The capacitor, called HITECA, can operate close to normal efficiency at over 200°C, significantly higher than any other capacitor on the market. It also offers a high energy density of 18.6 J/cm3 at 972 kV/cm.
“The opportunities for electric vehicles are huge, both financially and environmentally, but they are currently being held back by a few technical issues. With this high temperature capacitor we believe we have solved an important one of those issues and will play a vital part in the move towards mass market electric vehicles,” said Tatiana Correia, lead scientist on the project.
"At the moment the prototype is designed for a capacitance of 100 nF and rated for 1000 V, but these values ought to be tailored by the geometry and design, which will depend on the application," she said. "The designs are standard for a multilayer capacitor, but in terms of the energy density the important part is the capacitance at the operating voltage, and there is where HITECA capacitor has a major benefit as it shows much lower voltage coefficient of capacitance than other ceramic-capacitors in the market."
To develop the capacitor, NPL investigated a range of lead-free materials that could have the desired properties to develop into a high temperature capacitor. The scientists explored different compositions and different ways of fabricating them. They measured current at a range of high temperatures using advanced measurement techniques. The most promising materials were optimised to achieve the desired properties. The resulting capacitor is created from a ceramic, based on doped-BiFeO3 compound.
Current capacitors do not meet the EV requirements due to an inability to function reliably under the high temperatures created in electric vehicles says NPL and the researchers have overcome this issue as part of a project backed by the UK's Technology Strategy Board funded project.
The project has also allowed NPL to develop a range of new capabilities in metrology to assess energy and