Thermal management of electric vehicles: The focus is on batteries but motors and power electronics follow
The battery deserves the main focus when it comes to developing technology in electric vehicles. But the electric car's powertrain must work fully to perform optimally and interact with the passenger cabin air conditioning system. This means that thermal management of the motors, power electronics and how it all interacts is just as important as the battery.
The early trend of the electric vehicle market was away from passively cooled or forced air-cooled batteries toward liquid cooling through cold plates and cooling ducts. This shift is almost complete, with IDTechEx finding that 95% of the EV market has adopted cold plate cooling (water or radiator) in the first half of 2023. The next stage of development is around battery integration, with cell to pack. Cell-to-body type designs are becoming increasingly popular. This typically involves cells with a larger form factor and somewhat reduces the complexity of the cold plate design. For example, BYD's Blade battery requires one large cooling plate for the entire package. The Tesla 4680 package requires fewer cooling channels to cool the sidewall cells thanks to the use of fewer individual cells in the package.
Air-cooled batteries dominated the early electric vehicle market. In 2023, this approach is almost out of the market. Source: IDTechEx
This also profoundly affects the use of thermal interface material (TIM). First, there is less per compound, but since the cells can be attached directly to the cold plate, the TIM should provide greater adhesion properties. IDTechEx research found that despite the lower quantity of TIM, the price of the thermally conductive adhesive is higher than that of a typical gap filler, meaning similar revenues per vehicle can be obtained for TIM suppliers. Combining this with the growing electric vehicle market, IDTechEx expects a 5.6 times increase in TIM's annual revenues by 2033 compared to 2022.
Cell-to-package/body deployment is still at an early stage, with IDTechEx estimating that approximately 15% of the EV market will use a cell-to-package or cell-to-body design in 2022. The market is somewhat divided on development, with larger players focusing The Chinese and Tesla in the US have focused heavily on cell-to-package integration and increasing integration, while some players have taken a modular approach, such as General Motors with its Ultium platform, which can help with servicing.
Electric motors present a different heat management challenge; While water jackets around the engine have been common, the trend is toward engines that use oil inside them. This allows for more direct contact between the coolant and the motor coils but also a smaller overall motor if the housing is removed. Oil-cooled engines overtook water-cooled engines in 2022, with growth continuing into 2023, with estimates for the first half of 2023 approaching 65% of the market. IDTechEx expects both approaches to remain but with oil cooling controlling the majority for the future of the market, especially for higher cost/performance models.
As engines move to direct oil cooling, could the same thing happen for power electronics? The adoption of silicon carbide power electronics results in greater heat flux in MOSFETs (over silicon IGBTs) thanks to higher power density. Typically, the inverter and motor are housed together in the drive unit, with the same water loop cooling both components. There has been some interest in cooling the inverter chips directly with oil as well, to provide better thermal contact, but this would also remove the water circuit from the drive unit. Thus a single water/oil heat exchanger can be used to communicate the vehicle's thermal system with the drive unit. The SingleOilCnL project between Dana, Diabatix, Lubrizol, Siemens and Flanders Make explores this idea. IDTechEx believes this is a promising approach but is unlikely to become a mainstream solution in the near future. However, with increased adoption of SiC power electronics and more highly integrated drives, we could start to see some examples later this decade.
What can be done to mitigate EV fires?
Concerns about EV fires remain at the forefront of the EV industry, and now more than ever, in the public eye. The automotive market has seen major recalls related to battery fire risks from automakers such as General Motors, Hyundai, Volkswagen, and many others. More and more data has been published suggesting that electric vehicles have a much lower risk of fire than combustion engine powered vehicles, although it should be noted that the data at this stage does not take into account factors such as the age of the vehicles. The market has taken several steps overall to combat the potential for EV fires, such as more stable chemistry, increased battery quality control, and improved software management.
Regardless of how often they occur, EV fires can be extremely destructive and very different from their combustion engine counterparts. The combination of volatile chemicals and a thermal escape mechanism can make fires explosive and difficult to extinguish. This is one of the main drivers behind IDTechEx's forecast that the demand for fire protection materials in electric vehicles will grow 13 times by 2033 compared to 2022.
Despite the focus, regulations have evolved rather slowly. China was the first country (01/01/2021) to impose a 5-minute warning between a thermal event and fire or smoke exiting the package, allowing occupants to exit the vehicle. Other regions have had draft regulations in the works for several years, but these regions often struggle to keep up with the rate of development of technology in the field. UN GTR Regulation 20 appears to include similar escape times but also adds features such as testing for the risk of gas release while the vehicle is running or off. However, the details of the regulation will certainly increase pressure on OEMs to provide spread mitigation and detection methods along with comprehensive fire protection.
There are several materials that can provide thermal runaway protection in a battery pack. In general, and especially with more energy-dense battery designs, these materials must provide multiple functions, including thermal insulation, fire protection, electrical insulation, and mechanical support for the cell. The market to date has largely used materials such as mica sheets or ceramic blankets at the unit/package level to provide electrical insulation and fire protection; This was often the case even before the advent of regulations and increased awareness of EV fires. When Tesla first launched the Model 3, it shifted toward using encapsulating agents around its cells to eliminate oxygen inside the package and add fire protection. The variety in battery designs and the need to keep weight and cost low makes manufacturers consider several options.
Comparison of properties of different fire protection materials for electric vehicles. Source: IDTechEx
One material that has seen rapid growth in the market is airgel. Aerogels provide excellent thermal insulation with minimal weight, but extreme temperature protection and high cost have historically limited their uptake. The IDTechEx report “Aerogels 2024-2034” found that the total aerogel market in 2020 was less than US$300 million, with less than 10% of that amount represented by the electric vehicle market. In 2022, the application of aerogels within electric vehicle battery packs will become a US$150 million market in its own right. IDTechEx expects airgel to become a standard option in this application, along with many other material options.
Thermal management of data centers
Over the past 17 years, GPU thermal design power (TDP) has quadrupled. The growing demand for cloud computing, cryptocurrency mining, and artificial intelligence indicates that the TDP of chips will continue to rise. In 2023, there will already be chipsets with a TDP close to 1000W. This trend presents significant challenges to the thermal management of data centers. Traditional air coolers that use fan walls and air conditioning run into trouble when the TDP exceeds 500 watts. As a solution, liquid cooling emerged, which includes direct-to-chip cooling and immersion cooling. Direct-to-chip cooling significantly enhances cooling capacity and can be relatively easily integrated into existing air-cooled data centers, facilitating a gradual transition for end users.
IDTechEx observed industry collaboration between liquid cooling solution providers and critical supply chain components, including chip manufacturers (Intel, AMD, Nvidia, Broadcom), server manufacturers (Dell, Gigabyte, Lenovo, Inspur, Hewlett Packard Enterprise), system/infrastructure integrators (Vertiv, Schneider Electric) and end users For data centers like Meta, Microsoft, and Verizon. Backed by technology giants, IDTechEx expects the data center liquid cooling market to exceed US$900 million by 2033.
Benchmarking between direct-to-chip cooling and immersion cooling: single-stage and two-stage. Source: IDTechEx
Immersive cooling opportunities: electric vehicles and data centers
Currently, immersion cooling for data centers is still in its infancy due to limited demand, successful cases and industry experience. However, IDTechEx has observed notable pilot projects led by major companies. In 2021, Microsoft presented pilot projects using two-stage immersion cooling for Azure cloud services. Being the first cloud provider to use two-stage immersion cooling in a production environment, Microsoft intends to continue using it in the long term. Similar trends occur with other players; For example, Meta has partnered with Iceotope to move standard high-density storage from air-cooled to single-phase immersion cooling in 2022. Additionally, Minerbase, a leading cryptocurrency mining solutions provider, launched a flood-cooled data center in May 2023.
While discussions regarding fluid costs and PFAS regulations continue, IDTechEx believes that applications requiring high-performance computing are likely to adopt submerged cooling more quickly, opening significant market opportunities for refrigerant suppliers, device manufacturers, end users and other entities within the supply chain. . The IDTechEx report “Data Center Thermal Management 2023-2033: Technologies, Markets, and Opportunities” finds that annual revenues for the data center immersion cooling industry will triple between 2022 and 2033.
Flooding cooling is also receiving significant attention for electric vehicle batteries. While immersion can provide greater thermal uniformity for cells and eliminate cold plates and TIMs, it has some major challenges that prevent its greater adoption. The first is the increased fluid pumping pressure required due to the decreased thermal conductivity of the fluid. The second is the additional spacing required between cells for fluid flow. There is also the challenge of effectively sealing the batteries to avoid leaks.
There are several examples of high-performance or high-cost electric vehicles that are using or planning to use immersion cooling, such as Mercedes-AMG and McLaren. There are also partnerships between technology developers and chiller suppliers, but for the reasons outlined above, IDTechEx expects that immersion cooling will be largely limited to applications that require energy-dense but not energy-intensive battery packs. Despite this, a small portion of the growing EV market is still significant, with the IDTechEx report “Thermal Management for EVs 2023-2033” predicting an 8-fold increase in fluid demand between 2022 and 2027 across EV segments.
IDTechEx offers a number of in-depth research reports on thermal management, and all of the expert-led data and analysis on this topic is available as part of a Market Intelligence subscription. For more information please visit www.IDTechEx.com.
This article is taken from 'Technology Innovations Outlook 2024-2034', a free magazine containing articles written by analysts by IDTechEx that provide insights into a number of areas of technology innovation, assessing the landscape now and giving you forecasts for the next decade. You can read the entire magazine at www.IDTechEx.com/Magazine.
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