Australia’s Monash University researchers have brought next generation energy storage closer with an engineering first - a graphene-based device that is compact, yet lasts as long as a conventional battery.
Published in Science, a research team led by Professor Dan Li of the Department of Materials Engineering has developed a completely new strategy to engineer graphene-based supercapacitors (SC), making them viable for widespread use in renewable energy storage, portable electronics and electric vehicles.
SCs are generally made of highly porous carbon impregnated with a liquid electrolyte to transport the electrical charge. Known for their almost indefinite lifespan and the ability to re-charge in seconds, the drawback of existing SCs is their low energy-storage-to-volume ratio - known as energy density. Low energy density of five to eight Watt-hours per litre, means SCs are unfeasibly large or must be re-charged frequently.
Professor Li's team has created an SC with energy density of 60 Watt-hours per litre - comparable to lead-acid batteries and around 12 times higher than commercially available SCs.
"It has long been a challenge to make SCs smaller, lighter and compact to meet the increasingly demanding needs of many commercial uses," Professor Li said.
Graphene, which is formed when graphite is broken down into layers one atom thick, is very strong, chemically stable and an excellent conductor of electricity.
To make their uniquely compact electrode, Professor Li's team exploited an adaptive graphene gel film they had developed previously. They used liquid electrolytes - generally the conductor in traditional SCs - to control the spacing between graphene sheets on the sub-nanometre scale. In this way the liquid electrolyte played a dual role: maintaining the minute space between the graphene sheets and conducting electricity.
Unlike in traditional 'hard' porous carbon, where space is wasted with unnecessarily large 'pores', density is maximised without compromising porosity in Professor Li's electrode.
To create their material, the research team used a method similar to that used in traditional paper making, meaning the process could be easily and cost-effectively scaled up for industrial use.
"We have created a macroscopic graphene material that is a step beyond what has been achieved previously. It is almost at the stage of moving from the lab to commercial development," Professor Li said.
The work was supported by the Australian Research Council.
What is Graphene?
Graphene consists of a single layer of carbon atoms bonded together in a repeating pattern of hexagons, as shown in the Figure. Graphene is one million times thinner than paper; so thin that it is actually considered two dimensional.
Graphene’s flat honeycomb pattern provides several unusual characteristics, including the status of strongest material in the world. These single layers of carbon atoms provide the foundation for other important materials. Graphite — or pencil lead– is formed when you stack graphene. Carbon nanotubes, which are another emerging material, are made of rolled graphene that are used in bikes and tennis rackets.
Among its possible uses are the boosting of internet speeds, a touch sensitive coating, and the ability to extend the lives of computers. It is stronger than diamond and conducts electricity and heat better than any material ever discovered, and it will likely play an important role in many products and processes in the future. This material always had an economic appeal, in the 17th century for the the production of pencils, now in the 21st century as the next material of choice for high-end flexible electronics.