Energy Storage

PNNL Tests Show Promise For Low Cost, Long Duration Sodium Battery

A new battery design shows promise to deliver longer duration with lower costs and safer materials, according to a new report from the Pacific Northwest National Laboratory.

The report, published this month in Energy Storage Materials, tested a small, coin shaped sodium-aluminum battery. Adena Power, supplied PNNL researchers with their patented solid-state, sodium-based electrolyte to test the battery’s performance.

“Our primary goal for this technology is to enable low-cost, daily shifting of solar energy into the electrical grid over a 10- to 24-hour period,” Vince Sprenkle, a PNNL battery technology expert, said in a statement.

The test showed that the new molten salt battery design has “the potential to charge and discharge much faster than other conventional high-temperature sodium batteries, operate at a lower temperature, and maintain an excellent energy storage capacity,”

Guosheng Li, a PNNL materials scientist and the principal investigator of the research, said in a statement. “We are getting similar performance with this new sodium-based chemistry at over 100 °C [212 °F] lower temperatures than commercially available high-temperature sodium battery technologies, while using a more Earth-abundant material.”

Because the new design operates at a lower temperature, it can be manufactured with inexpensive battery materials, instead of requiring more complex and expensive components and processes as in conventional high-temperature sodium batteries, David Reed, a PNNL battery expert and co-author of the study, said in a statement. The PNNL researchers estimated that a sodium-aluminum battery design could cost as little as $7.02 per kilowatt hour for the active materials.

The new sodium-based molten salt battery uses two distinct reactions. The PNNL team previously reported a neutral molten salt reaction. The new discovery shows the neutral molten salt can undergo a further reaction into an acidic molten salt that increases the battery’s capacity, the researchers found. Specifically, they reported that after 345 charge/discharge cycles at high current, the acidic reaction mechanism retained 82.8 percent of peak charge capacity.

The tests showed that new battery design could deliver up to 11 watt hours per kilogram (Wh/kg) of discharge energy. Lithium-ion batteries used in commercial electronics and electric vehicles typically deliver an energy density of about around 170–250 Wh/kg.

However, the new sodium-aluminum battery is inexpensive and easy to produce in the United States from much abundant materials, the PNNL researchers said. It uses sodium, which is relatively abundant, and aluminum wool, a manufacturing byproduct.

The new design is a variation on the sodium-metal halide battery that has been shown effective at commercial scale and is already commercially available, but with a significant change. “We have eliminated the need for nickel, a relatively scarce and expensive element, without sacrificing battery performance,” Li said. In addition, the aluminum cathode charges more quickly than nickel, which is “crucial to enable the longer discharge duration demonstrated in this work.”

State-of-the-art for grid energy storage using lithium-ion batteries is about four hours. The new design is “especially adept at short- to medium-term grid energy storage over 12 to 24 hours,” PNNL said.

The PNNL team is now focusing on further improvements to increase the discharge duration of the new battery design to improve its ability to work in coordination with renewable power sources.

“This research demonstrates that our sodium electrolyte works not only with our patented technology but also with a sodium-aluminum battery design,” Neil Kidner, a co-author of the study and president of Adena Power, said in a statement. “We look forward to continuing our partnership with the PNNL research team towards advancing sodium battery technology.”

APPA Storage Tracker

The American Public Power Association’s Public Power Energy Tracker is a resource for association members that summarizes public power energy storage projects that are currently online. The tracker is available here.

APPA Energy Storage Working Group

APPA’s Energy Storage Working Group (ESWG) is part of a cooperative agreement between APPA and the Department of Energy (DOE) Office of Fossil Energy and Carbon Management to lower barriers to integrating battery storage with the operation of fossil fuel generation assets.

In 2022, the ESWG developed a report on energy storage challenges, solutions, and opportunities for public power.

APPA is continuing to convene members to get feedback, advice, and other input on the energy storage challenges and opportunities for integrating energy storage. The next ESWG virtual meeting is scheduled for February 23, 2023, from 2 – 3:30 PM ET. The main goal for the meeting will be to discuss the baselines for an energy storage maturity model framework.

If you are interested in joining or learning more about the Energy Storage Working Group, please contact [email protected].