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Capacitors to Replace Batteries?
An anonymous reader writes "MIT's Joel Schindall plans to use old technology in a new way with nanotubes.
'We made the connection that perhaps we could take an old product, a capacitor, and use a new technology, nanotechnology, to make that old product in a new way.'
Capacitors contain energy as an electric field of charged particles created by two metal electrodes, and capacitors charge faster and last longer than normal batteries, but the problem is that storage capacity is proportional to the surface area of the battery's electrodes.
MIT researchers solved this by covering the electrodes with millions of nanotubes.
'It's better for the environment, because it allows the user to not worry about replacing his battery,' he says. 'It can be discharged and charged hundreds of thousands of times, essentially lasting longer than the life of the equipment with which it is associated.'"
I'm sick of that bloody rabbit. Now it's going to last forever. Perfect.
Meta will eat itself
I thought the charge was on the parts of the plates nearest each other, so the surface area would only be that of the ends of the nano-tubes. This would be smaller than if they had a flat plate!
Philip Jose Farmer predicted "batacitors" in his novels decades ago. Chalk annother one up for life imitating science fiction.
The fast charge has its obvious benefits, but I'm wondering about the durability of such nanotube filaments in the face of, say, the treatment your average laptop battery would have. Are these things resilient enough to be bashed around?
Are these capacitors only likely to be suitable for for small scale charges/discharges? Mobile phones? laptops? cars themselves?
More questions than insights, I'm afraid, but I find it fascinating
Thats just fantastic, sounds like the ideal replacment for batteries, and puts fuel cells out of business for small consumer products like laptops I'd have though, especially as they wouldn't cause any problems on planes.
hydrogen fuel cells would still be great for larger things like cars.
could these be produced in a way to fit in existing devices as soon as possible? I'f this really is safer for the environment, I'd love to see these asap, especially as most batteries are standard sizes already, even inside a laptop battery there are often (always?) muliple standard sized cells.
I hope they're easilly recyclable too, for when they do finally fail.
With its longer life and faster recharge time. I wonder if this could lead to an electric car that is good for the masses where they can cross country and take only 5 to 10 minutes to recharge. That is the primary reason why the Electric Car never made popularity it is because it is not convenient enough for normal people.
If something is so important that you feel the need to post it on the internet... It probably isn't that important.
You implied that a Slashdot comment author has a wife/girlfriend. Please don't. It only makes the inmates restless.
Summary says this technology would allow batteries to charge faster. It's a big understatement since the article says they would only need a few seconds to be fully charged...
First, safety. One of the amazingly cool things about capacitors is that they can deliver all their charge over the course of a few milliseconds. This makes them very useful for things like strobelights and subwoofers. But it can be very, very dangerous: What happens if you drop your in the toilet? Or you drop your iPod and it gets run over by a car? If they have batteries, a short circuit will cause the battery to get warm for a while, or it will release some slightly caustic goo and you have to wash your hands. But if they have capacitors, you get an explosion and a violent electrical arc.
Second, durability. You can beat the hell out of a chemical battery, expose it to shock and vibration to no end and it will continue to operate. These nanotubes, OTOH look awfully easy to break. Breakage could cause two things to happen: loss of capacitance, or worse, an internal short circuit, and see above.
It will be interesting to see how these two problems are addressed, or if these cool toys will be relegated to industrial and other controlled-environment applications.
This is not my sandwich.
From the looks of the detail sparce article I just made before I headed off to work (at a company that works with Nanotubes ironically enough), this actually looks pretty easy. The image of nanotubes that they show are almost certainly nanotubes made by chemical vapor deposition (CVD). CVD is cheap, scalable, fairly easy, and found in every semiconductor fab you have ever gone to. Now, I am not saying that there might be some real engineering challenges, but if alls they have to do is grow a mess of nanotubes ontop of a substrate as shown in the picture of the article, this is going to very easy and hit the market in the very near future.
That said, I would not hold my breath waiting for this product to come out. The making of the nanotubes in the way that they have is not hard, but I would be suprised to learn that there is not some other performance or quality issue that needs to be struggled with.
Capacitors also have another difference: they can be (dis)charged extremely quickly. That means you will be able to recharge very quickly (if you have a spiffy charger), but I wouldn't want to drop a capacitor powered cellphone in the toilet.....
10 ?"Hello World" life was simple then
I'd gladly pay 4 times (or more) the price of regular batteries to have batteries that recharge in seconds and never need replacing. This will be great in cell phones and laptops, too.
My experience with capacitors is limited but I do know that they are extremely dangerous. I do distinctly remember having to discharge the capacitors in my arcade monitor in order to replace some circuitry. This involved a screwdriver with a grounded chain soldered onto it, some rudder gloves, and some flinching like a little school girl when you hear that loud pop from the discharge. I'm not entirely certain I'd want this sort of thing powering my laptops and cell phones.
The capacitance isn't just a function of raw surface area. If that were the case, you could double the capacitance just by roughing up the surface of the capacitor plates. The contribution of any spot on the surface depends on the area of that spot and the distance between it and another oppositely charged surface as well as the dielectric constant of the material between the plates. You can increase the surface area as much as you want but you still have to get the surfaces to line up with each other.
It is hard to exceed a certain energy storage on a capacitor. As you move the plates together, the capacitance goes up and you can store more charge per volt. The breakdown voltage goes down as you move the plates together. So you can store a small charge at a high voltage or you can store a large charge at a low voltage. For a capacitor of a given volume, you can store only so much energy depending on the breakdown voltage of the dielectric material.
I don't doubt that you can double or triple the energy storage of capacitors compared with current technology. On the other hand, I am very skeptical about the possibility of getting enough capacitance to store enough energy to be a general purpose battery replacement.
I leave it to you as an exercise to calculate the capacitance of a 2 volt capacitor necessary to store one amp hour. ie. something similar to an AA battery cell.
You have never created an internal short circuit on a conventional (rechargable) battery, did you? It is also able to deliver all the stored energy on an explosion that will take your hand away.
Now, batteries don't explode all the time, because they are well blinded. Capacitors are less dangerous (carry less energy), so they are not that well blinded, and explode often. There is nothing stopping the people from making blinded capacitos out of economics, and it could be even safer than battteries, because there is no ion trading going on.
Rethinking email
If they have batteries, a short circuit will cause the battery to get warm for a while, or it will release some slightly caustic goo and you have to wash your hands.
:-/
Sorry, that's incorrect.
Try shorting a car battery with a screwdriver and tell me there isn't a violent electrical arc. Also, NiCads (and I believe NiMH) have very low internal resistance - if shorted, they can literally explode as they overheat dramatically. You're confusing this with non-rechargeable batteries, which behave as you describe.
Also, capacitors deliver charge at a rate dependent on the impedance of the load they're driving. It would be very straightforward to put a small resistor in the package containing the capacitor, so that the current out of it is limited.
Regarding the short-circuiting, capacitors require overlapping surfaces that are electrically insulated from each other. That means if you're using nanotubes, you'll want both sides covered in nanotube "fuzz" and the two sides then pushed together so that the two intertwine. This means that one (or preferably both) sides need their nanotubes coated with some kind of insulating material for it to work, otherwise the nanotubes will simply short out, and then you won't have a capacitor any more. And that means you won't get short circuits from random broken nanotubes in the structure.
Fragility I don't know about, but since carbon nanotubes are the strongest substance currently known, I suspect it's not going to be a huge problem. Also consider that the whole thing could easily be encapsulated in some solid insulating block so that it's a single physical chunk (remember that carbon isn't a metal so there are no significant expansion/contraction issues with heat). Batteries are only as solid as they are because they've got a solid metal case encapsulating well-packed electrodes and electrolyte - try dropping a plastic-case car battery from a height and tell us how solid it is.
Given how desperate battery manufacturers are for any kind of edge, I imagine this will be rushed to market as fast as physically possible!
Grab.
... And thus the comments about the mfg. process 'catching up'. I think we already don't use Li-Ion AA's and AAA's because they're cost-prohibitive, and the packaging is wasteful of space. I already wince at paying about US$2.50 per individual AAA for NiMH. But this technology promises features I think are worth paying for, just like having Li-Ion and Li-Polymer batteries in your cellphone, mp3 player, and PDA right now. Imagine when the battery for your cellphone or iPod is long-lived enough to be printed onto the circuit board and never replaced, and it can receive a charge in only a few seconds. If this is done properly, it'll eventually be the end of removable cells altogether.
This even opens up a lot of integration possibilities that just weren't there before, like peripherals that bring their own capacitor bank in to boost the system's capacity. Everything with a PCB can now cache its power, without all the bulk of a traditional battery. Imagine expansion cards that can carry the power needed for I/O (Wireless, Flash Memory, whatever) and charge with the system. You could even use the memory expansion slot as an auxiliary battery, like on some laptops how the optical drive can be replaced with another battery.
Take this with System-On-Package designs like were just recently discussed here, and we may get some really small electronics in our lifetime. You could even reduce capacity to save space -- I wouldn't mind charging my cellphone almost every night if it only took a few seconds.
True science means that when you re-evaluate the evidence, you re-evaluate your faith.
I used a 1989 vintage computerized stage lighting control console used a big capacitor soldered to the back of the PCB to hold the settings in RAM while the unit was switched off. Typically, the capacitor could hold a show for about three to four weeks and every time it was switched on, the capcitor would recharge. It still had a "modern" 720k floppy disk just in case.
This is a boring sig
The thing is, one kg of petrol holds around 45MJ of energy. One kg of NiMH batteries hold around 0.25MJ, a factor of almost 200 less. A lead-acid battery holds half that. A normal capacitor holds 0.002 MJ/kg.
So, even to compare with lead-acid batteries in energy-storage this thing needs to be 50 times better than normal capacitors.
Recharging in seconds is fine, assuming you can build a sensible car that goes oh say 100 miles at the least between recharges, that's perfectly acceptable for most people. Same for cellphones; faster recharging is very nice. But only if you can still go for 2-3 days without recharging, and talk on the phone for atleast an hour or two before its empty.
A car that could only go 20 miles between recharges would not be a hit, not even if the recharge was done in a minute.
A rustic farmer is sitting on his porch. In the distance a "toom toom toom" noise can be heard. A pissed off look crosses the farmer's face as he reaches for his shotgun. He opens the breach of the gun and inserts shells that look distinctly like Energizer batteries. As he looks out over his cornfield, a pair of white ears can be seen serenely sliding above one of the rows. He takes aim and then bolts of lightning lash out of the shotgun towards the stately sliding ears. Drumsticks, drumpieces, and exploded bits of Energizer bunny fly everywhere. A smoking pair of sunglasses lands right at the farmer's feet.
"I jes hate it when rabbits get in ma corn."
However, there is now a lot of academic and business interest in them as they are ideal for a wide range of modern applications. Devices like UPS's and power smoothers still run on lead acid batteries, which are bulky, contain corrosives and are prone to unexpected failure (at least mine seems to be). There is also a big push from the electric vehicle crowd. Note though that they are unlikely to form the primary power source for an electric vehicle (they still have poor energy density compared to chemical technologies), but are extremely attractive for both initial power-up (i.e. heating a fuel cell to running temperature) and for sensible implementation of regenerative braking - charge the supercap when you brake, use the energy for short term bursts (driving up a hill, overtaking etc).
At the very beginnings of electricity, it was stored in Leiden Jars, a form of capacitor. In the 1930's, the accumulator, a form of capacitor, was sometimes used to power early radios. Apparently, you used to carry these back to the shop to have them charged up.
The promise of replacing your computer battery with a capacitor that recharges in a few seconds probably can't happen all that time soon.
Some math to back this up: My work laptop, a Dell Latitude D610, has a 53 WHr battery. My home laptop, an Apple 12" Powerbook, has a 46 WHr battery. These aren't huge laptops, mind, and battery capacity is only on the rise as consumers demand more.
Let's use the Dell example, 53 WHr. Change hours to seconds, that's 53 * 3600 = 190,800 Watt-seconds (more usually known as Joules). 191 kJ - that's a fair bit of electrical energy to store, either in battery or in capacitor form. Let's ignore losses that occur in the charger and energy storage device - assume everything is 100% efficient for a moment.
What if we wanted to charge up that 191 kJ capacitor in, say, 10 seconds. That would require a 191 kJ / 10 s = 19.1 kW power supply. Hmmmm, don't think we'll be seeing one of those in a laptop bag anytime soon.
Laptop batteries are a particularly high-energy example, but it illustrates the kind of power increases you'd need to accommodate if instead of charging in hours, you charged in seconds. If you had a battery that used to charge in, say, one hour (cellphone, PDA, whatever), and you instead wanted to charge it in (again, for example) 10 seconds, the charging power supply would need to put out 360x more power. Even to charge it in a minute would require a 60-fold increase in power. That'd be an amazing and fascinating power electronics problem to consider - how to make such charging devices as compact as today's.
Imagine refulling your car by simply stopping at the traffic lights. A swipe system like the toll roads handles payment, and your off again. It would not be hard to have a recharge every 50 - 100km on the highway if they aren't manned. Just a drive though pitstop - and your back on your way.
Who cares if electric cars don't have huge range if recharge stations are everywhere. And if your a "but I like to spend 4 days driving in the wilderness", then you take extra storage... just like you do with petrol.
Oh,... and it would not be hard to fix the complaint about exploding capacitors... Seal them in plastic so there water tight. Only two wires in/out... A very small amount of circuitry would allow high current in for recharging, and have a current limiter on the way out. Not crush proof, but certainly water/short circuit/toddler proof.
100kW/kg is the power density, i.e. a measure of how fast it can output a particular amount of power per kilogram of device.
60Wh/kg is a measure of energy density, which is to say, joules per kilogram in a charged state - they are just using units of watt-hour, which can be more convenient for energy storage measurements.
To put it into a normalised form, we have
100,000 J/s*kg (joules per second per kilogram) for the power density,
and
216,000 J/kg (joules per kilogram) for the energy density.
So, one kilo of capacitor could dump about 216,000 joules of energy into something in slightly over two seconds.
I believe that also runs the other way around, with a two-second charge.
But IANAEE.