In a recent paper published in Cell Reports Physical Science, they demonstrated how freezing and thawing a molten salt solution creates a rechargeable battery that can store energy cheaply and efficiently for weeks or months at a time.
Most conventional batteries store energy as chemical reactions waiting to happen. When the battery is connected to an external circuit, electrons travel from one side of the battery to the other through that circuit, generating electricity. To compensate for the change, charged particles called ions move through the fluid, paste or solid material that separates the two sides of the battery. But even when the battery is not in use, the ions gradually diffuse across this material, which is called the electrolyte. As that happens over weeks or months, the battery loses energy. Some rechargeable batteries can lose almost a third of their stored charge in a single month.
“In our battery, we really tried to stop this condition of self-discharge,” says PNNL researcher Guosheng Li, who led the project. The electrolyte is made of a salt solution that is solid at ambient temperatures but becomes liquid when heated to 180 degrees Celsius—about the temperature at which cookies are baked. When the electrolyte is solid, the ions are locked in place, preventing self-discharge. Only when the electrolyte liquifies can the ions flow through the battery, allowing it to charge or discharge.
Right now the experimental technology is aimed at utility-scale and industrial uses. Sprenkle envisions something like tractor-trailer truck containers with massive batteries inside, parked next to wind farms or solar arrays. The batteries would be charged on-site, allowed to cool and driven to facilities called substations, where the energy could be distributed through power lines as needed.
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