A hybrid device that is both solar cell and battery could address the problem of how to make Watts when the sun shines and use them later. Writing in the journal Nature Communications, Yiying Wu of The Ohio State University and colleagues explain how they have developed the first solar battery. The device integrates a redox-coupled dye-sensitized photoelectrode into a lithium-oxygen battery for photo-assisted charging, the team reports. [Wu et al.m Nature Commun, 2014 online]
The crucial feature allowing this novel solar cell to store energy is that it incorporates a mesh that allows air to enter the battery and a redox couple that couples this mesh photoelectrode with the air electrode. Within the device, light and oxygen enable different aspects of the chemical reactions that charge the battery with a special process allowing electron transfer between solar panel and the battery electrode. OSU will license the patented technology to industry and Wu suggests that it will help cut the costs of renewable energy by around 25 percent. The hybrid device also offers electrical efficiency improvements by cutting the inevitable losses - some 20 percent - seen in transferring energy from solar to storage in conventional systems.
"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," he explains. "We've integrated both functions into one device. Any time you can do that, you reduce cost."
The device builds on the earlier design of a potassium-oxygen battery by Wu and doctoral student Xiaodi Ren. "Basically, it's a breathing battery," Wu said. "It breathes in air when it discharges, and breathes out when it charges." The new hybrid device uses a permeable mesh solar panel - a dye-sensitized solar cell - made from flexible titanium gauze and titanium dioxide supporting a red dye that allows the battery to absorb sunlight and breathe, something that would not be possible with standard solid semiconductor solar panel materials. Moreover, the design requires only three, rather than the normal four electrodes to connect solar panel to battery. The mesh acts as the first electrode, with a thin sheet of porous carbon bellow and a layer of lithium as the third plate. Electrolyte is sandwiched between these layers and contains an iodide additive which "shuttles" electrons 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 team's next step is to achieve full photocharging and to improve solar battery's lifetime to be comparable to commercial rechargeable batteries, Wu told Materials Today.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".