United plans to electrify airport operations with sodium-ion batteries

Gas-fueled passenger cars, school buses, lawnmowers and leaf blowers are steadily being replaced with electric versions, a transformation that’s been made possible by lithium-ion batteries. The technology tends to be lighter weight, more energy-dense and far more readily available than alternative chemistries, which have struggled to catch on and scale up in recent years.

Yet one of lithium-ion’s competitors may be poised to gain a foothold, in a market that’s ripe for electrification: airports.

On Wednesday, United Airlines said it’s investing in sodium-ion battery maker Natron Energy, as part of the airline’s larger efforts to curb planet-warming pollution across its operations. Natron’s batteries could be used to electrify ground equipment, such as forklifts and pushback tractors, and to store large amounts of renewable energy onsite — which might eventually be needed to recharge the batteries in electric passenger jets or flying taxis.

“Aviation is an emerging space for us that appears to be potentially very high-impact from a decarbonization perspective,” Colin Wessells, CEO and co-founder of Natron Energy, told Canary Media.

Sodium-ion batteries have a few key advantages over other chemistries. The salt-based battery is nonflammable and can be made from relatively cheap, abundant and nontoxic materials, including iron and manganese. The durable devices can recharge tens of thousands of times before they degrade and need to be replaced. 

And, unlike lithium-ion batteries, they aren’t at risk of experiencing thermal runaway, which happens when battery components overheat and feed off each other, causing extremely hot explosions and releasing toxic gas. Sodium-ion batteries only have about half the energy density of their lithium-ion counterparts, but that’s less of a concern for stationary applications and heavy-duty equipment that mostly stays put.

“This opens up the opportunity to safely electrify a lot of airport operations,” Wessells said of the technology.

United has recently invested in a range of cutting-edge companies with the goal of transforming its airborne fleet from oil-guzzling jets to aircraft powered by hydrogen fuel cells, batteries or alternative jet fuels made from biomass, used cooking oil and municipal solid waste. By backing Natron, the Chicago-based airline is now targeting emissions from ground operations as well.

“United is going to lead the way in decarbonizing this business, and this [investment] is another piece of that puzzle,” Michael Leskinen, president of United Airlines’ venture-capital arm, told Canary. 

Aviation contributes roughly 2.4 percent of the world’s carbon dioxide emissions every year. In the United States, a relatively tiny share of those CO₂ emissions — 1.7 percent — come from airport operations in particular, according to the Federal Aviation Administration. 

However, ground equipment still spews harmful diesel exhaust into communities surrounding airports. And electrifying buses, luggage-haulers, stair lifts and other vehicles is something airlines and airport operators can do immediately to reduce greenhouse gas emissions. United said it operates more than 12,000 pieces of motorized ground equipment, about one-third of which currently use lithium-ion or lead-acid batteries.

Natron is ​“going to provide a lower-cost battery, using materials that are domestically sourced…that will enable us to electrify equipment both grounded and in the air,” Leskinen said.

Natron and United declined to disclose the size of the investment announced this week. Wessells said his company, which is based in Santa Clara, California, has raised $155 million in total equity investment since it was spun out of a Stanford University lab in 2012. The company also received $19.9 million from the U.S. Department of Energy’s ARPA-E program to scale production.

Natron currently operates a pilot production line in Santa Clara and ships dozens of battery packs per month to data centers and other industrial customers, which primarily use the batteries for backup power. 

Its sodium-ion batteries use Prussian blue — a synthetic pigment used in paints and dyes — in both the cathode (positive) and anode (negative) electrodes. As this IEEE Spectrum article explains well, the low-cost material soaks up and releases sodium ions, which allows the battery to rapidly charge and discharge and deliver quick bursts of energy. The dark-blue electrodes can also last longer than the carbon- and metal-based electrodes in lithium-ion or lead-acid batteries.

In May, Natron announced it would begin commercial-scale production at a battery facility in Holland, Michigan, through a collaboration with Clarios International. Electrodes and cells based on Natron’s Prussian blue chemistry will be manufactured at what is now a lithium-ion battery factory.

Wessells said the latest funding from United will allow Natron to accelerate production at the facility in Michigan, which is slated to start commercial deliveries in July 2023. Still, he added, it may take several years before the sodium-ion batteries wind up in airports, owing to permitting and regulatory requirements. 

“The vast majority of research and investment dollars for batteries has really been around passenger EVs,” he said. ​“But there are all sorts of other big industries out there that need help decarbonizing their operations, and other types of batteries with other characteristics [than lithium-ion] that can have a really high impact in these other industries.”

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