Researchers develop a solar battery 20% more efficient that today's Lithium-iodine batteries.
Imagine to be able to recharge battery by just lying them into the sun.
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Researchers at The Ohio State University have reached a milestone in achieving this goal.
Combining a solar cell and a battery into a single device, the researchers achieve a 20% energy savings over traditional lithium-iodine batteries.
"The 20% comes from sunlight, which is captured by a unique solar panel on top of the battery," explained Yiying Wu, professor of chemistry and biochemistry at Ohio State.
The solar panel is now a solid sheet, rather than a mesh as in the previous design the researchers unveiled last year in the first solar air battery.. Another key difference comes from the use of a water-based electrolyte inside the battery.
The new design belongs to an emerging class of batteries called aqueous flow batteries.
"The truly important innovation here is that we've successfully demonstrated aqueous flow inside our solar battery," Wu said.
As such, it is the first aqueous flow battery with solar capability. Or, as Wu and his team have dubbed it, the first "aqueous solar flow battery."
"It's also totally compatible with current battery technology, very easy to integrate with existing technology, environmentally friendly and easy to maintain," he added.
Aqueous flow batteries are a new research focus as they could theoretically provide affordable power grid-level energy storage someday.
"This solar flow battery design can potentially be applied for grid-scale solar energy conversion and storage, as well as producing 'electrolyte fuels' that might be used to power future electric vehicles," said Mingzhe Yu, lead author of the paper and a doctoral student at Ohio State.
Previously, Yu designed the solar panel out of titanium mesh, so that air could pass through to the battery. But the new aqueous flow battery doesn't need air to function, so the solar panel is now a solid sheet.
The solar panel is called a dye-sensitized solar cell, because the researchers use a red dye to tune the wavelength of light it captures and converts to electrons.
Those electrons then supplement the voltage stored in the lithium-anode portion of the solar battery.
Something has to carry electrons from the solar cell into the battery, however, and that's where the electrolyte comes in.
A liquid electrolyte is typically part salt, part solvent; previously, the researchers used the salt lithium perchlorate mixed with the organic solvent dimethyl sulfoxide.
Now they are using lithium iodide as the salt, and water as the solvent. (Water is an inorganic solvent, and an eco-friendly one. And lithium iodide offers a high-energy storage capacity with low cost.)
In tests, the researchers compared the solar flow battery's performance to that of a typical lithium-iodine battery.
They charged and discharged the batteries 25 times. Each time, both batteries discharged around 3.3 volts.
The difference was that the solar flow battery could produce the same output with less charging.
The typical battery had to be charged to 3.6 volts to discharge 3.3 volts. The solar flow battery was charged to only 2.9 volts, because the solar panel made up the difference. That's an energy savings of nearly 20%.
The team's ultimate goal is to boost the solar cell's contribution to the battery past its current 20% and reach eventually 100%. This would allow consumers to just expose batteries to sunlight to recharge them.
"That's our next step," Wu said, "to really achieve a fully solar-chargeable battery."
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The paper titled "Aqueous Lithium–Iodine Solar Flow Battery for the Simultaneous Conversion and Storage of Solar Energy" was published in the Journal of the American Chemical Society.