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Pacific Northwest Lab Scientists Develop Prototype ‘Seasonal’ Battery

Scientists at Pacific Northwest National Laboratory say they have developed a “freeze-thaw” battery that could potentially provide long-term “seasonal” energy storage.

The prototype battery, about the size of a hockey puck, uses molten salt technology to trap and store energy.

The work by the Pacific Northwest National Laboratory (PNNL) scientists was published online March 23 in Cell Reports Physical Science.

“Longer-duration energy storage technologies are important for increasing the resilience of the grid when incorporating a large amount of renewable energy,” Imre Gyuk, director of energy storage at the Department of Energy Office of Electricity, said in a statement. “This research marks an important step toward a seasonal battery storage solution that overcomes the self-discharge limitations of today’s battery technologies.”

A seasonal battery could be used to capture the hydroelectric energy of spring water runoff and store it for use when summer electricity demand is high, or it could be used to enhance a utility’s ability to weather a power outage, the PNNL scientists said.

“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,” Minyuan “Miller” Li, a postdoctoral researcher at PNNL and first author of the report, said in a statement.

The freeze-thaw battery is charged by heating it to 180 degrees Celsius (356 degrees Fahrenheit, allowing ions to flow through the liquid electrolyte to create chemical energy, and then colling the battery to room temperature, which causes the electrolyte to solidify. When the energy is needed, the battery is reheated and the energy flows.

The battery’s electrolyte is molten salt, which is liquid at higher temperatures but solid at room temperature. In tests, the PNNL freeze-thaw battery has retained 92 percent of its capacity over 12 weeks.

The prototype battery was designed to avoid the use of rate and highly reactive materials and, instead, uses an anode and cathode that are aluminum and nickel, respectively, in a molten salt electrolyte with the addition of sulfur to enhance the battery’s energy capacity. And the separator between the anode and the cathode is made of fiberglass instead of ceramic, which can be susceptible to breakage during the freeze-thaw cycle.

The prototype battery’s energy is stored at a materials cost of about $23 per kilowatt hour (kWh), which was measured before a recent jump in the cost of nickel, PNNL said.

The PNNL team said it is exploring the use of iron, which is less expensive, in hopes of bringing the materials cost down to around $6 per kWh, roughly 15 times less than the materials cost of today’s lithium-ion batteries.

The prototype battery’s theoretical energy density is 260 watt-hours per kilogram, which is higher than current lead-acid and flow batteries.