Scientists have found a new way to manipulate graphene to create a substance with record-breaking energy and power density.
When incorporated into energy storage devices called supercapacitors, this new form of graphene could be the key to high-capacity, fast-charging energy storage that could deliver power more quickly than conventional batteries, the researchers said in a statement.
The new material, called multiscale reduced graphene oxide (M-rGO), is created from graphite, a globally abundant resource. Researchers incorporated it into pouch cells, a type of rechargeable battery packaged into a thin, flexible, laminated foil envelope instead of rigid metal. The scientists published their findings Sept. 15 in the journal Nature Communications.
Pouch cells are used in electric vehicles, drones, wearable electronics, laptops, smartphones and tablets. Building them from M-rGO could lead to improvements in total capacity, charge time and the ability to power more complex and power-hungry devices with smaller batteries, according to the research team.
Soaking up power
Whereas traditional batteries store energy in chemical bonds, supercapacitors are electrochemical capacitors that store energy as separated electric charge on electrode surfaces. They have the advantage of superior energy density — how much energy can be stored in a given space — and power density — how quickly energy can be delivered per unit volume — over traditional batteries.
Until now, however, supercapacitors have been hamstrung by one significant limitation: only a portion of the potential energy storage of the materials from which they were created was available for use.
This limitation comes from graphene's physical makeup. While it has the advantage of allowing for denser electrodes — the solid conductors in a battery where charge is stored — it's very inefficient at using that space. Simply stacking graphene, for instance, is inefficient because the sheets adhere too closely together and don't leave enough space for the ions that need to move in and out to store energy.
To get around this problem, scientists built messy 3D structures similar to sponges, which provide both large amounts of storage area and pathways for ions to move. While lightweight, the downside is that these structures were large and cumbersome.
This breakthrough overcomes that issue by heating the graphene in a two-step process. This results in a tangled, curved graphene network with multiple levels of structure that still allows for the rapid movement of ions while providing lots of surface area for energy storage.
"This discovery could allow us to build fast-charging supercapacitors that store enough energy to replace batteries in many applications, and deliver it far more quickly," said Mainak Majumder, a professor of mechanical and aerospace engineering at Australia's Monash University, in the statement.
