MIT researchers have revived a 50-year-old battery chemistry by outfitting it with new technology for separating materials in its electrode, making the new design a leading option to provide grid-scale alternative-energy storage in the future, they said.
A team led by Donald Sadoway, an MIT professor of materials chemistry, used a battery made of nickel and liquid-sodium electrode materials in its research, adding a specially coated metal mesh membrane to separate the battery’s molten materials. The metal material is much stronger and more flexible than the ceramic previously used for the membrane, making the battery able to withstand the rigors of use required by industrial-scale storage systems, he said.
“I consider this a breakthrough,” Sadoway said. This is because for the first time in five decades, this type of battery—the advantages of which include inexpensive, abundant raw materials, safe operational characteristics, and the capability to experience multiple charge-discharge cycles without degradation--could finally become practical, he said.
A photo illustration shows how a type of battery first invented nearly five decades ago could be a serious contender to provide grid-scale alternative-energy storage, thanks to new technology designed for it by researchers at MIT. (Source: Felice Frankel, MIT)
Scientists first described this sodium-nickel battery as a concept in 1968 but the idea never caught on because of a major drawback to the design—it required the use of a thin membrane to separate its molten components.
Moreover, the only known material with the needed properties for that membrane at the time was a brittle and fragile ceramic, which rendered the batteries too easily damaged in real-world operating conditions, researchers said. While this type of battery was used in some specialized industrial applications, to date it not widely used.
That could all change now with the MIT’s team’s invention, which actually came about as a surprise as researchers explored various options for compounds in their quest to design a molten-metal-based battery, they said.
When they opened the cell after one of their tests using lead compounds, researchers found droplets of molten lead acting not just as a separating membrane, but as an electrode, Sadoway said.
“That really opened our eyes to a completely different technology,” he said. The membrane had performed its role—which is to allow certain molecules to pass through while blocking others—in an entirely different way, using its electrical properties rather than the typical mechanical sorting based on the sizes of pores in the material.
The team experimented with various compounds and found that an ordinary steel mesh coated with a solution of titanium nitride could perform all the functions of the previously used ceramic membranes, but without the brittleness and fragility, Sadoway said.
Researchers published a paper on their work in the journal Nature.
Their invention now paves the way for an entirely new family of inexpensive and durable materials for building large-scale, rechargeable batteries like those needed to store intermittent, alternative energies—such as solar and wind--for use by the electricity grid.
However, there are some uses for the batteries that would not be practical, Sadoway warned, such as to replace lithium-ion batteries in automobiles or mobile devices. Rather, their sweet spot for utilization is in large, fixed installations where cost is paramount, but size and weight are not, such as utility-scale load leveling, he said.
The team’s use of a new type of membrane also can be transferred to a wide variety of other battery chemistries that use molten-liquid electrodes, Sadoway added.
“The fact that you can build a sodium-sulfur type of battery, or a sodium/nickel-chloride type of battery, without resorting to the use of fragile, brittle ceramic--that changes everything,” he said.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years.