Friday, December 31, 2010

I believe Supercaps will win out over battery technology

Article: Graphene-based supercapacitor hits new energy storage high

John,

I'd like to know about longevity. Does it continue to store energy after 100 charges or 1000 charges? No mention made of that.


Caps don't have any degradation with charge discharge cycles like batteries.

They never wear out!

There are electrolytic caps that that are used in TV's and they dry out with heat, that's not usage related.  There life is depended on the oil used evaporating and not the capacitor itself.

But a graphene based supercap can charge almost instantly. can also discharge just as fast.

Caps typically can't hold a charge as long as a battery though.  So maybe a month or two sitting idle it would loose much of it's charge where a battery would still keep it.

From a theoretical side, of a cap was made from layer of superconductor and super dielectric, then it would have an almost unlimited storage capacity, limited only be the electrical breakdown of the materials.

When I was studying materials it was interesting to find that the best dielectrics had superconducting "zones" in them that would hold repelling charges.  I didn't quite understand it all, but it seemed that it was a similar problem to making superconductors.

So I suspect a cryogenic capacitor device if developed could hold massive power.


As I mentioned in my reply that was the electrolyte causing problems in just that one type of cap. There are many types of caps most will last for ever or to be more precise do not degrade from use.  Think of a radio circuit.  The caps charge and discharge million of times per second. 

The fundamental operation of a cap is two conductors with an insulator.   The charge is determined by distance and surface area.
Nothing deteriorates.
With electrolytic the insulator is the boundary between a coated metallic surface and the electrolyte that form a super thin insulated layer in only one polarity. Before. Nanotech it was the most efficient way. Is it still dirt cheap.  Paper and foil soaked in an oily electrolyte


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If there are super conductors, then are there are there super non-conductors?

Like a super dielectric?

Is this possible, what would it look like? Is cold better for dielectrics?

If this is possible then battery's are dead.

The capacitors energy storage goes up at the square of the voltage.
EEStor a vendor to GM for the volt came up with super caps that operate at 3600V while most super cap research was going for  thinner and lower voltage dielectrics.  The EEstor is the first supercap to be at 400 Watt hr per KG where Li-Ion batteries are at 200 and 1700 in the lab.

With a super dielectric we could do 1Million Volt caps that could store enough energy to power an electric vehicle for months with far higher power to weight ratios then hydrocarbons or batteries.

I had an idea to use computational chemistry to explore this, but maybe there is already something in the literature?

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Dear John,

"If there are super conductors, then [are there] super non-conductors?"--JS

   Heaviside calls a "conductor" an "obstructor". It obstructs the passage of electromagnetic energy. The superconductor has a zero propagation speed for electromagnetic waves. The degree of obstruction is the ratio of the speed of light in vacuum to its speed in the dielectric- the index of refraction. This is the source of the dielectric constant, which is simply another way of expressing the index (~lost knowledge, by the way).  So THE "super" dielectric is the vacuum, since the speed of light in vacuum cannot be exceeded.


"The capacitors energy storage goes up at the square of the voltage...
With a super dielectric we could do 1Million Volt caps that could store enough energy to power an electric vehicle for months with far higher power to weight ratios then hydrocarbons or batteries." --JS

Only if it also has a "super" dielectric breakdown strength. Resend-
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  It a common misconception that raising the voltage of a capacitor increases its energy storage density. This isn't true!

There are four major variables- the plate area, the gap , the dielectric constant ( a ~linear function of permittivity), and the dielectric breakdown strength, which is the maximum do-not-exceed electric field strength, in e.g. volts/meter,  for a given material.

Consider the equations for capacity and for energy stored-

(1) C = constant1*A/d  , where the constant1 is material permittivity, A is the plate area and d is plate gap, and for energy

(2) E = CV^2/2  (This is what makes increasing the voltage look very tempting.)

Substitute (1) into (2) to get

(3) E = constant2*A*V^2/d  (with the 2-factor absorbed into constant2)

Multiply through by A/A to get

(4) E = constant2* (AV)^2/Vol

 Assume that the volume of a capacitor made out of materials X and Y is proportional to its mass, i.e. constant density for any size, then

(5) Vol = A*d   (and mass = Vol* density)

Remember, to increase the voltage means that the gap, d, has to increase in linear proportion to maintain the same safety factor for a give dielectric breakdown strength.


> Only if it also has a "super" dielectric breakdown strength.

That's really what it's about a crystals (most likely) ability to resist conducting electricity and also have the mechanical strength to resist the mechanical forces to punch a hole through.

Vacuum doesn't make for a good HV capacitor.

JVP you'd appreciate this link, seems there is some geometric structures that make this material Super-K CCTO CaCu3Ti4O12 a very good dielectric, it has some interesting properties at low temperatures too.

The point of a super dielectric is to keep the gap distance as small as possible while increasing the voltage.
One article I found
http://www.azom.com/details.asp?ArticleID=898


John

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>It's a common misconception that raising the voltage of a capacitor increases its energy storage density. This isn't true!

>Remember, to increase the voltage means that the gap, d, has to increase in linear proportion to maintain the same safety factor for a give dielectric breakdown strength.

The problem is with manufacturing.  With ultra thin dielectrics the smallest imperfections will kill the device.  So building thick dielectrics are less affected by defects.

 It's the difference between clean rooms where a spec of dust will kill your device vs. something that can be made in a machine shop and full of dust and debris with no affect what so ever.

I'll never forget back in High School we made a Induction heater, the powersuppy was running at over 10KV and we made a massive bank of capacitors from sheets of glass and aluminum foil.  Point being is that had we used lower voltages and thinner dielectrics then the precision and defect tolerances would have dropped accordingly.

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