Supercapacitors rely mostly on double-layer capacitance to bridge the divide between chemical batteries and traditional capacitors, but they come with a number of weaknesses. Paramount among these are their relatively low voltage of around 2.7 V before their electrolyte begins to decompose, as well as their relatively high rates of self-discharge. Here a new design using lignin-derived porous carbon electrodes and a fluorinated diluent was demonstrated by [Shichao Zhang] et al., as published in Carbon Research, that seems to address these issues.
Most notable are the relatively high voltage of 4 V, an energy density of 77 Wh/kg and a self-discharge rate that’s much slower than that of conventional supercapacitors. In comparison with these supercapacitors, these demonstrated versions are also superior in terms of recharge cycles with 90% of capacity remaining after 10,000 cycles, which together with their much higher energy density should prove to be quite useful.
This feat is accomplished by using lignin as the base for the carbon electrodes to make a highly porous surface, along with the new electrolyte formulation consisting of a lithium salt (LiBF4) dissolved in sulfolane with TTE as a non-solvating diluent. The idea of using lignin-derived carbon for such a purpose has previously been pitched by [Jia Liu] et al. in 2022 and [Zhihao Ding] in 2025, with this seemingly one of the first major applications we may be seeing.
Although the path towards commercialization from a lab-assembled prototype is a rough one, we may be seeing some of these improvements come to supercapacitors near you sooner rather than later.
For supercapacitors, that’s a poor cycle life. Note the 1000x multiplier in the Wikipedia table. Conventional supercapacitors are expected to last up to a million cycles.
But with low self discharge they don’t need to charge them as frequently. In some applications it may (partially) replace batteries. And for batteries that’s a lot of cycles.
They’re not very good batteries either for the low energy density, yet there’s the inherent risk of a high-density electrostatic device going kaboom on a short circuit.
Their energy density is getting better. Graphene supercapacitors can go up to 100 Wh/kg experimentally. Which is competitive for batteries in some scenarios.
Batteries also explode if you don’t have protection circuits. You can implement current protection for supercapacitors too.
reminds me of the recent article about how gosh darn miraculous lithium batteries are. the idea that we could look at 77Wh/kg and say “not very good” is definitely something that lithium batteries have done to our brains.
I think “about half as energy dense as lipo” is close enough that we start to look at questions like durability. Enumerated over years, charge cycles, heat exposure, electrical faults, mechanical faults. If they do much better than lithium, i could see them being quite valuable in some cases. I’d certainly accept some capacity compromise for a battery that didn’t reliably puff up if deep discharged, or never lit on fire while charging. Might even accept much less capacity if they were very quick to charge in addition to other benefits.
Can’t say whether these capacitors qualify or not. Internal resistance on a supercapacitor is, i assume, much worse than a common electrolytic, which is itself much much worse than the ideal capacitor that exists in my imagination. Protection circuits etc will also factor in… Might be much safer in a short circuit. Or might not.
The weight hardly matters if the battery isn’t going to move. The Wh/$ and W/$ are much more interesting to me in new battery chemistries, because a lot of things don’t need to be lightweight or compact, they just need to be affordable.
So far this is about 1/4 the energy density of LiPo.
Yeah… about that. Capacitors are inherently more dangerous because the energy is stored as an electrostatic charge across an insulator, not in chemical reactions. The opposite charges are physically and forcefully attracted to each other. The insulator in a capacitor is actually under tremendous physical pressure from the charges on either side. When the insulator breaks, all the energy is released at once and there’s nothing you can do to slow it down.
Think lithium battery fire, but instead of burning like gunpowder it goes up in a bang. A large high density capacitor storing significant amounts of energy is about as safe as a steam engine boiler with a plugged up pressure release valve.
I was using $25 chinese supercap module (16V 100F) as replacement for battery in my commuter vespa. It was loosing charge rather quickly, when i came back from work on friday, it was just so-so enough to start on monday. next day no problem. i did it for two weeks and it was kinda ok, i got like two and half cranks from it. when the old carburetor engine have not started the first time, the second time was kinda dramatic, third time was likely a trip to lab psu to recharge the cap for 60 seconds. luckily the old 125 honda engines are quite reliable :-D Since the capacity is rather low, some people even use these with lithium battery in parralel which provides small trickle to help with self discharge. (BTW the supercap selfdischarge current drops over time when you keep charging. But obviously comes back as soon as you cycle the thing again)
‘Super capacitors’ in general, have low max currents.
Shorting them isn’t nearly as much fun as large regular caps.
There’s a saying in the industry that you can make anything and everything out of lignin, except money.
For years we’ve heard even in Wikipedia that supercapacitors are being used in production electric cars but no one ever specifies in which EVs or by which manufacturer ! The same kind of seeming self-censorship and silence applies to Formula E and its powertrains of course…
Paul G (EVUK)
BTW if you have option to kickstart when your battery is low, this is perfect solution. since most of the time you run and start using supercap. and when it sits too long and gets self discharged, you can just kickstart by foot and it gets instantly recharged. basically you never have to buy the battery again.