Researchers are generating modified alkaline batteries that can be recharged thousands of times and perhaps even indefinitely, offering affordable energy storage for areas prone to severe storms, as well as to off-grid regions, such as the Navajo Nation.
"That's always been the first objective: to provide capacity assurance when the sun doesn't shine, when the wind doesn't blow, and do it really inexpensively," co-inventor Sanjoy Banerjee, a distinguished professor at The City College of New York and the director of its Energy Institute, told The Academic Times.
Banerjee and his team have filed a patent application for the most recent enhancement to their mixed-material battery, and it was published by the World Intellectual Property Organization on May 6.
"What we tried to do was to make [alkaline batteries] 'upcyclable' so that we could get similar costs and make them rechargeable — like lead-acid or lithium-ion batteries." Banerjee said.
He noted that the first versions of these batteries are already being deployed in the Navajo Nation, within which houses are not connected to the power grid and rely on intermittent power from personal wind turbines or solar panels. The batteries have also gained interest from members of the San Diego Supercomputer Center, who are worried about power failures, particularly given the recent wildfires in California.
Of course, power outages do not occur only in areas prone to storms. Banerjee noted that the power grid can often fail because renewable energy, while sustainable and clean, tends to run unstably.
"During the day, people may not need the power as much as in the evening, when they come home and they turn on the air conditioners," he explained. "Yet there is no sun at that time to provide the power, so that mismatch causes a fair amount of grid instability, which can also lead to power outages."
If an affordable and rechargeable battery can be implemented, it would store power for the nighttime, when outages are imminent.
Reflected in the recently published patent application, alterations to the original design ensure that dissolved zinc from the battery's anode does not cross over to the manganese-based cathode. That prevents the chemicals from forming inactive products, which can reduce conductivity during recharge.
Banerjee and his team have filed two other patents related to the invention, both of which have already been awarded. A recent one describes the researchers' upcoming plans to increase the voltage of the storage device, which ultimately aims to make the item lighter.
"That's been the next frontier," Banerjee explained. "The advantage you would have is a very nonflammable battery for electric vehicles — and also inexpensive."
The other patent draws up the basic concept of the team's zinc-manganese dioxide design.
"We chose zinc and manganese dioxide because these are extremely inexpensive materials; they're widely available," Banerjee said. "They're actually what you use in your AA and AAA batteries."
Typically, alkaline batteries made with these chemicals cannot be charged for many cycles without losing their effectivity and quickly dying. That's because the manganese dioxide within the battery — in the form of a fragile crystal lattice — loses its structure during a process called proton insertion.
"You progressively degrade it — perhaps not in one shot — but in subsequent cyclings. You gradually pile up these inactive components," Banerjee said. "It's a dead battery after that."
To get around that issue — but still retain the low-cost materials — the team added small percentages of two new elements to the traditional alkaline battery's composition: bismuth and copper, the latter of which increases the stability of the reaction.
"It's three times or four times as expensive as the manganese dioxide ... but it's not enough to make it uneconomic — it's still the most inexpensive battery you can make," Banerjee said. "Let's say this costs $20 a kilowatt-hour. With the bismuth birnessite and everything, we can make this for about $40 a kilowatt-hour — but it can be charged hundreds of thousands of times."
Rather than attempt to prevent the manganese-dioxide structure from degrading, the team allows its natural deterioration to occur. The addition of copper and bismuth, which alternate with the manganese dioxide in a plane-like pattern called a lamellar structure, allows the degraded chemical to cycle for more charges.
"You kill it completely, and then you bring it back," Banerjee said. "With the bismuth and the copper, you can bring it back, and then it will cycle forever."
The patent application, "Mitigating the zincate effect in energy dense manganese dioxide electrodes," was filed Oct. 30, 2020. It was published May 6 by the World Intellectual Property Organization with the application number WO/2021/087327. The earliest priority date was Oct. 31, 2019, and the inventors listed are Gautam G. Yadav, Xia Wei, Michael Nyce and Sanjoy Banerjee. The applicant listed is Research Foundation of The City University of New York.
Parola Analytics provided technical research for this story.