Some of the biggest hurdles to widespread adoption of electric vehicles are range anxiety, battery longevity and safety. As the electric vehicle market grows, and for it to reach its full potential, there is an increased need for effective thermal management of the vehicles. Keeping heat under control leads to improved charging, performance, range, longevity and safety. A new report from IDTechEx covers several aspects of thermal management for electric vehicles, including batteries, motors and power electronics.
There have been several high-profile, battery-related fires from well-known automotive manufacturers and in stationary energy storage from South Korea. This does little to instill confidence in potential consumers. With this in mind, several new regulations have been proposed relating to safety aspects unique to electric vehicles, the likely outcome of this being that manufacturers will be required to halt thermal runaway at the individual cell level and warn vehicle occupants, giving them at least five minutes to exit the vehicle once a thermal event occurs. Several factors must be considered when designing an electric vehicle for safety, from the materials used in the battery pack construction to thermal runaway prevention and early detection. Several companies are designing methods of stopping thermal runaway between cells, including flame-retardant encapsulants, interweaved products and phase change materials. Effectively dissipating heat from the battery module or pack to a heat sink is also important and usually carried out using a thermal interface material. This is another area where manufacturers have adopted several strategies including gap pads, fillers and conductive adhesives.
Every manufacturer has their own methodology to thermally manage their batteries, with no clear consensus on the most effective design. Companies like Tesla are set on their patented water-glycol coolant lines which “snake” their way between the cylindrical cells in the pack, whereas OEMs like Nissan and Toyota are committed to air cooling. Active cooling of batteries with fluids allows the vehicle to be kept cool in conditions where the vehicle is stationary but the batteries are in high demand, like during fast charging. This also allows the batteries to be raised to optimal temperature in cold ambient conditions. These are significant advantages but come at the expense of weight, complexity and cost. In addition to the more widely adopted technologies, there are other emerging alternatives such as immersion cooling and phase change materials. These technologies are gaining modest traction, especially for more specialized markets. The report appraises all these methods of cooling, in addition to the players utilizing them.
An electric motor is the unifying component of an electric vehicle and more demand is being put on them for high performance during extended use. The motor itself may not pose as much of a safety risk as the batteries, but the majority of manufacturers use motors containing permanent magnets that can be denatured and rendered useless above a critical temperature and so also need effective thermal management. Even motors without these permanent magnets are still required to be kept cool to improve performance and reduce the risk of overheating neighboring components. The methodologies adopted typically consist of air, oil or water-glycol cooling; several manufacturers utilize the same coolant circuit for their batteries and motors, in doing the number of components and fluids are reduced whilst simultaneously allowing for the utilization of excess motor heat to warm the batteries or passenger cabin in cold ambient conditions.
In addition to the batteries and motors, the power electronics also have to deal with significant heat, especially with the trend towards operating at higher power densities and temperatures. The way in which wire bonds and soldering is carried out as well as the material used makes a big impact on the performance and longevity of the power electronics. Several OEMs are also shifting towards using advanced substrates and even eliminating the thermal interface material altogether.
The report from IDTechEx covers all these points through extensive research including primary interviews from companies in the field. The report covers the strategies used by major OEMs, emerging technologies and market forecasts for electric vehicles and their thermal management technologies. ◊