In reply to Michel Jullian's message of Mon, 29 Jan 2007 10:04:52 +0100: Hi, [snip] >Interesting, can you provide the exact formula, and what are the absolute >dielectric constant and the breakdown voltage strength (max V/m) for barium >titanate?
The exact formula is derived from the capacitance formulas for a flat plate capacitor, and the energy stored in a capacitor. The energy density works out to 1/2 x epsilon x (breakdown voltage/unit distance)^2. (This assumes that the absolute breakdown voltage is linear with thickness, which is the best case scenario according to http://www.wrightcap.com/ceramic-capacitors-material-spec.html . For Barium titanate I find figures of dielectric strength = 34 kV/cm and dielectric constant of 7200 @ http://www.ingentaconnect.com/content/klu/jecr/2005/00000015/00000002/00001460 which yields an energy density of 368 J/L. The EEStor crowd claim to have material with a dielectric constant of 18000 (according to recent news IIRC), and from the patent: "These coating materials have exceptional high voltage breakdown and when coated onto the above material will increase the breakdown voltage of ceramics comprised of the coated particles from 3.times.10.sup.6 V/cm of the uncoated basis material to around 5.times.10.sup.6 V/cm or higher." So for the uncoated basis material they claim 3E6 V/cm (about 100 times higher than from the other report here above - if I read correctly ?!? - I suspect this should be 3E6 V/m). Thus we get two different energy densities, depending on whether or not there is a typo. 1) 7.17 MJ/L 2) 717 J/L Somehow, I suspect the latter is more likely to be correct. BTW they actually claim a breakdown strength of "5E6 V/cm", for their composite design, so once again assuming this should be 5E6 V/m we would get a purported energy density of 1992 J/L, or 19.92 MJ/L if the voltage claim is correct. BTW I seem to remember them claiming 52 kWh for a 100 lb device. If we assume a density of 2.7 gm/mL (about average for ceramics) then this works out to 11 MJ/L (not too far removed from (1) here above), so it seems they have either discovered a substance with a breakdown voltage strength a hundred times higher than air, or they have fallen victim to their own typo. BTW2 Try calculating the energy density of an electrolytic cap. for the fun of it. :) In short, I think I would be betting on the Li ion batteries. ;) >Indeed atmospheric ingress can be an important factor, since the material >seems to be a porous ceramic. The size of the pores, and the nature of the gas >filling the pores could well be what determines the max V/m! > >Michel > >----- Original Message ----- >From: "Robin van Spaandonk" <[EMAIL PROTECTED]> >To: <vortex-l@eskimo.com> >Sent: Saturday, January 27, 2007 11:35 PM >Subject: Re: [Vo]: More on the Bettery > > >> In reply to Michel Jullian's message of Sat, 27 Jan 2007 14:11:55 +0100: >> Hi, >> [snip] >>>Unless the coatings diminish the material's permeability to some atmospheric >>>gases lowering it's breakdown voltage? >>> >>>Michel >> >> I would think that insulation from the atmosphere would be more cheaply and >> easily obtained with a plastic sealant. >> BTW there is no real reason to operate at such high voltages. By making the >> dielectric material in the capacitor thinner, the capacitance per unit area >> is >> increased, and also the total number of plates in a given volume can be >> increased. Both of these together compensate for the drop in voltage, so in >> fact >> any desired operating voltage can be accommodated. It turns out that the >> maximum >> *energy density* of the device (J/m^3) is purely a function of the material >> used >> as dielectric in the capacitor, and is proportional to the product of the >> absolute dielectric constant of the material and the square of breakdown >> voltage >> strength of the material (V/m)^2. >> >>> >>>----- Original Message ----- >>>From: "Robin van Spaandonk" <[EMAIL PROTECTED]> >>>To: <vortex-l@eskimo.com> >>>Sent: Tuesday, January 23, 2007 10:50 PM >>>Subject: Re: [Vo]: More on the Bettery >>> >>> >> [snip] >>>> The EEStor patent is US7033406 which I believe contains a design flaw. >>>> They state that the base material (Barium Titanate) is coated with Aluminum >>>> Oxide and Calcium Magnesium Aluminosilicate, which coatings are intended to >>>> increase the breakdown voltage of the composite. They then go on to >>>> calculate >>>> the energy density based upon this increased breakdown voltage. >>>> >>>> However IMO, what happens in reality is that a high voltage drop will occur >>>> across the high breakdown voltage component, and a lesser voltage drop >>>> across >>>> the Barium Titanate. IOW with such a composite construction, one can't >>>> simply >>>> apply the full voltage to the entire material for the purposes of >>>> calculating >>>> the energy density of the whole. The real energy density of any given >>>> material >>>> is actually a constant, and no "trick" of design is going to get around >>>> that. >>>> Since they specify that the breakdown voltage of Barium Titanate itself is >>>> only >>>> 60% of that of the other materials, and since voltage appears squared in >>>> the >>>> formula, the real energy density of the finished product is IMO going to be >>>> nearer 60%^2 = 36% of their claimed energy density, which would be about 3 >>>> times >>>> the energy density of lead-acid batteries. >>>> >>>> Regards, >>>> >>>> Robin van Spaandonk >> Regards, >> >> Robin van Spaandonk >> >> http://users.bigpond.net.au/rvanspaa/ >> >> Competition provides the motivation, >> Cooperation provides the means. >> Regards, Robin van Spaandonk http://users.bigpond.net.au/rvanspaa/ Competition provides the motivation, Cooperation provides the means.
