To tackle the effects of climate change, more countries around the world are starting to take action to wean themselves off fossil-fuel-based transportation options such as internal combustion engine (ICE) vehicles. Norway, for example, has passed legislation that will ban ICE vehicles entirely by 2025, and other countries are slowly inching in that direction as well.
While ICE innovation continues, the expectation is that electric vehicles (EVs) will make up a larger portion of new car sales. In recent years, however, reports of fires caused by overheated batteries have led some to question whether EVs are safe for long-term use.
The key to EV safety is to monitor and manage the charging, discharging and temperature of the battery. Initially, original equipment manufacturers (OEMs) adopted air-cooled batteries but as performance and safety protection demands increased, they have moved towards more efficient water-glycol cooling systems.
Air-cooling didn’t sufficiently keep the battery within its most effective operating temperatures, between 20 to 40 degrees Celsius. The results were loss of range, and in some instances often catastrophic battery failures, leading to the destruction of vehicles and potentially their surroundings.
A safer alternative was clearly needed. That’s when most OEMs turned to the technology that they mastered from the production of ICE vehicles: a water-glycol mix which, in this case, is pumped and circulated through the battery pack using a series of tubes or cold plates.
Better, But Still Not Ideal
External cooling mechanisms like water-glycol mixes symbolized a major step forward in the cooling of EV batteries, E-motors and other Power electronics. These systems and fluids keep the batteries at suitable operating temperatures and help extend both the range and life of the battery.
Despite their undeniable advantages, water-glycol mixes also have some downsides. For one, they can’t come directly into contact with the battery itself because water and electricity aren’t compatible. Water leaking from the cold plate or tubing could come into contact with electronics, leading to safety issues.
Secondarily, thermal runaway occurs when the heat isn’t dissipated properly within a battery pack, causing the battery to deteriorate. Unless the battery is cooled effectively, the temperature within the battery will continue to rise and cause current to increase. As the situation continues, the temperature of surrounding batteries will rise and current will increase which could lead to an uncontrolled battery fire.
These are two of the reasons OEMs are currently working with partners to research alternatives to water-glycol cooling methods. One of the most promising solutions can be found in immersion cooling.
The Emerging Immersion Cooling Solution
Though not in commercial production yet, OEMs are exploring how immersion cooling can enhance their EV battery systems. Immersion cooling allows a battery to be submerged in dielectric fluids, allowing more direct cooling than a water-glycol system.
This system has two significant safety advantages over the water-glycol system. First, the fluid surrounds the battery cells directly, which allows immediate cooling in the case of a fire. This prevents a fire in one cell from spreading quickly to another and causing complete destruction of the entire battery module and pack. Secondly, the fluid itself is not flammable and therefore doesn’t contribute to the potential fire hazard.
The safety goals of immersion cooling are threefold:
- Prevent battery degradation due to unexpected cell aging
- Cool the battery cells quickly and reduce the chances of thermal runaway occurring through effective heat dissipation
- Containment: Should thermal runaway occur in one cell, the fluid will prevent it from propagating to adjacent cells and avoid a cascade effect spreading within the entire battery pack
Crucially, immersion-cooled batteries can pass nail penetration safety tests. Dielectric oils prevent electrical shorts even if a fluid leak occurs. While China is currently the only country requiring EVs to pass nail penetration tests, it is expected that they will eventually become standard around the world, making immersion cooling systems the logical choice in all new EVs.
Lastly, high-speed charging will become increasingly important as more EVs come into the market. Immersion cooling offers significant gains in safety in high-speed charging scenarios which will bring consumers peace of mind, enabling more rapid adoption of EVs.
As EV OEMs begin implementing immersion cooling systems as early as 2025, they will be looking for partners to work in tandem to create the fluids necessary to make the systems work. These partners are expanding, or will need to expand, their testing capabilities to address the new challenges of EVs. By identifying key failure modes, systems and fluid tests aimed at creating a safer environment now, experienced fluid manufacturers will be ready to meet the moment.
For more information on immersion cooling, contact us or visit the Electrification section of Lubrizol360.