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which will win capacitors or batteries?

Discussion in 'Electronic Design' started by Jamie M, Nov 25, 2011.

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  1. Jamie M

    Jamie M Guest

    Hi,

    Assuming both technologies hit their limits at the nano-scale which
    will store more energy per volume/mass and which will have more power
    per volume/mass? I think capacitors have the advantage that the
    structure is fixed, ie. only electron charge is moving, whereas for
    batteries ions are moving which can wreck the structure of the battery
    over time, but can capacitors surpass batteries at the nano-scale?

    cheers,
    Jamie
     
  2. Guest

    Other than the buzz-word of the decade, what exactly does "nano-scale" mean?

    Capacitors store energy by keeping charge carriers separate. Batteries store
    energy in chemical bonds. Batteries win - no comparison.
     
  3. Les Cargill

    Les Cargill Guest


    So what ever happened to Pam Dawber?
     
  4. Both are equivalent. Both store electrons in the valence shell of atoms. In
    cause the potential is created by the macroscopic separation of atoms while
    in the second is is microscopic(on the atomic scale). You could image the
    chemical bonds as a sort of capacitor. The difference is that in the case of
    a capacitor a large number of electrons can be "stored"(there is actually no
    storage of electrons but just a displacement which is why capacitors block
    DC) quickly released due to the mobility of the carriers. This is more
    difficult in chemical reactions. Chemical reactions generally can hold
    higher energy densities(think of TNT) due to the shear number of atoms
    used(compared to the number of electrons on your standard cap)

    Ultimately one would expect the two phenomena to merge since they are based
    on the same fundamental physical principles(one of electron mobility). You
    can already see the phenomena overlap with plate capacitors and solidstate
    batteries or electrolytic capacitors and dry cell batteries.

    Capacitors generally depend greatly on the material configuration but a
    counter example are tantalum caps.
     
  5. John S

    John S Guest

  6. "John Larkin" wrote in message
    Well, lets see, one electron has a mass of about 10^-31. Therefor there are
    about 0.5*10^31 electrons in your "pound". There are 29 electrons in a
    copper atom so this equates to 0.5*10^31/29 copper atoms. A copper atom has
    a mass of 63*1.6*10^-27 kg so 0.5*63/29*10^4 ~= 10^4 kg.

    So besides the fact that your "pound" of electrons would require a huge
    amount of copper we are not even considering the fact that only the valence
    electrons would play any part in conductivity.

    If your wondering why I went through this mess it is to get you to realize
    that a "pound" of *free* electrons would be quite useless much less a pound
    of bound electrons.

    Maybe someone will figure out how to confine a "pound" of free electrons in
    a small space using a magnetic field but it would take quite a force to keep
    them together... probably more energy than man has ever or will ever create.

    The fact is that electrical conduction is a chemical process. The difference
    between the two is the type of chemical bonds in play.
     
  7. Jamie M

    Jamie M Guest

    Hi,

    I think "limits at the nano-scale" could mean that the technology would
    run out of atoms to create more surface area ie. for a capacitors
    "plates" or basically structuring the matter as much as possible down
    to the atomic/molecular scale. I guess it would be better to state that
    instead of saying nano-scale..

    cheers,
    Jamie
     
  8. Jamie M

    Jamie M Guest

    Hi,

    Capacitors don't break/form any chemical bonds, so aren't equivalent to
    batteries.

    cheers,
    Jamie
     
  9. "Jamie M" wrote in message news:jaq0sl$3ii$...
    How do you think electrons move around in a conductor? Do you think the
    electrons in a capacitor are free? That is, they are not bound to atoms? If
    they are bound to atoms what is the bond?

    --
     
  10. Jamie M

    Jamie M Guest

    Hi,

    There is no flow of matter in a capacitor between the electrodes, in a
    battery there is.

    cheers,
    Jamie
     
  11. "Jamie M" wrote in message news:jaq6om$g49$...
    Did you just avoid the question I asked?

    I suppose you think electrons are not "matter"?

    I think what you mean, given your lack of intellect, is that there is no
    flow of atoms or molecules. In a battery the electrolyte functions to prove
    easy mobility for electron migration but it is no less the same fundamental
    principles at work.

    So here's your argument:

    1. Electrons in a capacitors don't form chemical bonds
    2. There is no "flow" of "matter" in a capacitor

    Is this correct?

    Maybe when you realize that electrons form bonds with atoms you might start
    to figure out why capacitors and batteries are different. It has nothing to
    do with the erroneous things you believe but the strength of the bonds used.
    In the case of a capacitor the chemical bonds are very weak and electrons
    can easily migrate from atom to atom and extra electrons can be forced in
    the atomic lattice(go read up on valence band theory). For batteries, The
    chemical bonds are much stronger and require a chemical reaction to break
    the electrons free. This necessitates the mobility of the atoms as now they
    are required to move(since the electrons are stuck to them, unlike
    conductors).

    The whole point is that electrons have to move to prove the current. The
    principles at work are fundamentally the same but function differently due
    to the different materials used(and in some cases there is some overlap).
    I'm sorry you can't understand it. You should have paid attention phys 101b.
    --
     
  12. Nico Coesel

    Nico Coesel Guest

    No. A battery has a more or less constant voltage which means you can
    use the full capacity. A capacitor adheres to E=0.5F * V^2 which means
    that the voltage has a direct relation with the energy stored. This
    makes it very hard to charge and discharge a capacitor efficiently.
     
  13. Ralph Barone

    Ralph Barone Guest

    At most 1/1862 of a pound of electrons...
     
  14. "John Larkin" wrote in message
    First, that isn't what he said. He said they do not break or form chemical
    bonds. This is patently false, at least if you believe in modern day
    physics. He also implied earlier that a capacitor contains free electrons...
    again, false.

    Second, no one mentioned anything about changing chemical composition.
    Obviously the whole reason why batteries work is because one changes the
    chemical composition.

    As I said in the an earlier post, it all has to do with the strength of the
    bonds. That alone should tell anyone with any basic knowledge of
    chemistry/physics that there is a difference.

    Conductors have a high electron mobility which allows massive amounts of
    electrons to flow quickly. This is why capacitors can be charged and
    discharged quickly. Electrons in an atom that is "conductive" has very weak
    bonds and can easily be removed or added(depending on specific type of
    atom).

    In batteries the atoms carry the charge and electron mobility only occurs at
    the electrodes. As the chemical reaction takes place the electrons migrate
    through the electrolyte to cathode then through a conductive path and to the
    anode of the battery. The migration of atoms are much slower as they are
    much larger and must travel much larger distances than your typical electron
    in a capacitor. (It's more complicated than this because the electrolytic
    solution is full of recombination's)

    The goal then is to quick charge and discharge rates like a capacitor and
    high capacity like a battery. Since you physically cannot put enough
    electrons on a cap of any practical size to contain as much energy as a
    standard battery(See the other post about a "pound" of electrons) the
    approach would be to reduce the distances having to be traveled by the atoms
    in a battery.

    The nanoscale approach is effectively reducing the anode to cathode distance
    which increases the charge and discharge rates. We achieve the same thing on
    the macroscopic scale when we put batteries in series and parallel. If we
    can shrink this down to the nanoscale then use charge/discharge rates could
    be realized. The problem with this, just like with capacitors, that the
    capacity decreases.

    If we can design a device that uses the conductivity of capacitors and the
    capacity of electrolytes then we might get somewhere. e.g., have a
    conductive channel, on the nanoscale, that can transport the electrons
    quickly instead of having to transport them through ion mobility(which is
    much much slower than electron mobility in an electrolyte). In some sense we
    allow the electrons to "hitch a ride" on the conductor. This maybe what is
    happening in some of the newer lithium ion designs that use nanowires.
     
  15. Guest

    With a net neutral charge. What's your point?
     
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