About 5 years ago I saw a NASA demonstration of batteries made from capacitors that were lightweight and charged very quickly. They were roughly the size of C cell batteries and were demo’d in a cordless drill.
The storage capacity was less than a NICAD but since they fully charged in a couple of minutes they appear to be a useful replacement battery. The problem is that I can’t find them and was wondering if there is a special name for them.
I would guess the limiting factor is the length of time they can hold a charge. I’m pretty sure a lot of progress has been made and shopping search for the alias on Google turns up some results. IDK.
These are 3 volts, 3000 farads. (Not 3000uF. Not 3F. That’s 3000F) 11 kilojoules. Carbon w/Acetonitrile electrolyte. Takes 16 seconds to charge at 500 amps.
One advantage to supercapacitors isn’t their ability to store charge indefinitely, but to replace rechargeable batteries.
Rechargeable batteries “age” with use and lose their ability to be recharged. Worse, in things like hand-crank flashlights, there’s a circuit to prevent overcharging. When your flashlight’s off, this stays connected and slowly drains the battery. so when you pull out that emergency hand-crank flashlight, it’s dead. Even worse, it either takes forever to re-charge with the handcrank, or can’t be recharged once it’s fully drained*. And you can’t easily take out the battery and replace it**. your 'perpetual" flashlight is actually worse than a standard battery-powered one.
None of these problems exist with a hand-crank flashlight that uses a supercapacitor in place of a battery. So far they haven’t determined a limit for the number of times it can be used. It can be completely drained and rapidly re-charged. You can throw it in your drawer or glove compartment and forget about it, then pull it out in an emergency, rapidly charge it, and have it work. The fact that it doesn;t hold the charge indefinitely is irrelevant.
Unfortunately, there’s only one such flashlight on the market. I’ve bought one, and it works very well. I’ve also bought some 1 F supercapacitors and replaced the batteries in my old (rechargeable battery-using) hand-crank flashlights, and they work very well now, too.
*Some rechargeable batteries are supposed to be drawn completely down and recharged every now and then, but the ones used in most hand-crank flashlights aren’t this sort. If you draw them com0pletely down, it’s practically impossible to recharge them.
**not only do you have to take out screws and disassemble a mechanism full of small parts that tend to fall off and roll under things, the batteries in every one i’ve taken apart have been spot-welded into place in a surprisingly flimsy holder. they aren’t made to be disassembled and have the batteries replaced. Some of them aren’t made to be disassembled at all, and there are no breaks in the outer cover.
Supercapacitors aren’t a drop in replacement for chemical cells as their terminal voltage droops as they are discharged, whereas something like a NiMH cell could start off fully charged at about 1.3 V, and still be at a useful 1.0 V when the charge is down to 10%. A capacitor charged to an initial 1.3 V will have a paltry 0.13 V available when discharged to 10%.
Supercapacitors are great, and they certainly have their uses, but don’t sell your Duracell shares just yet.
Indeed, 11 kJ is plenty. I was wondering, first, just out of curiosity (yes, I am a physicist), and second, because 2.5 kilojoules left unaccounted-for are likely to get pretty hot.
I must confess, though, that my mental image of a 1 F capacitor is still about the size of a garbage can, and I am in fact overwowed by the existence of kilofarad capacitors.
A joule is a watt-second, so a kilojoule gives you a watt for a thousand seconds, or a thousand watts for a second, or any other combination such that watts times seconds equals a thousand. So 11 kJ could give you, say, 100W for 110 seconds - a bright car headlight on full beam for just under two minutes. In terms of total power storage, it’s unspectacular; even a small lithium battery can store several watt-hours. But a capacitor will stand far more abuse - if you need enormous current for a short time, a capacitor will do it, and it takes a fairly special lithium battery to charge in 16 minutes, never mind 16 seconds as quoted above.
The biggest thing is that batteries are a much more mature technology than capacitors, and we know how to improve capacitors more than we know how to improve batteries. You can make a battery store a little more energy by finding a slightly better chemical reaction, but we’re pretty close to the limit, there. With a capacitor, though, you can increase the storage capability by increasing the surface area of the electrodes, and there’s still plenty of room for improvement there. In other words, it’s not so much the current capacitors that can store about as much as a battery that are exciting (though they already have a number of applications, in certain niches): It’s the future capacitors, which will be able to store much, much more.
The one thing I worry about with capacitors, especially as energy storage in a car, is the result of catastrophic failure. It’s like a tightly wound spring, or a compressed air cylinder, the only thing keeping all that energy contained is the physical integrity of the unit. As you increase the area of the electrode, the physical barriers get thinner and thinner.
I can smash a lithium battery with a sledgehammer, and the stored energy just sits there in the chemicals.
There have been many, many reports of Lithium batteries bursting into flame, and even exploding, so i don’t think they are quite as safe as you believe.