In October 3, 2014 researchers reported in the the journal Nature Communications, that they’ve succeeded in combining a battery and a solar cell into a hybrid device.
Giving birth to what became the first Solar Battery. This revolutionary artifact was created in The Ohio State University by Yiying Wu, professor of chemistry. “Basically, it's a breathing battery” Wu said. "It breathes in air when it discharges, and breathes out when it charges".
Wu’s team believes that their device will reduce the costs of the solar panel and its battery by 25 percent. Based on early tests, Wu and his team think that the solar battery's lifetime will be comparable to rechargeable batteries already on the market. The invention also solves a longstanding setback in solar energy efficiency, by eliminating the loss of electricity that in general occurs when electrons have to travel between a solar cell and an external battery. On average, only 80 percent of electrons rising from a solar cell make it into a battery. Yet with this new design nearly a 100 percent of the electrons are saved.
The design of the solar battery takes some cues from a battery previously developed by Wu and doctoral student Xiaodi Ren. The previous invention consisted of a high-efficiency airpowered battery that discharges by chemically reacting potassium with oxygen.
HOW DOES IT WORK
During charging, light hits the mesh¹ solar panel and generates 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 and the process begins again.
An iodide additive in the electrolyte² acts as a "shuttle" that carries electrons, and moved them between the battery electrode³ and the mesh solar panel. The team specified that the use of the additive represents a distinct approach on improving the battery performance and efficiency.
During the tests, the team charged and discharged the battery repeatedly, while doctoral student Lu Ma used X-ray Photoelectron spectroscopy to analyze how well the electrode materials survived, this is an indication of battery life.
CHALLENGES FACED
The first challenge was that solar cells are normally made of solid semiconductor panels, which would block air from entering the battery. As a solution Doctoral student Mingzhe Yu designed a permeable mesh solar panel from titanium gauze, a flexible fabric upon which he grew vertical rods of titanium dioxide. Doing that air could passes freely through the gauze while the rods capture sunlight.
Secondly, they tried to use a ruthenium compound as the red dye, but since the dye was consumed in the light capture, the battery ran out of dye after eight hours of charging and discharging, which was a way too short a lifetime. So they turned to a dark red semiconductor that wouldn't be consumed: hematite, or iron oxide, best known as rust.
Currently The U.S. Department of Energy funds this project, which will continue as the researchers explore ways to enhance the solar battery's performance with new materials.
The story is provided by Ohio State University. The original article was written by Pam Frost Gorder. Note: Materials may be edited for content and length.
¹ Mesh = an interlaced structure.
² Electrolyte = liquid or gel that contain ions and can be decomposed by electrolysis.
³ Electrode = a conductor through which electricity enters or leaves an object, substance, or region.
Journal Reference:
Mingzhe Yu, Xiaodi Ren, Lu Ma, Yiying Wu. Integrating a redox-coupled dye-sensitized photoelectrode into a lithium–oxygen battery for photoassisted charging. Nature Communications,
2014; 5: 5111 DOI: 10.1038/ncomms6111
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