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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
Philip Jose Farmer predicted "batacitors" in his novels decades ago. Chalk annother one up for life imitating science fiction.
Good point. Maybe the nanotubes actually mesh between each other - kind of like the teeth in gears. Can't see it being easy to manufacture, but that would definitely provide a massive increase in closest-point surface area.
Meta will eat itself
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
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.
I believe that the height of the carpet of the nanotubes on the electrodes is going to be small relative to the thickness of the dielectric material between the electrodes. That dielectric thickness is the limiting factor for typical capacitors. The dielectric can only be so thin before it can no longer prevent current flow, maintain mechanical integrity, etc. Otherwise, you could store unlimited energy in a capacitor by making the dielectric thinner and thinner. With these, the dielectric thickness can stay the same, but the surface area on each electrode can be much higher. That is like making a physically bigger capacitor.
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.
The nanotubes are there to tremendously increase the surface of one electrode. All electrolytic capacitors I know use some sort of oxide as dielectric, and I presume the oxide would cover the whole nanotube. The other electrode is constituted by the solid/liquid electrolyte that the nanotubes are immersed in, surrounding them from all directions and utilizing the exceptional surface increase.
So the nanotubes from one electrode are not immersed in dielectric (insulator), they are immersed in the other electrode.
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.
In electrolytic capacitors, one electrode is formed by a conducting liquid, and an oxide layer on the metallic conductor acts as the insulator. The nanotube version may use something like this.
On another note, every time someone proposes to replace batteries with capacitors, I wonder how they make up for the huge variation of voltage that a capacitor delivers. Basically, the voltage of a capacitor is proportional to the amount of charge stored, whereas a battery provides more or less constant voltage. The capacitor-battery would require a circuit (something like a switching power supply) to be able to provide constant voltage. That, in turn, would take up space and waste some energy.
Escher was the first MC and Giger invented the HR department.
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.
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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.
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).
There are some very efficient (90%+) DC/DC converters available right now. Some will even automatically switch from step-up to step-down mode on-the-fly. Many battery powered devices already use these ICs to supply the multiple voltages needed, e.g. 1.5V and 3.3V logic, and 10-14V for a white LED backlight in phones and digital cameras So designing these devices to use a nanotube capacitor wouldn't necessarily require a more complex or less efficient power supply. So I think we can solve the voltage issue if they can build the capacitors.
I am not a crackpot.
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.