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A scientific accident that could change the world

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Re: A scientific accident that could change the world

#91

Post by Someone »

sherjilozair wrote: post #24
buster wrote: post #19

Earlier quoted context omitted.

There is a big miscalculation: Graphene seems to be extremely light weight. 1 liter of graphene will definitely not weight 1kg. Wikipedia [1] only gives measures for m²: Graphene is very light, weighing only about 0.77 milligrams per square meter. [1] https://en.wikipedia.org/wiki/Graphene

Here[1], the density is said to be as low as 0.03 gm/cc which is the same as kg/liter. That gives a multiplicative factor of 33 over the above calculations, i.e. this could be 33% of the energy density of lithium ion batteries. Not bad. [1]: http://www.strem.com/uploads/resources/documents/graphene_na...

Energy per liter also is an important factor. Your mobile would float, but it also would be the size of your lower arm. Maybe, you should wear your battery as a jacket or a pair of trousers?

Re: A scientific accident that could change the world

#92

Post by mbell »

gallerytungsten wrote: post #79
mbell wrote: post #64

Earlier quoted context omitted.

True but you've got to consider the numbers we're looking at here. As an example an iPhone 5 has a 5.45Wh battery, if you wanted to replace that with a super-cap and charge it to 5V in 20 seconds you'd need to provide ~1000W of power or 200A @ 5V. Even if the super cap had very low ESR, call it 1mOhm, which is extremely low compared to current super-caps, you'd still end up dissipating 40W as heat with ~96% efficienc…

Perhaps phone makers can start making their cases out of aluminum, with enough mass to take the heat. 40W over 20 seconds doesn't sound too daunting. If you split such an aluminum backplate into two parts you could use them as the power contacts. Then you could have a "coffin" type charger where you put in the phone, then closed a cover to run the charge cycle. Kind of like the cover of a washing machine, to reduce t…

> 40W over 20 seconds doesn't sound too daunting.

It would be 40W _for_ 20 seconds, or 800 Joules, which is a lot of heat, enough to boil 3 grams of water that started at 20C or increase the temperature of 30g of aluminum by ~30C over ambient.

Re: A scientific accident that could change the world

#94

Post by bluedanieru »

dj-doppelganger wrote: post #75

Hi - 1st post on Haker news. Please be nice :) Aren't debates over energy density of super conductors v. Li-Ion batteries missing the important point, relative cost? E.g. If the energy density is 1/4 lower but the cost is 1/40th as much then electric cars get ALOT more viable. Can anyone guess at the relative cost?

How important that point is depends on how much range affects viability as opposed to the cost of the vehicle itself. Electric cars are rather expensive I guess, but few people are going to make the switch to cheaper cars if they only have a range of 20km.

Re: A scientific accident that could change the world

#95

Post by MichaelApproved »

AndrewDucker wrote: post #72
Selfcommit wrote: post #68

Earlier quoted context omitted.

Yeah, I don't understand the down votes honestly. We've seen this - not just a few months ago. Why is it ok to post again? Should I have provided the HN link?

It's more that your comment didn't add anything to the conversation. If you'd said "You can find the previous conversation at XXX" then you'd be contributing. As it is you just added noise.

Thanks for elaborating for me. The key point is adding to the conversation. Novelty accounts tend to be the realm of Reddit but one of my favorites is the one that says "Anyone looking for more information..." and goes on to list past posts of a link. That's infinitely better than simply "Repost"

Re: A scientific accident that could change the world

#96

Post by ChuckMcM »

BenoitEssiambre wrote: post #4

Conspicuously missing is any mention of energy density. Who cares about power density. That's juste how fast it can discharge. We don't need capacitors that can discharge faster. All capacitors are already much better than batteries with respect to power. We need capacitors that can store more energy. Capacitors typically suck at that and this article doesn't give any indication that these new ones are better.

Excuse me? This from the linked article (and in the paper abstract):

"These micro-supercapacitors demonstrate a power density of ~200 W cm−3, which is among the highest values achieved for any supercapacitor."

Granted its not a legitimate energy density (wrong units) but lets guess it is 200 Ws per cubic centimeter. I make that guess based on the comment in the video that they ran an LED for 5 minutes. So an LED is like 15mA and with a forward drop of a couple of volts so 30 mW. For 5 minutes your looking at 9000 mW-seconds, or 9 Ws for the small capacitor they showed in their video which could have been about a cm ^ 2. So if the cell they had made was 1/2 mm thick then a stack of 20 of them would be 1 cm^3 and 180 W-seconds (in the ball park of the abstract). There is a fun presentation on Supercaps [1] that was given to DoE in 2011. This computation does suggest that 200 Ws for this material would be a decent jump in capacity.

That said, I immediately dug an old LightScribe CD recorder out of my junk bin to start playing around with making graphene sheets :-)

[1] http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_revi...

Re: A scientific accident that could change the world

#97

Post by Retric »

sliverstorm wrote: post #65
mapt wrote: post #51

Earlier quoted context omitted.

A square meter of a single-atom-thick layer of graphene isn't very relevant. Expect the final product to have a volumetric density in the neighborhood of graphite or diamond.

Probably closer to graphite, as to my knowledge graphite is literally just layers of graphene.

You need to separate each layer with an insulator to be effective, otherwise you could just use graphite.

Re: A scientific accident that could change the world

#98

Post by AnthonyMouse »

mbell wrote: post #64
ScottBurson wrote: post #62

Earlier quoted context omitted.

Charging capacitors is normally much more than 90% efficient. They're not like batteries, where a chemical reaction occurs during charging. Resistive losses in capacitors are normally negligible. In this case they will probably still be negligible, I'd guess, because of the high conductivity of graphene.

True but you've got to consider the numbers we're looking at here. As an example an iPhone 5 has a 5.45Wh battery, if you wanted to replace that with a super-cap and charge it to 5V in 20 seconds you'd need to provide ~1000W of power or 200A @ 5V. Even if the super cap had very low ESR, call it 1mOhm, which is extremely low compared to current super-caps, you'd still end up dissipating 40W as heat with ~96% efficienc…

>200A @ 5V

I don't think so. Have a look at the comparison image around 3/4ths of the way down the page here:

http://www.interfacebus.com/Copper_Wire_AWG_SIze.html

14AWG (the small one) is the one rated for 20A which you might find in the power cord for a desktop PC, and is significantly bigger than the wire on your current phone charger. The big one (1/0) is rated for 125 amps. You have to go to 3/0, two sizes higher than that, for 200 amps. 3/0 gauge wire is what they commonly use for the main electrical service for a commercial building.

There is no way they would use a 5V charger if it had to draw that much current. But then you have a different problem: High voltage DC is extremely dangerous because it causes your muscles to contract if you come into contact with it, so your heart stops and you can't move to separate yourself from the electrical source.

20 seconds for a full charge is just unrealistic. Make it 60 seconds, and use a 24V charger, and now you're well within reason.

Re: A scientific accident that could change the world

#99

Post by herdrick »

gus_massa wrote: post #37
alexjeffrey wrote: post #3

I'd love to see this technology being incorporated into Tesla's batteries. With super-fast and long lasting charges their cars might become viable in countries where charging stations are either incredibly rare or nonexistent.

I searched a little, but the information is confusing. The superchargers (apparently) use 90kW/480V=~190A. I want to highlight this: 190A!!! A usual home connection can handle only up to ~10A, so 190A is a lot of current. To handle this you must use very thick wires. To charge faster you need move voltage or handle more current, probably you will need even thicker wires and to be careful with the safety measures. Add…

I think there's little issue with heat, as a major advantage of capacitors is efficiency in charging and discharging.

Re: A scientific accident that could change the world

#100

Post by wamatt »

ChuckMcM wrote: post #96
BenoitEssiambre wrote: post #4

Conspicuously missing is any mention of energy density. Who cares about power density. That's juste how fast it can discharge. We don't need capacitors that can discharge faster. All capacitors are already much better than batteries with respect to power. We need capacitors that can store more energy. Capacitors typically suck at that and this article doesn't give any indication that these new ones are better.

Excuse me? This from the linked article (and in the paper abstract): "These micro-supercapacitors demonstrate a power density of ~200 W cm−3, which is among the highest values achieved for any supercapacitor." Granted its not a legitimate energy density (wrong units) but lets guess it is 200 Ws per cubic centimeter. I make that guess based on the comment in the video that they ran an LED for 5 minutes. So an LED is l…

>That said, I immediately dug an old LightScribe CD recorder out of my junk bin to start playing around with making graphene sheets :-)

You serious? Sounds interesting, do tell us more.

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