World's first solar battery promises cheaper energy supply

Electron microscope images show nanometer-sized rods of titanium dioxide (larger image) which cover the surface of a piece of titanium gauze (inset). The holes in the gauze are approximately 200 micrometers across, allowing air to enter the battery while the rods gather light.

The world's first solar battery – a combination of a solar cell and battery – which recharges itself using air and light could dramatically reduce the costs of renewable energy.

The key to the hybrid device 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.

Inside the device, light and oxygen enable different parts of the chemical reactions that charge the battery.

That leads to much greater efficiency by eliminating the loss of electricity that normally occurs when electrons have to travel between a solar cell and an external battery. Typically, only 80% of electrons emerging from a solar cell make it there.

With this new design, light is converted to electrons inside the battery, so nearly 100% of the electrons are saved.

The Ohio State University, where the device was invented, will license to to industry.

"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," says Yiying Wu, professor of chemistry and biochemistry. "We've integrated both functions into one device. Any time you can do that, you reduce cost."

The device consists of a permeable mesh solar panel made from titanium gauze, a flexible fabric upon which is "grown" vertical rods of titanium dioxide like blades of grass. Air passes freely through the gauze while the rods capture sunlight.

The mesh solar panel forms the first electrode, a thin sheet of porous carbon underneath that is a second electrode and a lithium plate, the third electrode. Between the electrodes, they sandwiched layers of electrolyte to carry electrons back and forth.

Here's how the solar battery works: 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.

The project was funded by the US Department of Energy. The study is reported in Nature Communications.

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