Lithium-ion batteries are generally used in electric cars. A major disadvantage of these batteries is the relatively long charging time, which means that electric cars soon need several hours to fully charge. An alternative that can be charged faster are supercapacitors, which, due to their relatively low energy density, are as yet less suitable for electric cars. A development by the UK's University of Surrey and the University of Bristol in collaboration with the company Superdielectrics could change this.
Lithium-ion batteries are popular mainly because of their high energy density and are used in a variety of devices. These include electric cars, but also smartphones and laptops. However, the batteries have significant drawbacks. For instance, batteries charge relatively slowly, should not be discharged too far, are relatively expensive and have a limited lifespan. Supercapacitors are an alternative to lithium-ion batteries and store energy using electrodes and electrolytes, which allow for rapid storage and release of energy. Supercapacitors can therefore be charged and discharged a large number of times without losing capacity. This charging and discharging process is also extremely fast.
Low energy density per kilogram
However, the current generation of supercapacitors has a relatively low energy density, which is about one-twentieth that of lithium-ion batteries. This ensures that, despite their ability to be charged and discharged quickly, supercapacitors are not currently a viable alternative to lithium-ion batteries. Incidentally, despite these limitations, the technology is already being used in city buses in China. However, these buses have to be recharged at almost every bus stop due to the low energy density of supercapacitors.
The two UK universities and Superdielectrics announced last year they had developed new polymeric materials with dielectric properties 1,000 to 10,000 times greater than existing electrical conductors. The researchers now report using these materials to have succeeded in developing supercapacitors with a significantly higher energy density. This higher energy density means that supercapacitors can now be an interesting alternative to lithium-ion batteries and could be used in electric vehicles and other applications in the future.
180 watt-hours per kilogram
For example, by combining the polymer they developed with a low-cost metal electrode film, the researchers managed to achieve a capacity of 4F/cm2. By combining the polymeric material with stainless steel electrodes that received special treatment, the capacity could even be increased to 11 to 20F/cm2. Details about these electrodes are being kept secret by the researchers for now due to a patent application. By comparison, existing supercapacitors typically offer a capacity of 0.3F/cm2. The researchers expect that if this capacity can be achieved in production, it will be possible to build supercapacitors with an energy density of 180 watt-hours per kilogram (whr/kg).
The researchers tested the new materials in two ways:
- by using small single-layer cells that are charged to 1.5 volts and used to drive small demonstration devices such as a fan
- by using a combination of three cells that are charged to five volts and light an LED lamp.
Research centres and production facility
So in these experiments, relatively small electrical devices were powered using the new supercapacitors. However, the researchers expect that the supercapacitors could eventually also be used in electric cars. Superdielectrics now has plans to set up a research centre and build production facility where the supercapacitors can be produced in small batches.
"These results are very exciting and it is hard to believe how far we have come in such a short time. We may be at the beginning of a new chapter in low energy storage technology that could shape the future of industry and society for many years to come," said Dr Brendan Howlin, a lecturer in Computational Chemistry at the University of Surrey.
Dr Donald Highgate, director of research at Superdielectric and an alumni of the University of Surrey, added: "If the current work can be put into production it promises to enable rapid charging of electric vehicles and provide a much-needed low-cost method of storing energy from renewable energy systems. Wind, wave and solar energy is available, but it is not constant. Without storage, it cannot be relied upon to meet our energy needs. This new work can provide an energy system transformation that supports our entire way of life - it is a development that is necessary to provide our children and us with a truly sustainable and environmentally friendly energy storage method."
Author: Wouter Hoeffnagel
Source: University of Surrey
Source: University of Bristol
Source photo: Pixabay/ paulbr75
