Supercapacitors can charge almost instantly, and discharge enormous amounts of power if needed. They could completely erase the Achilles heel of electric vehicles – their slow charging times – if they could hold more energy. And now Chinese and British scientists say they've figured out a way to store 10 times more energy per volume than previous supercapacitors.
A team split between University College London and the Chinese Academy of Sciences has released a study and proof of concept of a new supercapacitor design using graphene laminate films and concentrating on the spacing between the layers, the researchers discovering that they could radically boost energy density when they tailored the sizes of pores in the membranes precisely to the size of electrolyte ions.
Using this design, the team says it's achieved a massive increase in volumetric energy density. Where "similar fast-charging commercial technology" tends to offer around 5-8 watt-hours per liter, this new design has been tested at a record 88.1 Wh/l. The team claims it's "the highest ever reported energy density for carbon-based supercapacitors."
That figure is toward the high end of what a typical lead-acid battery stores, but while lead-acid batteries charge very slowly and offer fairly low power density, the supercapacitors can charge very, very quickly and offer massive power densities around 10 kilowatts per liter.
In addition, the supercapacitors appear to have a long service life, retaining 97.8 percent of their energy capacity after 5,000 cycles, and they're very flexible, performing almost exactly the same when bent 180 degrees as when they were lying flat.
There is a but. There is always a but. Indeed, there's three big buts here, beyond the fact that this is still at the research proof of concept stage.
The first is that these supercaps are still far less dense than a top-shelf lithium EV battery. Closest estimate I can find on what Tesla is running is a 2018 estimate of 877.5 Wh/l, which would mean a supercap would have to be 10 times the size of a Tesla battery pack to offer the same range. Not gonna happen. Mind you, EVs won't have to offer 430-mile (700 km) range figures once they're even quicker to top up than a petrol car. The vast majority of car use would easily be less than 100 miles (160 km) in a day, and a short stop every hour and a half on a long trip might be no big deal for many drivers.
What's more, we've written before about the extraordinary things you can do when you pair lithium batteries with supercapacitors in a hybrid arrangement. This kind of density development could increase the amount of supercapacitor you might be able to run in such a setup, further maximizing the benefits.
The second issue: supercapacitors tend to leak energy rather than storing it very well. You might find your EV out of power if you leave it off the charger for a week or two. Although to be fair, when they charge so fast, you might not mind.
And the third issue: this thing is made of graphene, everyone's favorite wonder-material which is set to revolutionize everything from electronics to mosquito protection to aviation to hair dye to concrete to running shoes to bulletproofing to loudspeakers and every other field it's been researched in... But to date, nobody's producing it in mass commercial quantities at a price that makes huge graphene supercapacitor cells feasible.
Still, the researchers are optimistic. “Successfully storing a huge amount of energy safely in a compact system is a significant step towards improved energy storage technology," said senior author and Dean of UCL Mathematical & Physical Sciences, Professor Ivan Parkin (UCL Chemistry). "We have shown it charges quickly, we can control its output and it has excellent durability and flexibility, making it ideal for development for use in miniaturized electronics and electric vehicles. Imagine needing only 10 minutes to fully-charge your electric car or a couple of minutes for your phone and it lasting all day.”
Oh, we're imagining, Professor Parkin, we're imagining alright. And there are numerous other uses for supercapacitors where this kind of technology could instantly shine if it makes it through to production.
The study was published in the Nature Energy journal.
Source: University College, London
By way of an example, to stop a (small) 1 tonne car in 15 seconds from 60mph (96.6kM/h) generates ~100Wh (360kJ) of energy at a rate of ~24kW, so 3 litres of the new supercapacitor could comfortably take all the braking power and release it to support acceleration shortly afterwards. Reducing the current draw from the main batteries during acceleration may also be advantageous for efficiency and battery life.
It will be interesting to see 4800v pmdc axial flux motors the size of a dinner plate that can lay down 100KW of output:-)
(Capacitors, especially large capacitors, are tremendously dangerous so make absolutely sure you know what you're doing before you ever try something like this yourself).
like this one
https://iopscience.iop.org/article/10.1088/1361-6528/aa8948
claiming a whopping 148.75 Wh kg−1