Researchers at Harvard have developed an inexpensive, high capacity, organic battery that uses carbon-based materials as electrolytes rather than metals. The researchers say the technology stands to be a game-changer in renewable energy storage by solving the intermittent generation problems faced by renewable sources, such as wind and solar. The battery offers large volume electricity storage not possible with solid-state batteries and at a fraction of the cost of existing flow battery technology.

Energy in flow batteries is stored in fluids held in external tanks, meaning storage capacity is only limited by the size of the tanks. As a result, larger amounts of energy can be stored than in traditional solid-electrode batteries. However, existing flow battery technology uses expensive metals, such as vanadium or platinum, as electrolytes, resulting in a high cost per kilowatt-hour of storage.

“The whole world of electricity storage has been using metal ions in various charge states but there is a limited number that you can put into solution and use to store energy, and none of them can economically store massive amounts of renewable energy,” says Professor Roy Gordon, the Thomas D. Cabot Professor of Chemistry at Harvard.

The Harvard approach utilizes the electrochemistry of quinones, organic molecules that are similar to molecules that store energy in plants and animals and are plentiful in crude oil and green plants. Using these naturally abundant and inexpensive organic molecules, the researchers have developed a metal-free flow battery that already performs as well as vanadium flow batteries, while using significantly less expensive chemicals and no precious metals.

“With organic molecules, we introduce a vast new set of possibilities," says Professor Gordon. "Some of them will be terrible and some will be really good. With these quinones we have the first ones that look really good.”

Using high-throughput molecular screening, over 10,000 quinone molecules were examined and one almost identical to that found in rhubarb was selected. The quinones are dissolved in water to prevent them from catching fire.

Large storage tanks would be needed to capture the energy produced by commercial solar or wind facilities. It has been proposed these could be either placed on-site or integrated into the grid. At a household level, smaller batteries could be used, making the technology a useful backup for the 20 percent of the global population that are off-grid.

"Imagine a device the size of a home heating oil tank sitting in your basement," says study co-lead author Michael Marshak. "It would store a day’s worth of sunshine from the solar panels on the roof of your house, potentially providing enough to power your household from late afternoon, through the night, into the next morning, without burning any fossil fuels,"

The technology now faces a grueling testing process to assess the degradation rate over thousands of cycles, with early tests indicating no signs of degradation. A Connecticut-based commercial collaborator, Sustainable Innovations, hopes to have a portable demonstration model ready in around three years and will bring the product to market when ready.

The team's research was published in the journal Nature. Under the OPEN 2012 program, the Harvard team received funding from the US Department of Energy’s Advanced Research Projects Agency–Energy (ARPA-E).

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