Advances in delivering and storing electricity are crucial to the future of electric cars and otherwise reducing reliance on energy produced from burning fossil fuels. Yet a powerful means of running electronics that can charge and discharge quickly while also storing large amounts of energy has long eluded scientists.
This predicament could be changing, thanks to new research. A team from the University of California, Los Angeles (UCLA), and Egypt's Cairo University describe in the March 16 issue of Science a new laser-based technique for making flexible, durable and highly conductive electrochemical capacitors—also known as ultracapacitors or supercapacitors—out of graphene. Electrochemical capacitors handle frequent charge/discharge cycles well but have been unable to store lots of energy. (Lithium-ion and other conventional batteries can store large amounts of energy but have short life cycles and are filled with hazardous chemicals known to catch fire under certain conditions.)
Electrochemical capacitors made using graphene—a one-atom-thick sliver of graphite—began showing potential to boost storage capacity a few years ago. Individual graphene sheets create a larger surface area than when they are stacked together as a piece of graphite. This larger surface area increases energy storage capacity. Yet the strong electrostatic attraction between graphene sheets makes graphene a difficult material to work with because it tends to cause them to stack back together into their original graphite form.
The researchers, led by UCLA Ph.D. candidate and Cairo lecturer Maher El-Kady and Richard Kaner, a professor in UCLA's Chemistry & Biochemistry and Material Sciences & Engineering departments, found a way to avoid this re-stacking. They covered an ordinary compact disk with a sheet of plastic, coated that plastic with graphite oxide and used a LightScribe DVD optical drive to locally heat the coating to turn it into a graphene film that can store energy in a highly-reversible electrical form important for many present and emerging applications.
Electrodes made from laser-scribed graphene can also be bent without any obvious change in their electrical properties, the researchers say. This holds promise not only for improved electrochemical capacitors but also for flexible gadgets, such as roll-up computer displays and keyboards as well as wearable electronics.
Such thin, highly flexible energy storage devices could lead to fabric electrochemical capacitors that store harvested body movement energy, potentially useful for making garments or military uniforms with embedded electronics, observes John Miller, president of JME, Inc., a Beachwood, OH, firm that offers engineering, performance testing and other services to electrochemical capacitor makers, in a commentary accompanying the Science report. Imagine car seats that heat up without a driver needing to flip a switch or electronic wallpaper that could change patterns or alter its brightness depending upon lighting conditions, Miller adds.
Graphic demonstrating graphene's ability to store electrical energy through the interaction with ions in an electrochemical capacitor courtesy of Science/AAAS