A few years Some time ago, while driving on an interstate between Pittsburgh and San Francisco, Venkat Viswanathan began to feel a little existential. His ride went smoothly – almost too smoothly, he thought. He would hum a few hundred miles at a time, stopping briefly for a meal or to enjoy the early summer landscape. It’s the classic Great American road trip. And there’s nothing remarkable about him doing it in an electric car.
Viswanathan, a scientist at Carnegie Mellon University, is an expert on high-energy-density batteries — designs that aim to pack a lot of juice into large spaces. At times, this involves chemistry which can feel almost fanciful; atoms of battery technology. But after that summer when he was pushed across the country with a completely purchasable battery, he began to consider another application for his work. “I was wondering, ‘Wait, what am I doing with all these new batteries I’m inventing? ”” Viswanathan recalled. “Who will need them?” He realized that there was another way to travel from coast to coast, one that batteries were far from decarbonizing: flight.
Over the past few years, the battery industry has mostly focused on automobiles, provides steady, incremental improvements to a particular scientific approach. This involves lithium ions moving between a cathode consisting of several metal oxides – including nickel, cobalt, manganese and iron – and an anode made of graphite. This classic recipe has turned out pretty well. Recently, lithium-ion batteries have pushed the range of passenger cars past 400 miles — about the same as many internal combustion engines, and enough to overcome the “range anxiety” that can make some the driver does not want to use electricity. But when they reach the theoretical limit of how much energy they can store, lithium-ion batteries still fall short of what’s needed for most aircraft.
The airline industry has struggled with this problem for a while. This industry contributes about 2% of global carbon emissions – a relatively small number, but one that is poised to thrive as more and more people around the world take to the skies. (Only about 1 in 10 people take a plane every year and a 2018 study estimated Viswanathan believes that 1 percent of the world’s population is responsible for half of aviation emissions). Even regional jets intended for relatively short hops need a light but powerful enough battery. They need enough power to take off, then enough energy to cruise safely over long distances. It’s possible that will never become a reality – and greener aviation will require other approaches, like hydrogen or fusion jet fuel.
Or by rethinking some battery fundamentals. Last week, along with other aviation and battery experts, Viswanathan published year nature what he sees as a “wake-up call” for the industry to invest in basic science beyond moving around lithium ions. In particular, the authors favor new cathodes involving more exotic materials, some of which induce transition reactions, known as transition reactions, that move more electrons and potentially pack more energy. It’s something people haven’t really considered since the 1970s, when cobalt started to lose value. The US Department of Energy project has set a goal of creating a battery that can hold 500 watt-hours of energy per kilogram. Viswanathan and his co-authors think that for a horse of the sky, like the Boeing 737, we’re going to need to double that, and we’re going to need new chemicals to get us there. “We are trying to move the landmark,” he said.
Lithium-ion battery is a chemistry love story. Lithium ions and electrons, once separated by an electric charge, always seek to recombine. The movement of these electrons through a battery cell is what generates the current. But in that sense, lithium is limited because it has only one electron. In theory, more electrons moving around means more energy, which is what other elements can provide. Try iodine, maybe, or sulfur or fluorine, and you might get more electrons.
