All electronic devices and electrical structures generate heat – from a simple circuit to a mobile phone to an electric vehicle. This heat can be controlled using thermal management, typically a cooling system or heat pump, which decreases the system's temperature to avoid premature failure and improve the device's reliability.
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Recent reports of battery packs in electric vehicles (EVs) bursting into flames and smartphones overheating have highlighted the need for effective thermal management. Many industries and material suppliers are taking this into account in product design and material choice.
Managing Flaming EVs
The future of the automotive industry is electric. Developers constantly strive to improve by increasing battery capacity, range, charging rates, wide bandgap semiconductors, and high-performance traction motors.
However, tens of thousands of EVs were recalled in 2020 due to battery fires. Although relatively uncommon, EV fires are more severe and still represent the unknown. Every OEM has experienced at least one serious fire-related incident; sometimes, cell contaminants are blamed, others on poor thermal design, which led to batteries overheating.
Whatever the cause, their occurrence has highlighted the importance of preventing cell overheating as well as detecting and containing thermal runaway – all of which demand improved thermal management systems, solutions, and materials.
Faster charging is a key topic in the EV market - range anxiety becomes less of an issue if battery charging takes 30 minutes. However, this presents a new problem. Higher voltage batteries enable faster charging but need to be kept cool throughout the process to prevent thermal runaway and preserve the longevity of the cells.
Immersion cooling could solve this problem. Initially used in IT, this novel technology involves submerging a device in a thermally conductive dielectric liquid or coolant circulated around hot components and cool heat exchangers to remove excess heat.
Power electronics – particularly the main inverter – also require cooling. Most manufacturers use silicon insulated-gate bipolar transistors (Si IGBT), which generate a significant amount of heat but are being replaced with silicon carbide metal-oxide-semiconductor field-effect transistors (SiC MOSFET).
While these can decrease the footprint of the package and increase the power density, they present a more significant challenge in heat dissipation.
Many electric motors use permanent magnet-based traction systems that denature at high temperatures, even those that don't need cooling to preserve performance and lifecycle. Manufacturers have transitioned from passive cooling or with forced air towards water glycol systems.
Liquid-cooled batteries were the most popular form of battery cooling in 2019, a continuing trend with manufacturers such as Nissan, Honda, and Porsche adopting such methods. Nissan was the first to use the idea in 2013, with almost every EV model regardless of the manufacturer now including the technology.
Speedy Phones Pose Fire Risk
Faster downloads and better connections are crucial to today's increasingly complex and connected world but come at a cost – overheating smartphones. The first 5G phones, which emerged in 2019, often switched back to 4G when things became too hot. There were also difficulties with signal propagation, as many of the materials struggled with the mmWave range necessary for high-speed communications.
Thermal interface materials (TIMs), heat spreaders, and thermal insulation materials were sometimes replaced with vapor chambers to improve heat dissipation. Although, many manufacturers still alternated between these and graphite heat spreaders, which are cheaper, lighter, and less complex.
In 2020, several new thermal materials for 5G applications emerged, including thermal gels to replace TIMs, and a new thermal insulation material with thermal conductivity less than air, reducing hot spots on the device surface.
It is not just EVs and smartphones that need thermal management materials, so does the aerospace industry. Recent acquisitions will allow companies such as Nevada-based Rocky Research (acquired by Honeywell) to explore new opportunities.
At the same time, a partnership between Airbus and KULR Technology Group will focus on passive propagation resistant battery design solutions for lithium-ion batteries in aerospace applications.
The cost of recalling thousands of cars or smartphones not only costs millions, but it is also damaging to the company's reputation. The fact that manufacturers are including thermal management materials within their products, whether a heat pump or a liquid-cooled system in an EV or vapor chambers and thermal gels in a mobile phone, shows a growing recognition of the problem. Their desire to improve safety for consumers is clear.
References and Further Reading
Edmonson, J., et al. (2021) Thermal Management for Electric Vehicles 2021-2031. IDTechEx. Available at: https://www.idtechex.com/en/research-report/thermal-management-for-electric-vehicles-2021-2031/822. Accessed 9th August 2021.
Edmonson, J. (2021) Thermal Management In 2020; Highlights from IDTechEx. IDTechEx. Available at: https://www.idtechex.com/en/research-article/thermal-management-in-2020-highlights-from-idtechex/22373. Accessed 9th August 2021.
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