13 July 2013
One of the big enemies of electric vehicle batteries is heat. Batteries already warm up under normal use, but when hot summer temperatures or high workloads are thrown in, overheating becomes a real possibility. According to the Fraunhofer Institute for Environmental, Safety and Energy Technology, running a battery at ten degrees over its maximum “comfort level” of about 35ºC (95ºF) can deplete its service life by half. That’s why researchers there have developed a battery coolant known as CryoSolplus, which is said to offer three times the cooling capacity of plain water.
CryoSolplus consists of water, paraffin, stabilizing tensides (detergents) and “a dash” of glycol anti-freeze. When the solution is cool, the paraffin takes the form of solid droplets. The tensides keep those droplets suspended uniformly throughout the mixture, as opposed to clumping together or floating on top.
As the solution is heated, the droplets melt, storing the heat in the process. Circulated in pipes around EV batteries, CryoSolplus could utilize this process to continuously carry away battery-generated heat. The liquified paraffin forms back into droplets as the solution cools, ready to repeat the process on the next drive.
The even dispersion of the droplets is key to the coolant’s effectiveness, so the researchers had to make sure that the tensides they chose could be stored for a long time without deteriorating, that they could stand up to the rigors of being pumped through pipes, and that thermal stresses (such as freezing and thawing) wouldn’t affect their performance.
Because CryoSolplus conducts heat so much better than water, less liquid would be needed within a vehicle’s cooling system, resulting in a smaller coolant tank size and lower weight. It is estimated that a system using the coolant would only be about €50 to €100 (US$61- $122) more expensive than a water-based cooling system.
The company is now working on boosting the coolant’s heat capacity, along with its ability to transfer heat and flow more smoothly. Field tests using an experimental vehicle are being planned.