A research team led by Professor Dan Li of the Department of Materials Engineering at Monash University in Australia has developed a completely new strategy to engineer graphene-based supercapacitors. The 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.
The research has been published in Science. The graphene-based supercapacitors (SC) should be 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 just seconds, the principle 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 liter means SCs are unfeasibly large or must be re-charged frequently.
Energy density is a huge problem for capacitors. But hold on – Professor Li’s team has created an SC with energy density of 60 Watt-hours per liter – comparable to common lead-acid batteries and around 12 times higher than commercially available SCs.
Now that is something worth major attention. We’re talking volume, not weight.
Professor Li sets up the point of the research effort, “It has long been a challenge to make SCs smaller, lighter and compact to meet the increasingly demanding needs of many commercial uses.”
Graphene is formed when graphite is broken down into layers one atom thick and 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 instead control the spacing between graphene sheets on the sub-nanometer 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 in Professor Li’s electrode is maximized 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 easily and cost-effectively be 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.
This looks like a major breakthrough. SCs just haven’t been able to compete with batteries on the space needed to accommodate them. Li’s technique of taking advantage of chemically converted graphene’s intrinsic micro-corrugated two-dimensional configuration and self-assembly behavior, and then using capillary compression to form the graphene gels with the electrolyte to make the capacitor is a fine example of innovative and creative thinking.
For everyone in the electrical storage business, the Monash team has certainly taken the brass ring for now.