Thermal thinking

Hayley Everett

As the transition to electric vehicles continues, thermal interface materials are helping to improve the capability and safety of batteries

Thermal management solutions can be used across a range of industries but are becoming more prominent in the automotive industry as a result of a shift towards the production of electric vehicles. Consumers are demanding increased ranges and improved reliability from manufacturers, as the ban on petrol and diesel new car sales approaches. This shift towards electric vehicle adoption has brought about a focus on improving EV batteries, both in terms of capabilities and safety.

Thermal management

As these capabilities improve, thermal management becomes a challenge. This is because although thermal energy can be a positive feature when it comes to EVs – pre-heated battery cells can offer improved performance for example - excess heat poses significant safety risks. This is what concerns manufacturers most when developing improved battery capabilities as excess heat in one cell can easily spread to another if not managed properly. This thermal propagation can be prevented with the right thermal management solution, which involves the careful selection of materials during the design process.

More generally, excess thermal energy is a detrimental by-product that can deplete the service life of a battery, reduce performance and pose safety risks that can lead to ‘thermal runaway events’, including battery fires. In an ideal world, battery cells are maintained at an optimum temperature – this is what thermal interface materials (TIMs) try to support.

Exploring TIMs

TIMs help to maintain this optimum temperature in prismatic and pouch cell Li-ion batteries, by channelling and transferring heat, depending on the requirements of the manufacturer. They can come in solid or liquid formats and have thermodynamic properties that enable manufacturers to better regulate the transfer of heat by creating a multi-directional path for thermal transfer between components. This enables both heating and cooling, helping to improve vehicle performance, battery cell lifespan and vehicle safety.

The liquid system TIMs, often used as ‘gap fillers’, are electrically insulating, have a low density and help to reduce battery weight. They are robotically applied and are called ‘gap fillers’ because when there is a dissimilarity or ‘gap’ between a battery cell and a cooling interface, liquid TIMs flow and fill that space in a way that a gap pad can’t. This doesn’t make gap pads redundant though – both solutions are needed in the market.

Solid TIMs, which come in die cut conductive pads, are made of silicone and can be shaped for specific requirements. They have high dielectric properties, helping to withstand breakdown, suppress arcing and prevent electric conductivity, and offer extremely low out gassing at less than 70PPM. They have much higher thermal conductivity than gap filler liquids, up to 35 W/MK compared to a maximum of 6 W/MK.

Thermal interface materials can come in different configurations and formats, as the precise requirements vary from project to project and often require a partner with the capability to develop bespoke die cut solutions. TIMs are often selected based on considerations of thermal conductivity requirements, whether OEMs require heat to be contained through insulation or taken away via conduction and based on dielectric strength requirements. Material converter and engineering firm Tecman has expanded its automotive product range to include TIMs to meet these demands.

“The question isn’t ‘which solution is better?’ but ‘which solution is right for this specific project?’. Liquid and solid TIMs can both operate between -40C and 150C, but have different properties and roles,” says Kevin Porter, Technical Director at Tecman. “TIMs are helping manufacturers to manage thermal energy effectively and improve both the performance and safety of their battery components. By drawing on our extensive engineering and materials expertise, and deep understanding of e-mobility, we are able to engineer a thermal management solution that precisely meets specific requirements based on the properties of that material.”

Recent Issues