A team of engineers at Pennsylvania State University has designed a battery prototype that they say could be the key to making flying cars commercially viable.
Published in the journal Joule, the new research appears to solve many of the problems involved in powering electric vertical take-off and landing (eVTOL) vehicles.
‘I think flying cars have the potential to eliminate a lot of time and increase productivity and open the sky corridors to transportation,’ said a member of the team, Chao-Yang Wang, director of the Electrochemical Engine Center at Penn State. ‘But electric vertical take-off and landing vehicles are very challenging technology for the batteries.’
‘Batteries for flying cars need very high energy density so that you can stay in the air,’ said Wang. ‘And they also need very high power during take-off and landing. It requires a lot of power to go vertically up and down.’
The researchers tested two energy-dense lithium-ion batteries that could be recharged with enough energy for an 80-kilometre eVTOL trip in only five to ten minutes.The batteries were capable of sustaining more than 2,000 rapid charges over their lifetime.
Flying car batteries have one unusual requirement – they must always retain some charge because power is needed so that the car can stay in the air and land.This makes recharging the batteries more problematic, because the internal resistance to charging increases as the charge in the battery increases. In order for flying cars to be commercially viable as taxis, they will also need to be able to recharge rapidly so that they can maximise revenue during rush hours.
The researchers discovered that the key is to heat the battery in order to allow rapid charging without the formation of lithium spikes that damage the battery and are potentially dangerous. They incorporated a nickel foil that can rapidly heat the battery to 60C. By heating the battery, recharging remained within the five-to ten-minute range. Heating the battery also allowed it rapidly discharge energy during take-off and landing.
‘Under normal circumstances, the three attributes necessary for an eVTOL battery work against each other,’ Wang said. ‘High energy density reduces fast charging and fast charging usually reduces the number of possible recharge cycles. But we are able to do all three in a single battery.
‘I hope that the work we have done in this paper will give people a solid idea that we don’t need another 20 years to finally get these vehicles,’ he continued. ‘I believe we have demonstrated that the eVTOL is commercially viable.’