US scientists have developed a battery that can retain 92% of its initial capacity over periods of 12 weeks, with a theoretical energy density of 260 W/hour per kg. It was built with an aluminum anode and a nickel cathode, immersed in molten-salt electrolyte.

Scientists at the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) have developed an aluminum-nickel (Al-Ni) molten salt battery that, under thermal cycling, exhibits high retention of cell capacity over periods of weeks.

The scientists described the small prototype as a “freeze-thaw battery” that cuts off the self-charge function when a battery is idling. “It’s a lot like growing food in your garden in the spring, putting the extra in a container in your freezer, and then thawing it out for dinner in the winter,” explained researcher Minyuan Miller Li.

The battery is charged by heating it to around 180 C, with its ions flowing through the liquid electrolyte. The device is then restored to room temperature and the electrolyte becomes solid, thus trapping the ions that transport the stored energy.

“The freeze-thaw phenomenon is possible because the battery’s electrolyte is molten salt – a molecular cousin of ordinary table salt. The material is liquid at higher temperatures but solid at room temperature,” the scientists said.

They noted that the battery can be heated again, as the ions restart flowing through the electrolyte when energy is needed. They built it with an aluminum anode and a nickel cathode, immersed in a sea of molten-salt electrolyte.

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