Cambridge, Mass.: A team of Harvard scientists and engineers announced the demonstration January 14 of a new type of battery that could fundamentally transform the way electricity is stored on the grid, making power from renewable energy sources such as wind and solar far more economical and reliable.
The team’s paper, published in Nature magazine January 9, reports a metal-free flow battery that relies on the electrochemistry of naturally abundant, inexpensive, small organic molecules called quinones, which are similar to molecules that store energy in plants and animals.
Flow batteries store energy in chemical fluids contained in external tanks—as with fuel cells—instead of within the battery container itself. The two main components—the electrochemical conversion hardware through which the fluids are flowed (which sets the peak power capacity), and the chemical storage tanks (which set the energy capacity)—may be independently sized. Thus the amount of energy that can be stored is limited only by the size of the tanks. The design permits larger amounts of energy to be stored at lower cost than with traditional batteries.
By contrast, in solid-electrode batteries, such as those commonly found in cars and mobile devices, the power conversion hardware and energy capacity are packaged together in one unit and cannot be decoupled. Consequently they can maintain peak discharge power for less than an hour before being drained, and are therefore ill suited to store intermittent renewables.
To store 50 hours of energy from a 1-megawatt power capacity wind turbine (50 megawatt-hours), for example, a possible solution would be to buy traditional batteries with 50 megawatt-hours of energy storage, but they’d come with 50 megawatts of power capacity. Paying for 50 megawatts of power capacity when only 1 megawatt is necessary makes little economic sense.
For this reason, a growing number of engineers have focused their attention on flow battery technology. Vanadium is used in the most commercially advanced flow battery technology now in development, but its cost sets a rather high floor on the cost per kilowatt-hour at any scale, the researchers explain. Other flow batteries contain precious metal electrocatalysts such as the platinum used in fuel cells. The new flow battery developed by the Harvard team already performs as well as vanadium flow batteries, with chemicals that are significantly less expensive, and with no precious metal electrocatalyst. Quinones are abundant in crude oil as well as in green plants. The molecule that the Harvard team used in its first quinone-based flow battery is almost identical to one found in rhubarb. The quinones are dissolved in water, which prevents them from catching fire.