'Soft' approach leads to revolutionary energy storage

'Soft' approach leads to
revolutionary energy storage
Credit: University of Manchester
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 today 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.
More information: "Liquid-Mediated
Dense Integration of Graphene
Materials for Compact Capacitive
Energy Storage" Science , 2013.
Provided by Monash University