Half a century ago, the battery of the future was built out of sodium. The reason has to do with why the seas are salty. Sodium is a light element that ionizes easily, giving up one of its electrons. In a battery, those ions shuttle back and forth between two oppositely charged plates, generating a current. This looked like a promising way to power a house or a car. But then another element crashed the party: lithium, sodium’s upstairs neighbor on the periodic table. In 1991, Sony commercialized the first rechargeable lithium-ion battery, which was small and portable enough to power its handheld video cameras. Lithium was lighter and easier to work with than sodium, and so a battery industry grew up around it. Companies and research labs raced to pack more energy into less space. Sodium faded into the background.
So it was surprising this summer when China’s CATL, one of the world’s largest battery makers, announced sodium would play a role in the electrified future. CATL, like its competitors, is a lithium company through and through. But starting in 2023, it will begin placing sodium cells alongside lithium ones inside the battery packs that power electric cars. Why? Well, for one thing, a CATL executive pointed out that sodium is cheaper than lithium, and performs better in cold weather. But it was also hedging against an issue that was difficult to imagine in 1991. By the end of this decade, the world will be running short on the raw materials for batteries—not just lithium, but also metals like nickel and cobalt. Now that electrification is actually happening on a big scale, it’s time to think about diversifying. A CATL spokesperson tells WIRED it started thinking about sodium 10 years ago.
CATL’s announcement “really injected new energy into the people who work on sodium,” says Shirley Meng, a battery scientist at the University of California, San Diego who works extensively with both elements. As a young professor, Meng started working with sodium in part because she was looking for a suitably weird niche to stand out in—but also because she believed it had potential. “The biggest barrier to success for sodium was that lithium was so successful,” she says.
Lithium is not exceptionally rare. But deposits are concentrated in places that are hard to mine. So companies like CATL compete to secure a slice of the supply from a limited number of mines, mostly located in Australia and the Andes. Meanwhile, reserves in North America are tied up in environmental disputes, raising concerns in the US about the security of the supply chains. Competition is even fiercer for nickel—which Elon Musk has called the “biggest concern” for the future of EV batteries, due to price and supply constraints—and for cobalt, 70 percent of which is dug up in the Democratic Republic of the Congo.
As more mines open, there will probably be enough lithium to power all the world’s vehicles, Meng says. But that doesn’t account for all of the things poised for electrification that aren’t cars: chiefly, the batteries that will manage the load within microgrids and keep our lights on at night when the rooftop solar panels are in the dark. Those are the kinds of applications Meng had in mind when she got into sodium research. “I was thinking everybody would have a refrigerator for electrons in your home in the same way you have a refrigerator for food,” she says. “I think that really is the vision for grid storage.”
Sodium is a common element that’s usually mined from soda ash, but it can be found basically anywhere, including in seawater and in peat from bogs. It also happens to be well-suited to the kinds of applications Meng is describing. The ions are a little heavier and bigger than those of lithium, meaning you can’t pack as much energy into a small space, like the belly of a car. “Where sodium batteries can make a big impact is on the grid,” explains Nuria Tapia-Ruiz, a professor at Lancaster University and director of the Faraday Institution’s sodium battery initiative. Those batteries can be a little bigger, a little heavier, but it doesn’t matter because they just need to sit tight.
Historically, Tapia-Ruiz says, sodium batteries have been held back in part because of chemical stability. While sodium and lithium are periodic neighbors, they exist in parallel universes of chemistry, reacting differently with various elements and compounds. This means switching to sodium requires developing novel materials for the battery’s cathode and anode, the positive and negative electrodes that capture and release ions as the battery is charged up and then spent. One particular trouble is that chemical reactions inside the battery can eat away at the electrolyte that sits between the electrodes, reducing battery life or risking the creation of sodium metal, which can be explosive. Another challenge is that energy-dense sodium batteries typically contain nickel, as do many lithium batteries. Eliminating that metal is a key concern for researchers, though difficult. “But that's the right thing to do because you want to create a technology that is sustainable and very green,” Tapia-Ruiz says.
But the handful of labs and startups still working with sodium have made quiet progress in recent decades. Natron, a California-based startup, builds sodium batteries primarily for backup power at industrial facilities and data centers. The company uses a material called Prussian blue as the basis for its electrodes, a variation of the early synthetic pigment used in iconic paintings, including Under the Great Wave Off Kanagawa. Inside a battery, the design is not especially energy-dense, even by sodium standards. But one advantage, according to Jack Pouchet, the company’s vice president of sales, is that “Our supply chain could be local.” It contains common elements like sodium, manganese, and iron, and the factory is in Santa Clara, California. For what it lacks in energy storage, the battery can charge and dispense that energy fast. Oomph over range. The company hopes its batteries can be used to quickly charge electric cars when the power grid is stretched thin. Natron is moving ahead with plans to install such devices in San Diego, Pouchet says.
The company’s other pitch is safety. Pouchet points to incidents at grid battery storage operations, including a major fire at a battery facility in Australia and overheating at another installation in California, as raising concerns about the advisability of putting batteries in everyone’s house, however rare those fires might be. “I wouldn’t want to have that in my garage,” he says. The company’s website features demonstration videos of crushing and heating the battery packs and shooting them with a gun, all without apparent issues.
But, in general, the safety of sodium batteries is “not perfect,” Meng says, and it depends on the specific battery design. It all comes down to pairing the right cathode and electrolyte—and eliminating fire risks is more difficult for more energy-dense batteries, like those found in cars, or those designed to dispense energy over a longer period of time, like grid storage batteries.
CATL, too, says its sodium designs are safe, in addition to offering higher energy density with a nickel-free cathode. The battery is comparable, the company claims, to lithium-iron-phosphate, or LFP batteries, which are increasingly popular in mid-range cars. CATL also compensates for the lower energy density by pairing the sodium batteries with lithium-based cells. The company has said its goal is to make the two elements largely interchangeable in the manufacturing process as well, slotting sodium alongside lithium in its large and complex supply chain.
That’s a big deal, explains Meng, because any cost comparisons between sodium and lithium designs will depend on scaling up sodium battery production. That depends on big manufacturers like CATL. Wood Mackenzie, a consultancy that focuses on natural resources, estimates sodium batteries will cost 40 percent less to make than LFP batteries, largely because of the cheap materials—but only once sodium production is scaled. The firm says lithium is expected to remain dominant for years to come.
Meng points out that technologies like sodium—and other lithium alternatives, which include zinc and vanadium—are also an opportunity for places like the US, which lacks an extensive battery industry, to build one. Meng and other UC San Diego researchers recently launched an initiative to set up manufacturing techniques for solid-state sodium batteries, a next generation of technology that would be far safer and more energy-dense than the batteries we have now. It’s a long way off—researchers and startups are struggling to commercialize solid-state lithium batteries, and sodium versions have received far less funding and attention. But it’s well worth planning for the future, she adds—and continuing to work with the underdog. “There’s still a lot more exciting discoveries that can be made,” she says.