Stanford scientists have developed a water-based battery that could provide a cheap way to store wind or solar energy, which can be fed back into the electric grid and redistributed when the demand is high.

The prototype manganese-hydrogen battery, described in the journal Nature Energy, stands just three inches tall and generates a mere 20 milliwatt hours of electricity, which is on par with the energy levels of LED flashlights one might hang on a key ring.

The researchers are confident they can take this table-top technology up to an industrial-grade system that could charge and recharge up to 10,000 times, creating a grid-scale battery with a useful lifespan well in excess of a decade.

Manganese-hydrogen battery technology could be one of the missing pieces in the energy puzzle – a way to store unpredictable wind or solar energy so as to lessen the need to burn reliable but carbon-emitting fossil fuels when the renewable sources are not available, said Yi Cui, senior author on the paper and a professor at Stanford University.

“What we have done is thrown a special salt into water, dropped in an electrode, and created a reversible chemical reaction that stores electrons in the form of hydrogen gas,” Cui said. The researchers coaxed a reversible electron-exchange between water and manganese sulphate, a cheap, abundant industrial salt used to make dry cell batteries, fertilisers, paper and other products.

To mimic how a wind or solar source might feed power into the battery, the researchers attached a power source to the prototype. The electrons flowing in reacted with the manganese sulphate dissolved in the water to leave particles of manganese dioxide clinging to the electrodes. Excess electrons bubbled off as hydrogen gas thus storing that energy for future use. Engineers know how to recreate electricity from the energy stored in hydrogen gas so the important next step was to prove was that the water-based battery can be recharged.

The researchers did this by re-attaching their power source to the depleted prototype, this time with the goal of inducing the manganese dioxide particles clinging to the electrode to combine with water, replenishing the manganese sulphate salt. Once this salt was restored, incoming electrons became surplus, and excess power could bubble off as hydrogen gas, in a process that can be repeated in cycles.

According to DOE estimates, about 70 percent of U.S. electricity is generated by coal or natural gas plants, which account for 40 percent of carbon dioxide emissions. Shifting to wind and solar generation is one way to reduce those emissions.

Given the water-based battery’s expected lifespan, it would cost a penny to store enough electricity to power a 100-watt lightbulb for twelve hours,” said Cui. “The breakthrough we report in Nature Energy has the potential to meet DOE’s grid-scale criteria,” Chen said.