The electric flying car is really two innovations in one, and could remain in the realm of fiction alongside the existing batteries. However, using newly developed fast-charging lithium-ion cells, such a four-wheeler could travel up to 80 kilometres.
The development of urban air mobility is unstoppable, with dozens or more of eVTOL aircraft being developed, large networked urban air mobility providers being prepared, and a series of test operations already underway in the most advanced cities. The Munich-based consultancy Roland Berger’s 2020 report counts 95 ongoing eVTOL projects around the world.
The comfort of helicopters, combined with the efficiency of aircraft and the low noise and environmental impact of electric propulsion, will undoubtedly be the air transport of the future. And of course there is the century-old science fiction topos, the flying car.
For example, Csao-Jang Wang, an automotive, mechanical, chemical and materials engineer. He is well aware of the many demands that the industry places on batteries for electric aircraft. Their weight, power and energy density are critical characteristics. They need to be fast and frequently rechargeable to generate adequate revenue, which will set back the astronomical cost of their development.
“On average, we can estimate that each of the air taxi services that rely on them would need to fly at least 15 trips a day in the morning and another 15 in the evening, with three to four people on board, covering a distance of roughly 80 kilometres,” said the lead author of the new research, Csao-Jang Wang, director of the Electrochemical Engine Center (ECEC) at Pennsylvania State University.
Wang and his colleagues have created a prototype battery that can enable eVTOL journeys of up to 80 kilometres with an energy density of 271 watt-hours per kilogram. The new lithium-ion batteries allow for more than 2,000 rapid recharge cycles over their lifetime and can be recharged in just 5 to 10 minutes.
“The first generation of commercially viable flying car batteries is now available,” Wang said.
Scientists have placed 10 micron-thick nickel foils in the battery to help it reach 60 degrees Celsius quickly. Heating the batteries can help fast charge them without the risk of destructive lithium spikes.
“Our self-heating technology has a heating rate of 1 to 5 degrees Celsius per second and consumes 0.8 per cent of battery energy for every 10 degrees Celsius rise in temperature. At the same time, the embedded nickel foil adds less than 1.5 percent extra weight and volume, and costs less than 0.3 percent compared to the basic batteries,” Wang added.
Development has not stopped there, of course, with even higher energy density battery solutions on the horizon. The next generation could offer energy densities of 350-400 watt-hours per kilogram, and costs could be reduced to $50 per kilowatt-hour, while keeping charging times at 5-10 minutes.
“This will be the second generation, which will enable not only eVTOLs for the commercial fleet, such as flying taxis, but also privately owned flying cars. My dream is to drive a flying car to work before I retire,” Wang outlined. The researchers published their findings in the scientific journal Joule.