Researchers doped cobalt oxide with tin to create a more efficient electrode for use in supercapacitors. This microscopic image shows the new material on graphene film. (Courtesy Jia Zhu/Penn State)

A sustainable, powerful micro-supercapacitor may be on the horizon. Until now, these high-capacity, fast-charging energy storage devices have been limited by the composition of their electrodes. Now, researchers have developed a better material to improve connectivity while maintaining recyclability and low cost.

Although the supercapacitor is a very powerful, energy-dense device with a fast-charging rate, in contrast to the typical battery, researchers at Penn State (University Park, PA) wanted to be able to charge it even faster and achieve a really high retention cycle.

The researchers explored the connections in a micro-supercapacitor, which they use in their research on small, wearable sensors to monitor vital signs and more. Cobalt oxide, an abundant, inexpensive material that has a theoretically high capacity to quickly transfer energy charges, typically makes up the electrodes. However, the materials that mix with cobalt oxide to make an electrode can react poorly, resulting in a much lower energy capacity than theoretically possible.

The researchers ran simulations of materials from an atomic library to see if adding another material could amplify the desired characteristics of cobalt oxide as an electrode by providing extra electrons while minimizing, or entirely removing, the negative effects. They modeled various material species and levels to see how they would interact with cobalt oxide. Although they screened many possible materials, they found many that might work were too expensive or toxic, so they selected tin, which is widely available at a low cost, and is not harmful to the environment.

In their simulations, the researchers found that by partially substituting tin for some of the cobalt for and binding the material to a commercially available graphene film — a single-atom thick material that supports electronic materials without changing their properties — they could fabricate what they called a low-cost, easy-to-develop electrode.

Once the simulations were completed, a team in China conducted experiments that demonstrated that the simulation could be actualized.

Next, the researchers plan to use their own version of graphene film — a porous foam created by partially cutting and then breaking the material with lasers — to fabricate a flexible capacitor to allow for easy and fast conductivity.

“The supercapacitor is one key component, but we’re also interested in combining with other mechanisms to serve as both an energy harvester and a sensor,” said Professor Huanyu “Larry” Cheng. “Our goal is to put a lot of functions into a simple, self-powered device.”