A year of work by a materials science and engineering team has recently culminated in the development of a transparent lithium-ion battery, according to a paper recently published in the Proceedings of the National Academy of Sciences.

The finished product is not much more expensive than the widely available traditional lithium-ion battery, as the materials used to manufacture it are not expensive. The transparent battery is also rechargeable–similar to a normal lithium-ion battery–because it uses the same chemistry.

The battery is comprised of electrodes arranged in a mesh-like grid, with each line in the grid approximately 35 microns wide. This framework seems transparent to the naked human eye, because if something is smaller than 50 microns, it appears transparent.

Yuan Yang, a graduate student in materials science and engineering, did most of the experimental work involved with inventing the battery and contributed to the initial design of the concept.

“It is like a miniaturized screen window; when the line is thin enough, people’s eyes cannot distinguish it from the background, so it is transparent,” Yang said.

The electrodes themselves are made up of metal oxides, and the substrate is a transparent polymer called polydimethylsiloxane, more commonly referred to as “PDMS.”

“The transparency could vary by changing width of lines in the grid,” Yang said. “For example, it’s easy to vary the transparency from 40 percent to 90 percent.”

The amount of energy that the battery stores can also be altered. The transparent battery currently holds less energy than a traditional battery, but increasing its thickness changes that.

“The energy stored in a battery with 70 percent transparency is 30 percent of a traditional battery,” he said. “However, there are several ways to increase it–first, by increasing the thickness of the battery, which will not decrease the transparency at the same time. Second, with the development of new high-energy materials for batteries, the energy stored could be close to state-of-the-art batteries.”

Transparent batteries also serve a practical purpose: they allow examination of inner electronic workings for further research.

Yi Cui, associate professor of materials science and engineering, is the leading scientist on the team. Cui thinks that a transparent battery is the first step toward many other transparent objects, such as transparent cell phones, laptops and watches. He personally would like to see a transparent iPhone.

“It is exciting to lead my whole research group and come up innovative ideas in addressing different needs to society,” Cui said.