Technology: Freudenberg develops thermally conductive elastomer for EVs

Weinheim, Germany – Freudenberg Sealing Technologies (FST) has developed a material which it says combines contrasting properties of conducting heat and electrical insulation.

The elastomeric material is currently undergoing initial testing for charging sockets, control units and batteries in electric cars, the company announced 21 July.

To develop the material, FST said its engineers used silicone rubber – rarely used in car manufacturing – as base material and combined it with "special fillers."

The product is intended for use primarily in electric car components, since semiconductors and other current-carrying elements are “never completely lossless,” FST said.

Any electrical energy that isn’t used for computing or switching becomes waste heat that must be dissipated into the ambient air or a cooling system. 

Electronic components may thus be mounted in thermally conductive aluminium housing, for example, which dissipates the heat either via cooling water or convection. 

According to FST, the heat conductivity can be reduced by roughness in material surfaces. 

When sprayed on a metal surface, the new FST material fills the gaps in rough surfaces, improving the heat transfer and enabling adhesion without additional surface treatments. 

“Our material retains its properties over a very high temperature range, from minus 50 to plus 250 degrees Centigrade, but it can be deformed with relatively low force,” said senior application manager Armin Striefler.

The product, according to Striefler, has a high dielectric strength of at least 20 kilovolts per millimeter. 

In addition, Freudenberg adds fillers made of special metal compounds to the material, increasing its heat conductivity from 0.2 to 1.5 to 2 watts per meter kelvin. 

According to Striefler, knowing how to combine and process the fillers with the base rubber is FST’s expertise.

The first series application for this new material class could be in the charging socket of electric vehicles. 

This is where car manufacturers face a challenge: To rule out possible malfunctions, the charging current must be monitored directly at the socket through continuous temperature measurements. 

However, the temperature sensors also have to be electrically shielded to prevent short circuits. 

As a solution, just like pin holders, the temperature sensors are overmoulded with FST’s thermally conductive silicone. 

In the same moulding press, the underlying connector plate is also moulded of standard thermoplastic to create a single mountable component. 

According to FST, the first prototypes for the charging socket with integrated sensors are already being tested by a car manufacturer.

The material can also be applied for the targeted cooling of control units, such as those used to switch the current between the battery and drivetrain of an electric vehicle. 

While the power electronics are cooled through the aluminium housing, the heat emitted by the electronic components generally radiates only into the air between the circuit board and housing wall. 

This is where, according to FST, the benefits of the silicone fully come into play.

The rubber can be produced as any three-dimensional moulded part, enabling direct contact between components, even if these components are usually positioned at different heights. 

This feature allows the heat flow to dissipate directly into the housing. An initial application in the battery control unit of a hybrid commercial vehicle is already being tested.

Freudenberg says its thermally conductive elastomers can also open up new opportunities for batteries, the core elements of every electric car. 

During rapid charging or when high performance is required while driving, the busbars used to connect battery modules and power electronics produce a relatively large amount of waste heat. 

Company engineers are now focusing on a module in which the thermally conductive silicone dissipates the waste heat from the busbars directly to the housing or a heat sink. 

This could reduce the conductor cross sections to such an extent that only about 50% of the normally used copper would be required. 

The “easy-to-install” module also includes the plastic carrier for the busbars overmoulded with the special silicone, in which the sockets for the screw connections are already integrated. The first functional prototypes are expected to be tested this year.

“We’re still in the beginning stages of applying the thermally conductive elastomers,” said Joachim Heinemann, technical director of special seals at Freudenberg Sealing Technologies. 

“But we can already see that the combination of thermal conductivity and electrical insulation has great potential to make future generations of electric cars more efficient.”