Nature: Super battery made from graphene
Better energy storage technologies are integral to developing more energy-efficient society, be it by smoothing the intermittent output of wind turbines, harnessing kinetic energy, or prolonging the performance of portable electronics.
Batteries, which store energy in electrochemical reactions, offer high-storage densities but are relatively slow when charging or discharging — limiting their use. Electrochemical capacitors or 'supercapacitors' store electrical charge at the interface between an electrode and an electrolyte. They are a much faster form of energy storage, but have considerably less capacity.
The more surface area, the greater the capacity to store energy. Graphene has two properties that make it the ideal material to make supercapacitors: exceptionally high surface area and the fastest electrical conductivity. In practice, however, the graphene sheets stick together, lowering the graphene electrode's functional surface area and hindering the technology.
Researchers at the University of California in Los Angeles have now demonstrated an electrochemical capacitor made of graphene, sheets of carbon one-atom thick, that can store as much energy as conventional batteries yet can be charged up to 1,000 times faster.
Maher El-Kady, a chemist at Cairo University in Egypt, and colleagues prepared graphene using standard laser-scribing technology more typically used to etch labels and images onto DVDs. The researchers covered a LightScribe-enabled DVD with a coat of graphite oxide. The infrared laser in the read/write head stripped stacked sheets of graphite oxide into well-exfoliated sheets of graphene. They then constructed a symmetric supercapacitor from two identical 'laser-scribed' graphene electrodes, an ion-porous separator and an electrolyte.
"Our initial calculations show that the whole process is viable for commercial applications," says El-Kady. "Our graphene electrodes can also be bent arbitrarily without any change in their electrical properties, so we have a dream device that stores enough energy to power portable electronics while being in line with the coming boom in flexible electronics such as plastic solar cells."