This startup sees a need for aviation-specific batteries
By Paul Brinkmann|June 6, 2023
Competition grows for higher-energy, lower-weight batteries
When an electric car accelerates from a stoplight, the drivetrain suddenly demands more power from the car’s lithium-ion battery pack, until it gets to its cruise speed.
But the drain on the battery pack in that case pales in comparison to when an electric aircraft takes off vertically. The situation is even more challenging when the time comes to land vertically under rotors, since the battery pack has been at least partially depleted from the flight.
Such unique demands have inspired engineers in the U.S. and abroad to seek more powerful and energy dense power sources. One of them is Venkat Viswanathan, an associate professor of mechanical engineering at Pittsburgh institution Carnegie Mellon University, who will join the University of Michigan’s aerospace engineering department in August.
I spoke to Viswanathan about And Battery Aero, the company he started last August in Silicon Valley to perfect and commercialize a new lithium-ion battery technology he helped develop with grants from the U.S. Department of Energy.
Specifically, the new design saves weight by replacing graphite in the battery anode, which is the electrode that releases ions, with lithium metal. A battery pack could comprise thousands of cells, each with its own anode, so the weight savings could add up significantly and propel an aircraft farther on a given amount of charge.
Viswanathan calls the pursuit of better batteries “the problem of our generation,” given the need he sees to transition from fossil fuels to electricity to avoid the worst effects of climate change.
Such advances in battery technology are crucial to “meet the sustainability challenge of the emissions associated with regional and narrow-body aircraft, and also to enable [any] aircraft with advanced batteries to reach longer ranges.”
Regarding an electric vertical lift aircraft, once it has achieved altitude and moves horizontally, it can at times depend solely on aerodynamic forces for lift, much like a car can coast downhill. But the range or distance these aircraft can fly will also depend on sustained power output.
Because battery weight is a crucial factor for electric aircraft performance, the aviation industry often refers to the battery power available for takeoff and landing in terms of specific power, which is generally measured in kilowatt-hours per kilogram of battery weight.
However, when measuring the battery capacity available over the duration of a flight, the aviation industry favors specific energy (measured in watt-hours per kilogram), a form of the more widely used term, energy density, which expresses energy per liter of battery volume.
Viswanathan says his lithium metal cells produce specific energy at 400 Wh/kg of battery weight and specific power of greater than 1 kW/kg. The best batteries in the car industry have a specific energy of around 300 Wh/kg, although that number changes regularly as better batteries emerge.
Viswanathan’s battery innovation provides significant advances in both specific power and specific energy, whereas others often sacrifice one attribute for the other, he says. The emphasis on both is where the “and” in the company name comes from.
“Currently, all of the eVTOL [electric vertical takeoff and landing aircraft] makers are just taking automotive cells and packing them together, but soon they will have to diverge and use their own custom cells for their specific requirements,” Viswanathan says.
Viswanathan and And Battery co-founder Shashank Sripad, together with Massachusetts battery manufacturer 24M Technologies, have obtained $11.9 million in additional grants from the Department of Energy’s Advanced Research Projects Agency-Energy. The two companies are working out plans to produce batteries commercially using And Battery’s proprietary lithium metal technology.
Viswanathan knows others are approaching aircraft battery innovation with different materials and engineering solutions, including China-based CATL, one of the world’s largest manufacturers, and California-based Amprius Technologies.
Amprius announced in March a battery with a specific energy of 500 Wh/kg and an energy density of 1,300 watt-hours per liter, achieved by replacing graphite anodes with silicon anodes.
According to Viswanathan, the Amprius approach “is certainly quite attractive” and “one of the best silicon-based approaches to achieving aviation-grade batteries.” But he says reliance on silicon “will always end up being lower in specific energy versus lithium metal.”
CATL in April announced development of a “condensed battery” with an energy density of 500 Wh/kg that it says it can begin mass producing “in a short period of time.” The company said the design could open up “brand-new electrification scenario of passenger aircrafts.”
However, the company did not respond to my attempts to reach it for more details. “We need more information before we can assess the CATL claim. At this stage, there is not much data, so it’s difficult to tell,” Viswanathan says.
His strategy of replacing graphite with lithium increases the amount of lithium per battery cell, but also results in a more efficient battery pack and means the pack could be smaller, he says, so the total amount of lithium involved doesn’t have to increase.
Viswanathan says nickel shortages are a bigger problem for the battery industry, but he doesn’t expect that to affect development of his technology in the near term.
He says his battery cell technology is now “reasonably well validated,” but “now we need to scale the number of layers of the cell, and then put them together in a module to test the whole battery system.”
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