EVs led to too many risks. So, the move had to be to a lower conductivity coolant, which could no longer pass electricity. The sacrifice here, of course, is corrosion.”

Corrigan points out that some low-conductive coolants initially available for EVs caused massive corrosion within their thermal management systems. Eventually, such corrosion leads to enough damage that the coolant leaks. Ironically, the other problem is that it reduces thermal efficiency, the very thing it’s meant to control.

Figure 3. The proper formulation of corrosion inhibitors can greatly increase the lifetime of system components.

“What happens is, low conductivity fluids tend to leave corrosion deposits (with high thermal resistivity) on the heat exchangers, which begins losing efficiency,” he says. “Now, it’s no longer possible to control the battery temperature as desired, and the vehicle loses driving range and sacrifices charging time to the excessive heat. So, corrosion can lead to leaks and thermal inefficiencies.”

Fortunately, new coolants for EVs are being developed to reduce corrosion and enhance compatibility with sensitive battery and electronic components. Some of these formulations can offer improved thermal conductivity, ensuring faster heat dissipation and better temperature stability under extreme conditions — ultimately providing greater safety.

“There’s a lot of research and development related to thermal interface materials, including gap fillers and aerogels, which are all used to direct heat away from the battery cells into the cooling plate and then into the fluid, right? So, a high-quality thermal management fluid lowers this heat and then carries it away,” says Corrigan. “Lowering heat is absolutely critical for the safe, effective, and long-lasting performance of any EV.”

What to look for…

Ideal thermal management fluids for EVs should possess the following characteristics:

High thermal conductivity: Efficiently transfer heat to and from critical components.
High specific heat capacity: The amount of heat absorbed per mass of fluid
Wide external temperature range: Perform reliably in extreme temperature conditions.
Chemical compatibility: Compatible with materials used in the cooling system.
Non-corrosiveness: To avoid damaging components over time.
Low viscosity: Minimizes energy consumption of the circulation.
Low environmental impact: Reduce environmental harm throughout their lifecycle.

Fluid innovations

Thermal management fluids for EVs typically use a glycol base but that’s evolving. These fluids have been effective but have limitations in terms of thermal conductivity, compatibility, and environmental impact.

More recent innovations include:

Nanofluids: The addition of nanoparticles to traditional fluids can significantly enhance thermal conductivity.
Phase change materials (PCMs): These materials can absorb and release heat as they change from solid to liquid and vice versa, providing efficient temperature control.
Ionic liquids: Non-volatile, non-flammable, and non-toxic, ionic liquids offer a safer alternative to traditional fluids.
Graphene-based fluids: Graphene’s exceptional thermal conductivity properties make it a promising candidate for thermal management applications.