Researchers at Stanford University have developed a water-based battery that has the potential to provide a cheap way to store wind or solar energy, the university has announced.
According to Stanford, the manganese-hydrogen battery could fill a missing piece in the nation’s energy puzzle by storing wind and solar energy for when it is needed – in turn, lessening the need to burn carbon-emitting fossil fuels.
The prototype battery, reported on Monday 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 that hang on a key ring, explains Stanford. Despite the prototype’s diminutive output, the researchers are confident they can scale up the technology to an industrial-grade system that could charge and recharge up to 10,000 times – creating a grid-scale battery with a lifespan well in excess of a decade, says Stanford.
“What we’ve 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,” says Yi Cui, a professor of materials science at Stanford and senior author on the paper.
The team that came up with the concept and built the prototype was led by Wei Chen, a postdoctoral scholar in Cui’s lab. In essence, the researchers coaxed a reversible electron-exchange between water and manganese sulfate – a cheap, abundant industrial salt used to make dry cell batteries, fertilizers, paper and other products – the university explains.
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 sulfate 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. According to Stanford, engineers know how to recreate electricity from the energy stored in hydrogen gas, so the important next step was to prove 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 sulfate 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 again and again and again.
Cui estimated that, given the water-based battery’s expected lifespan, it would cost a penny to store enough electricity to power a 100-watt lightbulb for 12 hours.
“We believe this prototype technology will be able to meet Department of Energy goals for utility-scale electrical storage practicality,” Cui says.
The Department of Energy (DOE) has recommended batteries for grid-scale storage should store and then discharge at least 20 kilowatts of power over a period of an hour, be capable of at least 5,000 recharges, and have a useful lifespan of 10 years or more. To make it practical, such a battery system should cost $2,000 or less, or $100 per kilowatt-hour, says Stanford.
Cui says there are several types of rechargeable battery technologies on the market, but it isn’t clear which approaches will meet DOE requirements and prove their practicality to the utilities, regulators and other stakeholders who maintain the nation’s electrical grid.
For instance, Cui says rechargeable lithium-ion batteries, which store the small amounts of energy needed to run phones and laptops, are based on rare materials and are thus too pricey to store power for a neighborhood or city. Cui says grid-scale storage requires a low-cost, high-capacity, rechargeable battery, and the manganese-hydrogen process is promising, Stanford says.
“Other rechargeable battery technologies are easily more than five times of that cost over the life time,” Cui adds.
However, according to Stanford, the prototype needs development work to prove itself. For one thing, it uses platinum as a catalyst to spur the crucial chemical reactions at the electrode that make the recharge process efficient, and the cost of that component would be prohibitive for large-scale deployment. But Chen says the team is already working on cheaper ways to coax the manganese sulfate and water to perform the reversible electron exchange.
“We have identified catalysts that could bring us below the $100 per kilowatt-hour DOE target,” he says.
The researchers reported doing 10,000 recharges of the prototypes – which is twice the requirements of the DOE – but said it will be necessary to test the manganese-hydrogen battery under actual electric grid storage conditions in order to truly assess its lifetime performance and cost.
Cui says he has sought to patent the process through the Stanford Office of Technology Licensing and plans to form a company to commercialize the system.
Additional co-authors of the paper include Guodong Li, a visiting scholar in materials science and engineering who is now with the Chinese Academy of Sciences; postdoctoral scholars Hongxia Wang, Jiayu Wan, Lei Liao, Guangxu Chen and Jiangyan Wang; visiting scholar Hao Zhang; and graduate students Zheng Liang, Yuzhang Li and Allen Pei. The work was funded by the DOE.
