Thermal management continues to be a key topic for electric vehicle (EV) design. Early trends in the market largely revolved around the adoption of active cooling for the battery pack, now this is the industry standard.
However, batteries, motors, and power electronics in EVs continue to evolve with developments of cell-to-pack designs, directly oil-cooled motors, and silicon carbide power electronics being just a few of the key trends that will impact thermal management strategies across the key driveline components in an EV.
As the thermal management market evolves, opportunities arise for materials companies, component suppliers, vehicle designers, and other players in the rapidly growing EV industry.
This report from IDTechEx analyses the EV market and the thermal management strategies adopted by OEMs and their suppliers, with a look to the future and how key EV technology trends will impact these methods for electric vehicle batteries, motors, power electronics, and charging infrastructure. This information is obtained from primary and secondary sources across the EV industry.
The research also utilises IDTechEx’s extensive electric car database that consists of over 450 model variants with their sales figures for 2015-2022H1 plus technical specifications such as battery capacity, battery thermal strategy, motor power, motor cooling strategy, and many others. Market shares are given for existing thermal management strategies (air, oil, water, immersion) for the battery, motor, and inverter in EVs along with market forecasts to 2033.
Battery: cell-to-pack, coolants, thermal interface materials, and fire protection
The key factors for EV battery development are increasing energy density and reducing costs. This has been made more difficult with supply chain shortages, but battery designs are becoming simpler as designers start to remove materials that are not the cells. This strategy culminates in cell-to-pack or cell-to-body designs.
Cell-to-pack eliminates strict module housings in favour of having all of the cells stacked together. Cell-to-body makes the battery a structural part of the vehicle. Designs from BYD, Tesla, and others have made it on to the road, with further announced designs coming to market in the near future. With the removal of so much from the pack, how does this impact thermal management?
Some active cooling strategies will remain similar, with a large cold plate beneath or above the cells, albeit now in contact directly with cells rather than their module housing. This minor change has a severe impact on thermal interface material (TIM) utilisation pushing in favour of thermally conductive adhesives to make a structural connection rather than the typical gap filler seen in many existing designs. This report forecasts TIM demand for EV batteries to 2023 in terms of mass and revenue, segmented by gap pad, gap filler, and thermally conductive adhesive.
As materials are removed from the pack, one might ask how fire safety is impacted? Removing module housings also removes a potential containment opportunity and several surfaces for fire protection. Many material suppliers are now tailoring their materials to provide multiple functions, including fire protection.
This enables fire protection to be included without severely impacting energy density of the pack. These include inter-cell materials that provide compression, thermal insulation, and fire protection as examples. This report gives an overview of some of the material options with a total forecast to 2033. For a segmented material forecast and deeper dive into fire protection, please see the Fire Protection Materials for EVs report by IDTechEx.
The transition to active liquid battery cooling has happened quicker than many, including IDTechEx, had originally predicted. In the first half of 2022, over 70% of the electric car market was using liquid cooling. The benefits of greater thermal performance and integration with the whole vehicle’s thermal management system have outweighed the reduced complexity of air cooling.
However, within this, we have seen a greater adoption of refrigerant cold plate cooling, gaining 6.5% greater market share in 2022 over 2021. Whilst typical automotive coolants and refrigerants have been used to date, there is gathering interest in tailoring these coolants to EVs, with lower electrical conductivity as one of the new features. This report forecasts the adoption of air, liquid, refrigerant, and immersion cooling for EV batteries in terms of kWh cooled by each method.
Thermal management trends vary by region. Liquid cooling gained dominance at the expense of air cooling. Source: IDTechEx
Motors
For electric motors, the magnets used in the rotor and the windings used in the stator must be kept in an optimal operating temperature window to avoid damage or inefficient operation. Water-glycol used in a jacket around the motor has been the standard thermal management strategy for electric motors in EVs.
However, recent years have seen much greater adoption of directly oil cooling the motor to provide better thermal performance, and in some cases, eliminate the cooling jacket, reducing the overall motor size. Oil cooling became the dominant form of cooling for EV motors in the first half of 2022, but that’s not to say that water-jackets are going away, they are often used in conjunction with oil cooling, and water-glycol coolant is typically used to remove heat from the oil and can be used to integrate with the vehicles thermal management strategy as a whole. IDTechEx provides a 10 year forecast of electric motors segmented by the use of air, oil, or water-glycol cooling.
Permanent magnet motors have remained the dominant motor type in 2022. Source: IDTechEx
Power electronics
The adoption of SiC is the largest trend in the news for EV power electronics and with good justification. The EV market provides a huge addressable market for adoption of the wide bandgap semiconductor to enable higher system efficiencies. This has had an impact on the construction of power electronics packages.
Developments are happening for wire bonding, die-attach, and substrate materials, largely with the goal of improving package reliability, especially for wide bandgap semiconductor modules. Many inverter suppliers have now eliminated the TIM between the heatsink and baseplate to improve thermal resistance, although this does not mean there are no TIM opportunities within power electronics.
Many components still require a TIM and TIMs are often still used to bond the module heat sink to the water-glycol cold plates. The report provides analysis of these trends and the drivers behind adoption.
Inverter IGBT or SiC MOSFET modules are mostly cooled using water-glycol. However, both single-side and double-sided cooling options are used, each with their own benefits. There has also been an increase in using oil to cool power electronics to eliminate much of the water-glycol componentry within the electric drive unit, using the same oil for the motors and inverter. Whilst there has not been adoption of this approach in the current market, IDTechEx sees promise for this approach and includes a 10-year forecast for EV inverters using air, water, or oil cooling.
