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Ten years ago, Donald Sadoudow, a professor of materials chemistry at the Massachusetts Institute of Technology, and his students invented large-capacity liquid metal batteries. Now his team has discovered a new chemical component that can make this technology cheaper and more practical - calcium, which opens the way for the large-scale application of liquid metal batteries.
Their latest research published in the journal Nature Communications shows that calcium, a rich and inexpensive chemical element, can be an important raw material for three-layer liquid metal batteries.
Sadovi said that this discovery is unexpected, because the calcium properties make it almost impossible to become a raw material for liquid metal batteries. On the one hand, calcium is easily dissolved in salt solutions. However, one of the main features of liquid metal batteries is that three key components of it form mutually independent layers; on the other hand, calcium has a very high melting point. Raw materials, liquid metal batteries have to work at high temperatures of 900 degrees Celsius.
However, this seemingly minimal material has aroused the interest of researchers. Because the cheap calcium can greatly reduce the cost of the liquid metal battery, and its inherent high voltage performance makes it an excellent "candidate" for the negative electrode layer of liquid metal batteries.
To solve the melting point of calcium, the researchers alloyed calcium with cheap magnesium, which has a melting point much lower than that of calcium. The combination of the two lowers the original melting point by 300 degrees Celsius while still maintaining the high pressure performance of calcium.
Another innovation is the design of electrolytes in the middle layer of liquid metal cells. When the battery is in use, ions will move in the electrolyte. With their movement, the current will pass through the wires connecting the two poles of the liquid metal battery.
The newly designed electrolyte contains a mixture of lithium chloride and calcium chloride, and the calcium magnesium alloy as the negative electrode layer is not easily dissolved in the electrolyte. This design also brought new surprises. Normally, the moving ions are acting alone in a powered battery. For example, only lithium ions in a lithium-ion battery will move, and only sodium ions will move in a sodium-sulfur battery. However, the researchers found that in the latest design, a variety of ions will move in the electrolyte, increasing the overall energy output of the battery.
Sadovi said that this accidental discovery will open up a new path for battery design. He said: "With the passage of time, we can explore more elements of the chemical periodic table to find a better battery recipe." (Reporter Liu Yuanyuan)
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