Liquid metal batteries can hold sizable amounts of energy, and can make power production and use more consistent.
These innovative batteries made their debut 10 years ago, invented by MIT professor Donald Sadoway and his students. Now Sadoway's team has figured out that a different set of chemicals could make the whole process more affordable and practical - and could potentially enable the use of local resources.
The scientific team showed in a recent paper that the plentiful and cheap element calcium can be the foundation for both the battery's negative electrode layer and the middle layer of three in the battery, which is molten salt.
To learn that something as simple as an antacid ingredient would fill out these batteries was a very unexpected finding, said Sadoway. Some of calcium's properties seem unlikely for this use - for instance, calcium dissolves easily in salt. However, it works in this situation, even though the layers must be kept separate and not mix at boundaries.
Knowing those limitations, making calcium work in a liquid battery was part of the puzzle that the team had to solve. "For me, I'm happiest with whatever is most difficult," said co-author Takanari Ouchi.
Calcium also has a high melting point. The team dealt with this obstacle by alloying the calcium (combining it with another cheap metal, magnesium). The latter has a lower melting point. This made a mixture that had a lower operating temperature but was also able to handle high volts.
The new battery solution also used an innovation in forming the salt in its middle layer. The salt is also known as the electrolyte and can charge the ions that move across the battery as it is used. In this case, the salt mix was lithium chloride and calcium chloride. When combined, they solved the problem of dissolving too easily.
There's another advantage to using the cheap materials magnesium and calcium: The two are often found together in their natural state and might be even simpler and less expensive to source than thought. "There's an irony here. If you're trying to find high-purity ore bodies, magnesium and calcium are often found together," Sadoway said. Because the battery will need a combination of the two, it might be possible to save on costs by sourcing less-expensive grades of the two metals that are less pure and already hold parts of the other metal.
"The lesson here is to explore different chemistries and be ready for changing market conditions," Sadoway said. The new development "is not a battery; it's a whole battery field. As time passes, people can explore more parts of the periodic table" to make even better formulae.
The findings were published in the journal Nature Communications.
