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Super battery -> super capactor

  1. Jun 10, 2008 #1

    taylaron

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    super battery --> super capactor

    Hey, we all know battery technology is down in the dumps right now; and is keeping electric cars off the road.
    I've done some research on super capacitors but all the ones I've seen are based on a collection of several dozens of smaller capacitors.
    I've been thinking about the whole concept behind a capacitor which to my understanding is to store a charge on the surface of a material which is next to a parallel object where it can discharge when it has reached its peak charge upon the adjacent plate.
    Surface area, right! More surface area, more charge right? Well how do you get maximum surface area?
    if you look way into a cell in your body you'll find mitochondrion's which are objects with a massive amount of walls folding in on itself in order to create maximum surface area to generate maximum ribosomes. I think the following idea is similar:

    I do admit that there are a number of stumbling block to my plan but it its this:

    this super capacitor consists instead of metal which is usually the substance to hold the charge on; but I propose growing an inconceivable amount of carbon nanotubes, where you would chop them up into as many pieces as possible (as to further increase surface area from the ends) and store a charge upon the surface of these tubes. As a collection, the combined charge should be immensely more than that of today’s super capacitors; right?.
    I find this process similar to the mitochondrion. Carbon nanotubes are very small and what is the better choice to store a charge on than a massive amount of something very small in size; which has lots of surface area for its size. You would have a chamber of x size where it would be compacted with as many carbon nanotubes as possible. this would form the inside of a cylinder shaped object where all the surrounding walls inside the chamber (outside of the clump of nanotubes) would be an insulator of some sort then another conductive material that has no charge upon it.
    This is the same concept behind a regular capacitor right? You’re storing charge on the surface of small nanotubes inside a container with 2 walls; 1 is an insulator and 2, the metal plate.

    There is a way to manufacture a capacitor where it can discharge itself at whatever rate a charge is being drawn from it (like a battery but with no flow limit) or can you do this with some capacitors today?

    There is great problem in the growth of such a huge amount of carbon nanotubes efficiently; which I’ve find has never been successfully done at this scale (according to my research). any ideas on how to solve this?

    I need some input from some electrical engineers as well as physicists as to see if this would work and or how it can be perfected.

    -just trying to solve the battery crisis.

    -I would appreciate it if you could give some help that a high school student would understand. Thanks. I appreciate your help.
     
  2. jcsd
  3. Jun 10, 2008 #2

    mgb_phys

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    The tricky bit would be making a connection to each of the nanotubes anda separate connection to each of the inside electrodes while not allowing any of the inner electrodes to short to the tubes.
    It is an area that is being looked at, possibly with some electrolyte liquid involed so it is more like a battery with enourmous surface area.
     
  4. Jun 10, 2008 #3

    taylaron

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    wouldn't the liquid inside the chamber with the CNT's kind of defeat the purpose?
    -eliminating the surface area (from my point of view)

    why would you need to make a connection with each and every CNT?
    i suggest filling a chamber full of sand (representing the CNT's) and lining it with an insulator and a conductive layer outside that.
    i realize that these are carbon nano tubes not cylinders. so there is the outside surface area and the inside area. the charge would be stored on the outside correct?
     
    Last edited: Jun 10, 2008
  5. Jun 10, 2008 #4

    mgb_phys

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    The charge is stored on each of the two plates/conductors, the energy is stored on the field between them, picturethem as lots of little bits of TV coax cable.

    To get lots of energy in a capacitor you need either.
    1, Very high voltages, but there isobviously a limit before the material between the plates breaks down.

    2, A large surface area, butit has to be a surface area with a field between it. You can't have a large bucket of positive nano tubes and a distant bucket of negative ones and count thoseas large areas.

    3, A high dielectric. Putting a special insulating material between the plates allows the same field to store more energy than if they were simply spaced in vacuum. It is finding material that can store very large fields (have large dielectric constants) that is the drive behind supercapacitors.
     
  6. Jun 11, 2008 #5

    taylaron

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    perhaps im thinking of something along the lines of a battery. as i hear more and more; this idea doesn't sound very much like a capacitor at all.
    i was under the impression that if you could build up enough charge -like that of a chemical battery; and you could drain as much energy as you wanted as fast as you wanted. (unlike a chemical battery)
    i don't understand the need for another plate in this (sounds out of the question i know) i realize that there has to be a negative terminal for the entering electrons to be stored. would the other plate be for the negative terminal? if so; then only half of the charge on the positive terminal could be used because the potential difference between the terminals would eventually reach zero. would this slow down the power consumption?

    i suppose im confused now; is this a battery or a huge capacitor?
    -thanks for your patience.
     
  7. Jun 11, 2008 #6

    LURCH

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    Along the lines of increasing surface area, that is the idea behind this invention:
    http://web.mit.edu/erc/spotlights/ultracapacitor.html

    The creator, Professor Joel Schindall, also noticed the similarity between the way this cap stores charge and the way it is stroed by batteries. He has even started calling it the "synthetic battery." If he can get the cell chemistry figured out, EV's could become a viable technology.
     
  8. Jun 11, 2008 #7

    mgb_phys

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    Thats the work I was thinking of. I suppose at some point a capacitor where there is a chemical change in the dieltrci and a battery overlap.
     
  9. Jun 11, 2008 #8

    taylaron

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    well then,
    sounds like our friends over at MIT have already solved the problem then.....practically...
     
  10. Jun 13, 2008 #9

    LURCH

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    Yeah, "practicaly." When I first read that website in '05, I was pretty excited about the statement that they would have a working prototype "in a few months." I e-mailed Dr Schindall about 3 weeks ago (3 years after the article), and he said they are still "just a few months away" from a working prototype.

    Perhaps the rising price of petrol has increased the "gravity of the situation" to the point where time-dilation has become significant?
     
  11. Jun 17, 2008 #10
    Honda have already created ultracapacitors to augment the main power supply (in there fuel cell cars, could easly be done for an EV or hybrid) (for peak burst accelerations) these ultracapacitors get charged up during braking:

    http://world.honda.com/FuelCell/FCX/ultracapacitor/
     
  12. Jun 17, 2008 #11

    mgb_phys

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    But in the hybrid it only stores power for a brief time, and is just used to reduce wear and tear on the battery from rapid charging. The trick is to make a supercap that can store a charge for a similair length of time as abattery.
     
  13. Jun 18, 2008 #12
    @mgb_phys

    I hear what you saying, however at present the storage capacity is about 10-15% of a li-ion battery, of course research in being done to improve it. But thats a long way to go.

    But in this setup it does actually work as described, it can charge up using degenarative braking, which a normal battery can't do{rapid charging}. Then during acceleration (or peak burts) you switch to the ultracaps, and then rapidly switch back to the normal batteries to provide the steady load.

    Think about it for a moment, batteries are great for medium currrent for a long time, and ultrcapacitors are great for high currents for short periods, batteries takes a long time to charge, capacitors a very short time. A mixed use of constant speed with acceleration is perfect for this combination of technologies.

    This method does increase range, and like you said reduces battery stress, li-ions do have a shortish lifespan (I think its around 10 years) and they are deadly expensive, for EVs li-ion packs can cost around £10,000-£20,000 thats a significant cost of the car!
     
  14. Jun 18, 2008 #13

    LURCH

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    As stated in the previous post, I think the real trick would be to make the cap store as much charge as the battery. That is what Professor Schindall at MIT is working on. As far as long-term storage is concerned, it is true that capacitors leak. However, large capacitors leak so slowly that I still think it would prefer them over batteries as a storage medium, if I had to choose between the two (provided, of course, that they stored in equal amounts of charge).
     
  15. Jun 18, 2008 #14

    mgb_phys

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    Yep thats what everyone is working on! And if you could store the same energy as in a battery then a cap is almost preferable to a battery (at least for high power applications).
    The issue with currently available supercaps (apart from the energy density) is their high leakage rate, so they are suitable for smoothing out power fluctuations as I said but you can't use them as battery replacements in things like UPSs or even laptops.
    I don't know the specifics of the MIT design - but it isn't available as a product yet.
     
  16. Jun 18, 2008 #15

    jambaugh

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    I think this bears repeating!
    I've gone round and round with a couple of people who thought they could build super-duper power storage just by arbitrarily increasing surface area. It is critical to understand that the energy is stored in the volume between plates and not at the surface.

    Ultimately this is true also for caps with dielectrics, electrolytic capacitors/super-caps and chemical batteries...(and even elastic materials such as rubber bands and chemical energy once you get right down to it.)

    So if one wants to think up a better electronic energy storage device one must increase the extent to which one can control (change) electrical field strength per unit volume.
     
  17. Jun 18, 2008 #16

    mgb_phys

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    I thought you were going to object that the energy isn't the field but the rotation of dipoles in the dieletric.
     
  18. Jun 20, 2008 #17

    jambaugh

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    Why would you think I'd say that?
     
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