Sodium-based batteries aren’t new to the energy storage market, but interest in their technology began growing in the early 2020s as the industry explores alternatives to lithium. Sodium-ion batteries behave and can be manufactured similarly to common lithium designs, so their adoption is more straightforward than other advanced technology like flow batteries. But just as there are different lithium chemistries, there are different types of sodium batteries that are more beneficial to certain use cases. Here’s an explanation of the emerging technology.
What is a sodium battery?
Sodium battery manufacturing. Credit: Peak Energy
Sodium-based batteries use abundant sodium to produce nontoxic power. They are not flammable or explosive (as long as other materials are not added to the chemistry) and can function in a wide temperature range. Sodium battery cells can also be completely drained to zero charge without damaging the system.
Sodium ions move from cathode to anode during charging, and from anode to cathode during discharging. They are manufactured similarly to lithium batteries. The cathode and anode are coated with a slurry, the cell pouch is filled with electrolytes and then the module is sealed. Sodium cell manufacturers are adopting similar form factors as lithium cells to allow for easy adoption. Sodium batteries tend to use only aluminum in their current collector designs, while lithium uses both aluminum and copper. By only using aluminum, sodium batteries should theoretically have a cheaper price.
Due to their wide temperature range of operation and their lack of fire risk, sodium batteries do not need the heating, cooling and fire suppression apparatuses apparent in lithium BESS. This makes a large-scale sodium energy storage system’s physical footprint much smaller than lithium.
What are the different sodium battery types?
Unigrid testing an NCO battery. Credit: Unigrid
There are a few variants of sodium batteries, but the three most common are NFM, NCO and NFPP.
Sodium nickel iron manganese (NFM) is most commonly compared to lithium cobalt oxide (LCO), and can be found in light e-mobility applications, like scooters and e-bikes. Just as with LCO batteries used in portable electronics like phones, NFM batteries can be dangerous and catch fire. They’re not appropriate for large-scale applications.
Sodium chromium oxide (NCO) is often compared to lithium nickel manganese cobalt (NMC). NCO has a high energy density but not an especially long cycle life. These layered metal oxide batteries may go into thermal runaway and generate oxygen as they burn, but the opportunity for that is far less than what has been shown by lithium batteries.
Sodium iron-phosphate pyrophosphate (NFPP) is typically compared to lithium-iron phosphate (LFP). They offer better cycle life and thermal tolerances, and have almost no fire risk. U.S.-based manufacturer Alsym adds a non-flammable electrolyte to its NFPP+ design to further remove fire risk. In comparison to LFP, NFPP designs have lower energy density but require less HVAC and other BESS add-ons.
Where are sodium batteries being manufactured and installed?
As with every battery product, China currently dominates production. Sodium battery manufacturing can easily be dropped into a LFP line, and many established Chinese lithium brands have already transitioned idle or excess lines in their plants to produce sodium designs. There are a handful of sodium-ion R&D efforts happening in the United States, and the battery’s abundant chemistry base, along with its lack of critical materials, means that the United States could quickly onshore manufacturing of sodium-ion energy storage systems.
Boston-based Alsym has been developing NFPP cell designs, and large-scale energy storage developer ESS recently announced it would use Alsym tech in its upcoming sodium-ion battery launch.
“Our first launch is going to be with NFPP because that’s a good technology. It follows the same characteristics that ESS has followed since its birth — no risk of fires and it’s safe,” said Randy Selesky, ESS chief commercial officer.
UC San Diego spin-off Unigrid is developing NCO cells and announced a relationship with manufacturer Syntropic Power to make sodium-ion batteries in the United States. The two companies are targeting the residential market because it’s ready for some lithium alternatives, said Unigrid co-founder and CEO Darren Tan.
A large-scale NFPP battery from Peak Energy.
“We already have water storage at home, we have food storage. I think it’s very conceivable in the next two decades that everyone may have energy storage at home, as long as the energy storage is as affordable, as safe and as reliable as a refrigerator,” he said. “This is an opportunity for sodium-ion.”
Peak Energy will open a 4-GWh annual manufacturing capacity facility in Sacramento in 2027 that will make 3.1-MWh NFPP systems. The company is using imported cells right now, but execs are shoring up other components already, said Peak chief scientist Brandon Kelly.
“You can make hard carbon, which is the anode, from almost anything. Right now, we use coconuts. We’re going to do some peach pits and other random stuff. It makes for funny supply chain conversations,” he said. “But you can make it out of coal, you can make it out of petroleum byproducts, which are things we’re good at here in the States. Even though it’s not something that is scaled today, it’s something that will be quite easy for us to do [in the United States] relative to lithium.”
U.S. companies like these would not build the manufacturing infrastructure if there wasn’t a demand for the new battery technology. Although the current install capacity may be low today, each company rep told Solar Power World that the industry is at the start of something huge.
“Last year, there was over 3 GWh of sodium produced,” Kelly said. “There’s a lot of people that feel it’s more of a lab technology, but the reality is it’s commercial-quality cells that already hit on their performance in that large format that you can get a the gigawatt-hour scale. It’s ready for prime time.”