A breakthrough in graphene research could pave the way for a compact supercapacitor that lasts as long as a conventional battery.
Supercapacitors are generally made of highly porous carbon impregnated with a liquid electrolyte to transport the electrical charge and have long held promise for energy storage applications due to their almost indefinite lifespan and the ability to re-charge in seconds.
But their low-energy density – a measure of their energy-storage-to-volume ratio – of five to eight Watt-hours per litre, has meant they are unfeasibly large or must be re-charged frequently.
Now engineers at Monash University in Australia have created a new strategy to engineer graphene-based supercapacitors with an energy density of 60 Watt-hours per litre – comparable to lead-acid batteries and around 12 times higher than commercially available supercapacitors.
The breakthrough could make supercapacitors viable for widespread use in renewable energy storage, portable electronics and electric vehicles.
"It has long been a challenge to make supercapacitors smaller, lighter and compact to meet the increasingly demanding needs of many commercial uses," said Professor Dan Li of the Department of Materials Engineering, who led the team.
Research published today in the journal Science explains how Li's team exploited an adaptive graphene gel film they had developed previously, rather than the “hard” porous carbon traditionally used in supercapacitors.
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.
The team used liquid electrolytes – generally the conductor in traditional supercapacitors – to control the spacing between graphene sheets on the sub-nanometre scale meaning the electrolytes fulfilled a dual function of maintaining the minute space between the graphene sheets as well as conducting electricity.
In traditional “hard” porous carbon space is wasted with unnecessarily large pores, but in Prof Li's electrode density is maximised without compromising porosity.
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," Prof Li said.
The work was supported by the Australian Research Council.