[ad_1]
Artist’s rendition of the eFlyer800, Bye Aerospace.Bye Aerospace
This story was first published by Wired and is reproduced here as part of the Climate Desk collaboration.
A few years back,Venkat Viswanathan began feeling a bit existential as he drove on an interstate from Pittsburgh to San Francisco. His trip was going smoothly—almost too smoothly, he thought. He would drive for only a few hundred miles, stopping for food or to enjoy the beautiful early summer scenery. It was the classic Great American Road Trip. It was not surprising that he did it in an electric vehicle.
Viswanathan, a scientist at Carnegie Mellon University, is an expert in high-energy-density batteries—designs that are meant to pack a lot of juice into not a lot of space. This involves chemistry that can feel almost absurd at times; the unobtanium nature of battery tech. He began to explore other applications for his work after that summer of being propelled across-country by a fully obtainable battery. “I was like, ‘Wait, what am I doing with all these new batteries I’m inventing?’” Viswanathan recalls. “Who is going to need them?” There was another way to travel coast-to-coast, he realized, one that batteries were far from decarbonizing: flight.
The battery industry has seen a steady growth over the past few years. Cars are the main focus of this article. yielding steady, incremental improvements to a particular scientific approach. This involves lithium ions that move between a cathode composed of a few metal oxides—including nickel, cobalt, manganese, and iron—and an anode made of graphite. This is a classic recipe that has been quite successful. Recently, lithium-ion batteries have pushed the range of passenger cars past 400 miles—about as good as many combustion engines, and enough to overcome the “range anxiety” that might make some drivers reluctant to go electric. But as they approach the theoretical limit of how much energy they can store, lithium-ion batteries remain well short of what’s required for most aircraft.
The aviation industry has been struggling with this problem for a while. The industry contributes about 2 percent of global carbon emissions—a relatively small figure, but one that is poised to grow sharply as more of the world takes to the skies. Only one in 10 people takes a flight each year. a 2018 study estimated that 1 percent of the world’s population is responsible for half of aviation emissions.) Viswanathan believes that batteries will need to be rethought if those planes are going electric. Even regional jets for short hops need batteries that are lightweight but powerful enough. They must have enough power to takeoff and enough energy to safely cruise long distances. It’s possible that it will never be practical—and that greener aviation will require other approaches, like hydrogen or synthetic jet fuel.
Or by rethinking the fundamentals of battery technology. Viswanathan was last week with other aviation and battery experts. Published in Nature what he considers a “wake-up call” to the industry to invest in basic science beyond moving around lithium ions. The authors advocate for new cathodes made from more exotic materials. These are called conversion reactions and can move more electrons, potentially delivering more energy. It’s stuff that people haven’t really considered since the 1970s, when cobalt started to win out. The US Department of Energy has set a goal to build a battery that can store 500 watt-hours of electricity per kilogram. Viswanathan and his coauthors think that for a workhorse of the skies, like the Boeing 737, we’ll need to double that, and we’ll need new chemistries to get us there. “We’re trying to move the goalpost,” he says.
The chemical love story between the lithium-ion and lithium-ion batteries is one of their most important. Once separated by a charge, lithium ions and electrons always seek to reunite. This is how a current is generated by the wandering of electrons across a battery. However, lithium is limited in this sense because it only has one electron to give up. In theory, more electrons could mean more energy. This is something that other elements may be able to offer. You can get more electrons buzzing by using iodine, sulfur, or fluorine.
But there’s a wrinkle in this plan. Current batteries have the wonderful feature that lithium ions can move backwards and forwards without causing any trouble. They’re caught and released by the cathode—a process called insertion—but once inside of it, the ions don’t react with the other materials and reorganize the atomic arrangements. For some other elements, that’s not the case. “We have new materials that weren’t there to begin with,” says Esther Takeuchi, a battery scientist at SUNY Stony Brook. Hence the term “conversion reaction.” These chemical reactions are complicated, and they result in electrochemical changes, as well as changes in volume. The biggest problem is getting these types batteries to recharge. Once you’ve changed what’s inside a battery, it can be difficult to return to the materials that were there before.
For the kinds of batteries Takeuchi works on, recharging isn’t typically necessary. Her specialty is packing lots of energy into small spaces, like medical devices, that need to last a long time on a single charge—a lifetime even, because a recharge or battery swap might require surgery. Vanadium is a common component of pacemakers today. Her team has been studying how conversion chemistries like fluorinated carb (referred to as CFx or iodine) might work better.
The same space- and weight-saving principle applies to planes for long distances. But a battery that has only a single life won’t work for a plane that needs to recharge with every leg. Although researchers have achieved some success in the lab, they still have to deal with other problems. One of the contenders that’s furthest along is the lithium-sulfur battery—a highly desirable chemistry because of how cheap and plentiful sulfur is. Unsavorable reactions can occur between sulfur at the anode or in the electrolyte. This can lead to chemical buildup and a decrease in the battery’s ability to recharge. Sometimes, those reactions form a pesky thing called a dendrite—a vein of material in the electrolyte that gradually extends and may eventually connect the anode and the cathode, causing a short-circuit—and a fire.
Conversion reactions require a lot more chemistry than usual, but Takeuchi points out they don’t completely abandon the path that batteries have taken. The success of any new cathode chemistries depends on near-term battery capacity improvements, such as new materials anodes. Other than graphite.
One of those is lithium-metal. Graphite was a good choice for its stability. However lithium metal has better electrochemical properties and takes up less room than other designs. Cuberg CEO Richard Wang claims that the company’s lithium-metal batteries are 70% more efficient than conventional designs. Northvolt, a Swedish manufacturer of batteries, recently acquired Cuberg. Wang chose to focus his startup in the aviation industry as it would be more interested in energy density improvements. The company’s idea is to power relatively small aircraft; they have partnered with startups that want to make vertical liftoff vehicles that can operate over a short range.
It’s possible those lithium metal anodes could be paired with more experimental cathode chemistries to power larger aircraft, but the path is uncertain, Wang says. It’s a classic pickle: Plane makers want certainty that big-leap technologies will work out, while the battery startups (and their potential funders) need assurances that their experiments will eventually have a use. He believes that bigger planes might be less useful to electrify. They might choose to stop using batteries for short regional routes. Hybrid approaches might be an alternative for longer routes where batteries are not practical. In these cases, a gas engine will take over from takeoff to landing. Greener jet fuelsIf the infrastructure is put in place, and a greener way to produce it, then hydrogen. No one knows where to place their bets yet.
George Bye, the founder of Bye Aerospace, calls that the “white space” of electric plane innovation. He draws a clear line of progress for small-sized lithium-ion batteries to power small electric aircraft like the two- and 4-seat training planes his business builds. Then he draws a line of progress in lithium-metal and other almost there innovations. Like solid-state batteriesThis will increase the range and capacity of electric aircraft. Then, after that—who knows? White space. His company has explored lithium sulfur for larger aircraft but it is not yet ready for prime-time. “It’s a little bit behind,” he says; one partner working on the technology recently went bankrupt.
Bye believes that there is one silver lining: the plane can be designed to move more efficiently in the air because it has a simpler jet engine. This increases the range and passenger capacity. “It’s not apples to apples, as some people like to say,” he says. The company is also working towards FAA certification for its training aircraft so it can start delivering the hundreds orders it has received form airlines and flight schools. Among the challenges is proving that the plane can handle fire risks—a matter not just of chemistry, but the structural design of the battery packs—and still pull an emergency landing even if a battery blows.
Large electric planes equipped with revolutionary batteries could be decades away. But Takeuchi maintains that there is “room for optimism” for battery-powered jets. “Sometimes people ask if this is even possible in our wildest dreams,” she says. “And when we look at the materials and we look at the numbers, we say, ‘Yeah, it is.’” She and her coauthors point out that the future of aviation was initially electric. In 1884, the first round-trip flight by an aerial vehicle—the airship *La France—*flew by the power of a massive zinc-chlorine battery. She believes electric is ready to make a comeback nearly a century and half later.
