Where to focus our energy policy?

Printed supercapacitor could feed power-hungry gadgets       

   ( April 10th 2009 by Colin Barras)     For similar stories, visit the Nanotechnology Topic Guide

A supercapacitor – a device that can unleash large amounts of charge very quickly – has been created using printing technology for the first time. The advance will pave the way for "printed" power supplies that could be useful as gadgets become thinner, lighter and even flexible.

Advances in electronics mean portable gadgets are shrinking in size but growing in their energy demands, and conventional batteries are struggling to cope.

Batteries are slow to recharge because they store energy chemically. By contrast, capacitors, which are common in electronics, are short-term stores of electrical energy that charge almost instantaneously but hold little energy.

In recent years capacitors able to store thousands of times as much energy as standard ones, called supercapacitors, have been developed. They are charged by applying a voltage to two electrodes suspended in a solution so that positive ions head to one electrode and negative ions to the other.

Now, a team led by George Grüner at the University of California, Los Angeles, has printed a supercapacitor for the first time, building on earlier theoretical work to provide quick bursts of power that today's electronics devices demand.

Team members sprayed carbon nanotubes onto a plastic film – two such films act as both the device's electrodes and charge collectors. Between the two films, the team sandwiched a gel electrolyte made by mixing a water-soluble synthetic polymer with phosphoric acid and water.

Experimental batteries

He thinks the real advance in the new work is in engineering – many researchers study the electrochemistry of potential flexible supercapacitor components, but no one has built a working flexible device before. "There's more than the electrochemistry to think about here – there are manufacturing and material selection issues to consider too," says Chen.

Both Grüner and Chen think portable devices will ultimately carry a battery and a supercapacitor to provide the high energy storage and fast energy discharges demanded by modern devices.

But Chen points out that experimental batteries show some promise towards filling both roles. They have the energy storage of normal batteries, but also possess a power density rivalling supercapacitors, meaning they can charge and release energy 100 times as fast as normal lithium ion batteries.

Journal reference: Nano Letters (DOI: 10.1021/nl8038579)