Allison Proffitt, Editorial Director, Battery Power Online
April 19, 2018 | The opening pair of plenary talks at the International Battery Seminary and Exhibit last month juxtaposed two grand visions: Celina Mikolajczak, director of battery development at Uber, painted a picture of an urban future in which an autonomous aircraft—a cross between a helicopter and a very small airplane—carries up to five passengers between dedicated sky ports for about 60 miles. Jeff Dahn, professor of chemistry at Dalhousie University, hopes to soon understand how the battery electrolyte ages.
It was quite a dichotomy.
Dahn, a father of battery technology and research, presented his research exploring how freezing a battery can give insights into electrolyte age while keeping the battery intact. Electrolyte testing has generally been done by taking the battery apart, but Dahn wanted to see how Li-ion batteries respond to aggressive cycling without tearing one up.
His team found that freezing the battery resulted in measurable differences in liquidus temperature as the electrolyte loses Li salt. With more battery charge cycles, Li salt was lost from the electrolyte, which increased the liquidus temperature. The test, Dahn said, could be used to estimate Molarity as the cell cycles.
Dahn measured the freezing point of the batteries with an apparatus developed to perform differential thermal analysis (DTA). The DTA apparatus monitored the temperature of a sample cell and a reference cell with an electrolyte that can’t freeze during a controlled temperature scan, about one degree per minute to keep temperature consistent across the cell.
Dahn’s lab created its own DTA apparatus to run the test, but he worked in a plug for Novonix, which has a commercially-available set up that will do the same type of testing.
Dahn said DTA is applicable for any battery with a liquid electrolyte, not just Li-ion batteries. The DTA method lets researchers measure a battery, cycle it again, and re-test, Dahn said. Then researchers can better test new chemistries to eliminate salt loss in the electrolyte and liquidus change.
Airborne Futures
Celina Mikolajczak’s presentation, then, was quite a zoom out. Mikolajczak has a Tesla pedigree but her presentation fell much farther left on the hype curve.
Within two years, Mikolajczak promised, Uber Elevate will be offering demonstration flights in their electric vertical takeoff and landing aircraft (eVTOL). Within five years the company plans to have commercial launch of commuter flights in Dallas, LA, and one other city. With a price to the consumer on par with an UberX, a VTOL could take passengers from San Francisco to San Jose in about $15 minutes. By 2025: hundreds of aircraft per city and tens of thousands of passenger trips each day, and 2030 to 2035 should see full-scale operations.
But somewhere after the slick visionary video and the bold target dates, Mikolajczak slips in a key hurdle: the batteries Uber needs for an eVTOL don’t exist yet.
We’d need a new chemistry with new cells, she said. It needs to be a Lithium metal rechargeable cell with an energy density of 400 Whr/kg. (For reference, Tesla batteries have about 254 Whr/kg. Elon Musk said back in 2014 that 400 Whr/kg was the energy density goal for a battery powering “a compelling aircraft.”)
That’s not all, of course. Uber needs the aircraft themselves, which should be capable of vertical flight (the helicopter part) with the speed and energy of a fixed-wing aircraft (the plane part). Uber needs Sky Ports in cities and flight paths for which the noise of the aircraft will “blend into the soundscape.” The aircraft must charge quickly—ideally a five-minute charge between flights that would sustain an aircraft through rush hour.
There are big safety concerns as well. Uber needs new levels of redundancy and reliability. “Running out of power in a vertical descent is much worse than running out of power on the highway,” Mikolajczak said. There will be battery fires, Mikolajczak conceded, and the new battery chemistry must be such that even if the fires are not fully contained by water, if a local fireman douses the flame with a hose, it certainly shouldn’t make the situation worse.
And Uber will need new regulations. Because the imagined aircraft are neither fixed-wing nor rotor aircraft, existing regulations don’t quite fit. Uber is working with the FAA to find a pathway that makes sense, Mikolajczak said.
It’s a vast wish list for demonstration flights planned for 2020. But Mikolajczak is hopeful. Uber hosted an Uber Elevate conference in Dallas in 2017 and has another planned for LA next month. The company has assembled a team of experts that hail from Tesla, NASA, academia and more and is still hiring. Uber sees clear skies ahead, even if the International Battery Seminar audience was a bit incredulous.
