Monash researchers have developed a completely new strategy to engineer graphene-based supercapacitors (SC) with the energy density of lead batteries, making them viable for widespread use in renewable energy storage, portable electronics and electric vehicles. The energy density of 60 Watt-hours per litre – comparable to lead-acid batteries and around 12 times higher than commercially available SCs.
Porous yet densely packed carbon electrodes with high ion-accessible surface area and low ion transport resistance are crucial to the realization of high-density electrochemical capacitive energy storage but have proved to be very challenging to produce. Taking advantage of chemically converted graphene’s intrinsic microcorrugated two-dimensional configuration and self-assembly behavior, we show that such materials can be readily formed by capillary compression of adaptive graphene gel films in the presence of a nonvolatile liquid electrolyte. This simple soft approach enables subnanometer scale integration of graphene sheets with electrolytes to form highly compact carbon electrodes with a continuous ion transport network. Electrochemical capacitors based on the resulting films can obtain volumetric energy densities approaching 60 watt-hours per liter.
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.