Aug 3 2015
Doctoral students Billy McCulloch (left) and Mingzhe Yu (right) of The Ohio State University with a prototype of the new aqueous solar flow battery. (Credit: Kevin Fitzsimons, courtesy of The Ohio State University)
The Ohio State University researchers have now achieved a milestone to success, following the debut of the world's first solar air battery the previous year.
Their patent-pending design, which integrates both solar cell and battery into a single device is capable of achieving 20% energy savings when compared to conventional lithium-iodine batteries.
Yiying Wu, professor of chemistry and biochemistry at Ohio State explained that 20% is due to sunlight captured using a unique solar panel on top of the battery. Unlike the previous design made up of mesh, this new solar panel is in the form of a solid sheet.
The use of a water-based electrolyte within the battery is another major difference. With the circulation of water inside the cell, the new design comes under the category of emerging type of batteries known as aqueous flow batteries.
"The truly important innovation here is that we've successfully demonstrated aqueous flow inside our solar battery," Wu said.
This is the first aqueous flow battery, as such, with solar capability. Or it can be called the first "aqueous solar flow battery," as Wu and his team stated.
"It's also totally compatible with current battery technology, very easy to integrate with existing technology, environmentally friendly and easy to maintain," he added.
In theory, it could be possible for the researchers to offer inexpensive power grid-level energy storage sometime and hence, a number of researchers worldwide are focusing on the development of aqueous flow batteries.
The solar flow battery could hence, fill a gap between the existing energy grid and renewable energy sources.
"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.
In the earlier experiment, Yu used titanium mesh to design the solar panel so as to allow the air to pass via the battery. However, the new aqueous flow battery avoids the need for air during operation, and hence the solar sheet is a solid sheet.
The researchers used a red dye to tweak the wavelength of light captured by the solar panel and convert it into electrons. The voltage stored in the lithium-anode portion of the solar battery is supplied by these electrons.
The electrolyte serves as a means to carry electrons from the solar cell into the battery. Typically, a liquid electrolyte is a part salt, part solvent. The researchers previously used the salt lithium perchlorate combined with the organic solvent dimethyl sulfoxide. In the current research, they used lithium iodide as the salt, and water as the solvent. (Water is an eco-friendly inorganic solvent. Lithium iodide is inexpensive and has a high-energy storage capacity.)
During the tests, the performance of the solar flow battery was compared to that of a typical lithium-iodine battery. The batteries were charged and discharged 25 times. Both batteries discharged around 3.3V for each time.
The difference suggested that the same output could be produced with less charging using the solar flow battery. The typical battery needs to be charged to 3.6V to discharge 3.3V. The solar flow battery however, was charged to only 2.9V due to the difference in the solar panel, resulting in nearly 20% of energy savings.
The project is under way, and the solar flow design will certainly evolve once again as the researchers make continuous efforts to make batteries more efficient.
According to doctoral student and study co-author Billy McCulloch, the research could lead to many possible directions.
"We hope to motivate the research community to further develop this technology into a practical renewable energy solution," he added.
The main goal of the research group is to improve the contribution of the solar cell to the battery over its current 20%, may be even to 100%.
"That's our next step," Wu said, "to really achieve a fully solar-chargeable battery."