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To create large-scale grid energy storage that is more affordable, powerful and safe, researchers at the Department of Energy’s (DOE) Oak Ridge National Laboratory (ORNL) decided to let a strong side reaction step into the limelight.

The team was developing a better battery using abundant salt water as a key component. At first, they were focused on improving a weak oxygen reaction. But they discovered that an “unwanted” side reaction was a better choice to take center stage. The research was pursued in collaboration with industry partner Coulomb Technology, which plans to commercialize the innovation.

This is the latest advance in a variety of approaches by ORNL researchers to create better energy storage that helps utilities meet electricity demand, reduce energy costs and keep power flowing during outages for a more resilient U.S. electric grid.

Today, most grid energy storage relies on banks of lithium-ion batteries - larger versions of the kind used in vehicles. But they require cooling to avoid fire risk and depend on rare materials such as lithium and cobalt imported from other countries. ORNL researchers are focused on incorporating affordable, abundant materials and designs that can safely store energy for longer periods.

Packing More Energy with Fewer Supply Chain Bottlenecks

Batteries work through electrochemical reactions that move ions between two electrodes, called the anode and cathode, through a conductive material called the electrolyte. One alternative to lithium-ion for stationary storage is to use salt water for the electrolyte. Salt water is easily available, naturally safer, and provides built-in cooling. It also avoids the need for critical materials in the electrodes.

However, salt water batteries generally rely on a sluggish chemical reaction, which converts oxygen back and forth between liquid and gas forms. These phase changes take extra energy and time. The reaction also needs a catalyst to speed it up and a constant supply of oxygen. Together, these factors add complexity and limit power output.

ORNL researchers recently discovered that before the oxygen reaction begins, a side reaction occurs that produces sodium hypochlorite - commonly known as bleach. Most researchers treat this reaction as a problem to suppress. But under the direction of ORNL lead researcher Ruhul Amin, ORNL postdoctoral researcher Wooseok Go saw an opportunity. When he realized that the strong side reaction happens first, he thought: Why fight it?

“I said, ‘Why don’t we just make the side reaction the dominant reaction, because it shows higher voltage than the oxygen reaction?’” Go said. Adding just 5 percent more bleach made the side reaction the star. Battery efficiency increased because the entire chlorine reaction occurs in liquid, eliminating the gas conversion step and the need for a catalyst. The new battery also showed less internal resistance, improving efficiency.

Switching to a chlorine-bleach reaction more than doubled the battery’s peak power and made the voltage comparable with lithium-ion batteries.

Amin said the ORNL battery also remains stable even when energy is needed quickly, as during a power outage. “It’s like the difference between hitting the gas in a sports car compared to a sedan,” he said. “It’s important how rapidly and steadily we can access the power at different levels.” He said this type of salt water battery would work well for nautical applications, since ships need fast access to power while benefiting from an abundant supply of salt water.

Next Steps for Long-Term, Large-Scale Energy Storage

Beyond the electrolyte, Go and Amin are also exploring changes to the anode metal to provide manufacturing and safety advantages. The next step is to further refine the electrodes, including modifying the positive electrode to further suppress the oxygen reaction.

Based in Tennessee, partner Coulomb Technology focuses on sodium-ion batteries for a range of grid storage applications. “This battery will round out our portfolio by serving longer-duration utility or large data center applications,” said Tim Vosburgh, Coulomb founder and CEO. “We’re extremely excited to use safer materials that can be easily obtained and deployed to deliver low-cost batteries with very competitive energy density and duration.”

Vosburgh is a graduate of ORNL’s Innovation Crossroads, one of four nodes of DOE's Lab-Embedded Entrepreneurship Program, a fellowship program for start-up founders to work with national lab experts to de-risk new energy and manufacturing technologies. Coulomb staff have been able to consult with ORNL experts and hone battery chemistries in ORNL’s Battery Manufacturing Facility.

This research was funded by DOE’s Advanced Materials and Manufacturing Technology Office through its Technology Commercialization Fund. Ilias Belharouak, corporate fellow and head of ORNL’s electrification section, also contributed to the project.

Oak Ridge National Laboratory