Scientists at the Pacific Northwest National Laboratory (PNNL) of the US Department of Energy have created an aluminium-nickel (Al-Ni) molten salt battery named “freeze-thaw battery” under thermal cycling. It can disable the self-charge mechanism when the battery is turned off.
With a potential energy density of 260 W/hour per kilogramme, the battery will be able to preserve 92 per cent of its initial capacity over 12 weeks. It had an aluminium anode and a nickel cathode, both of which were submerged in a molten salt electrolyte.
To boost the battery's storage capacity, they added sulphur to the electrolyte. To prevent damage during the freeze-thaw cycle, a ceramic separator was implanted between the anode and the cathode.
“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,” stated researcher Minyuan Miller Li.
The battery is charged by heating it to roughly 180 degrees Celsius and allowing the ions to pass through the liquid electrolyte. When the device is brought back to room temperature, the electrolyte solidifies, trapping the ions that carry the stored energy. When energy is required, the ions restart flowing through the electrolyte, allowing the battery to be heated again. They used an aluminium anode and a nickel cathode, both of which were submerged in a molten salt electrolyte.
“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 PNNL battery uses simple fiberglass, possible because of the battery’s stable chemistry. This cuts costs and makes the battery sturdier when undergoing freeze-thaw cycles,” said the scientists.
“The battery’s energy is stored at a materials cost of about $23 per kilowatt-hour, measured before a recent jump in the cost of nickel. The team is exploring the use of iron, which is less expensive, in hopes of bringing the materials cost down to around $6 per kilowatt-hour, roughly 15 times less than the materials cost of today’s lithium-ion batteries,” added the scientists.
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