In the October 3, 2014 issue of the journal Nature Communications, the Ohio State researchers reported that they’ve succeeded in combining a battery and a solar cell into one hybrid device.
The key to the innovation is a mesh solar panel, which allows air to enter the battery, and a special process for transferring electrons between the solar panel and the battery electrode. Light and oxygen inside the device, allow different parts of the chemical reactions that charge the battery.
Professor of chemistry and biochemistry at Ohio State, Yiying Wu said that the university will license the solar battery to industry, which will help tame the costs of renewable energy.
“The state of the art is to use a solar panel to capture the light, and then use a cheap battery to store the energy,” Wu said. “We’ve integrated both functions into one device. Any time you can do that, you reduce cost.” Wu believes that the device will bring costs down by 25 percent.
The invention also solves a longtime problem in solar energy efficiency, by eliminating the loss of electricity that normally occurs when electrons have to travel between a solar cell and an external battery. Usually, only 80 percent of the electrons that emerge from a solar cell make it into a battery. With this new design, light is converted into electrons inside the battery, so nearly 100 percent of the electrons are saved.
The design of the battery takes some of its idea from a battery that Wu and doctoral student Xiaodi Ren previously developed. They invented a high-efficiency air-powered battery that discharges by a potassium and oxygen chemical reaction. The design won the $100,000 clean energy prize from the U.S. Department of Energy in 2014, and researchers formed a technology spin-off company called KAir Energy Systems, LLC to develop it.
“Basically, it’s a breathing battery,” Wu said. “It breathes in air when it discharges, and breathes out when it charges.”
For this new study, the researchers wanted to combine a solar panel with a battery similar to the KAir. The challenge they faced was that solar cells are normally made of solid semiconductor panels, which would block air from entering the battery.
This lead to doctoral student Mingzhe Yu designing a permeable mesh solar panel from titanium gauze, a flexible fabric upon which he grew vertical rods of titanium dioxide like blades of grass. Air passes freely through the gauze while the rods capture sunlight.
During charging, light hits the mesh solar panel and creates electrons. Inside the battery, electrons are involved in the chemical decomposition of lithium peroxide into lithium ions and oxygen. The oxygen is released into the air, and the lithium ions are stored in the battery as lithium metal after capturing the electrons.
When the battery discharges, it chemically consumes oxygen from the air to re-form the lithium peroxide. An iodide additive in the electrolyte acts as a “shuttle” that carries electrons, and transports them between the battery electrode and the mesh solar panel. The use of the additive represents a distinct approach on improving the battery performance and efficiency, the team said.