A new lead-free, high temperature ceramic capacitor developed by scientists at the National Physical Laboratory (NPL), UK could improve the efficiency and reliability of electric and hybrid vehicles by enabling the removal of heavy complex cooling systems.
“Electric vehicle operating temperatures can go up to 140°C [almost double the temperature conventional capacitors can withstand] and even higher in some cases,” Tatiana Correia, lead researcher on the project, told The Engineer in an interview. “To compensate for that, the power electronics are covered by a complex cooling system that brings extra weight, and that [affects] the energy consumption and mileage range of electric vehicles as well.”
“A lot of manufacturers are looking at getting rid of [the weight] of active cooling—pumping water around—and instead just blowing air over it,” Billy Wu, a PhD student at Imperial College London’s Energy Futures Lab who is unconnected with the NPL research, told The Engineer. But, there’s only a certain amount of heat you can remove through convection in the air.”
“Cooling systems add extra mass and extra power losses because you need to power [the] pumps. So, anything you can do to minimize the heat that you generate adds to the lifetime and range of electric vehicles,” he added.
NPL researchers claim their new material, called HITECA (High Temperature Capacitor), can hold more energy and function at much higher temperatures—over 200°C—than conventional capacitors. HITECA is made from a ceramic paste with a granular stucture comprising a bismuth ferrite (BiFeO3) compound doped with strontium-titanate (SrTiO3). According to Correia, only one scientific paper had been published previously on a version of this material, so the researchers, after experimenting with a range of other substances, began working with its composition to adjust it for use in capacitors.
“It’s very difficult to increase energy density in these kinds of ceramic materials. So we have to tailor the composition, we need to change the structure, the lattice and the doping,” she said. “The main difficulty of these materials is that they can store quite a lot [of energy] but they can’t release it. So, we introduced some strontium-titanate and other dopants to reduce the remnant energy.”
The NPL research team is now looking to test the capacitor technology in an electric vehicle power electronics system, and believes the new capacitor could be used for other systems that involve power conversion under extreme conditions, including in photovoltaic solar, space, or oil and gas technology.
“Industrial electronics need to be able to perform in the harsh environments in which they operate. The ability of HITECA capacitors to function at higher temperatures than existing capacitors will help make electronic systems more robust and remove barriers for technologies such as electric vehicles that rely on them,” Correia said.
The project was funded by the Technology Strategy Board program for Low Carbon Vehicles. Partners included Queens University of Belfast, Queen Mary, University of London; capacitor firm Syfer, material processing company Nanoforce Technology and French automotive component manufacturer Valeo. NPL currently holds a patent for HITECA.