Wei Chen Jinwei Xu

Water-based Batteries Could Store Solar and Wind Energy

This low-cost battery is safe and can store energy for long periods of time.

Stanford researchers have developed a water-based battery that could provide a cheap way to store wind or solar energy generated when the sun is shining and wind is blowing, letting it be fed back into the electric grid and be redistributed when demand is high.

The prototype manganese-hydrogen battery is only three inches tall and generates a mere 20 milliwatt hours of electricity. 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 useful lifespan well in excess of a decade. The key innovation in the design of the battery is the development of a reversible electron-exchange between water and manganese sulfate salt, a cheap, abundant industrial salt used to make dry cell batteries, fertilizers, paper, and other products.

Electrons flowing in react with the manganese sulfate dissolved in the water to leave particles of manganese dioxide clinging to the electrodes. Excess electrons bubble off as hydrogen gas, thus storing that energy for future use. Engineers can then use the hydrogen to generate electricity. To recharge the battery, the researchers reattached a 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.

Wei Chen, a researcher at Stanford, holds a prototype battery that uses water and manganese-hydrogen in a water-based chemical reaction developed in the lab. (Image credit: Jinwei Xu)

The team estimates that, given the water-based battery’s expected lifespan, it would cost a penny to store enough electricity to power a 100-W lightbulb for 12 hours.

The Department of Energy (DOE) has recommended that 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.

The prototype still needs development work to prove itself. For one thing, it uses platinum as a catalyst to spur the crucial chemical reactions at the electrode during recharging to make the process efficient. The cost of that component would be prohibitive for large-scale deployment. The team is already working on cheaper ways to coax the manganese sulfate and water to perform the reversible electron exchange. They have identified catalysts that could bring costs below the $100-per-kilowatt-hour DOE target.

The researchers reported doing 10,000 recharges of the prototypes, which is twice the DOE requirements, but 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. The team leader is trying to patent the process through the Stanford Office of Technology Licensing and plans to form a company to commercialize the system.

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