Supercapacitors are now carbon-free and more powerful | Hacker News Reader

Supercapacitors are now carbon-free and more powerful

edgylabs.com

78 pointsParbeyjr40 comments

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Classic modern reporting - doesn't link to the source or even cite the paper.

Here's the source: http://www.nature.com/nmat/journal/vaop/ncurrent/pdf/nmat476...

Web version: http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat47...

Not to mention: written by someone who doesn't haven't a clue about what they are writing about.

I quote:

> ... although conventional batteries have a slower recharging time, the fact that they maintain their charging capacity over a longer period because makes Li-ion the more efficient choice over carbon-based supercapacitors.

Nope. That's not it.

That description is so bad it makes me wonder whether the author even looked up capacitors on Wikipedia or if they just paraphrased what they think they remember from high school physics.

If I'm not mistaken the biggest disadvantage of supercapacitors is the energy density by mass[1], which means that while they hold a good power density by mass it's only temporary. Good at sprinting not so good at marathons.

It's great that there are advances in the field for many reasons, but I don't think they could replace batteries in the short-middle term, which seems to be the point of the "scientific click-bait" article.

[1] http://berc.berkeley.edu/storage-wars-batteries-vs-supercapa...

Regenerative breaking systems is one of the obvious places for supercapacitors. They are not quite at the energy density or cost level where every car uses them, but with some minor improvements they will become standard. The advantage is of course better mileage and increased battery lifespan.

PS: There are even advantages with IC engines: http://articles.sae.org/11845/

I didn't think about regenerative breaking and of course it looks like a good place. But in the end of the cannot this be absorbed by the batteries with a good configuration? I mean, adding N supercapacitors that can absorb X power each would be proportional as configuring it as M batteries (where M >> N) charging that can absorb Y power each where Y = X * N / M => Y << X, which seems doable. So you'd either need enough capacitors to use them effectively (adding cost/complexity) or enough batteries, right?

Is that the reason why Tesla can do regenerative braking except for strong stops? Because the batteries can absorb part but not all of the sudden energy?

I imagine the strong stop problem is more about actually stopping the car fast enough. Easier to do with friction than induction.

That will depend on your speed. High speeds favor inductive braking.

Anyway, if I were to guess, I'd say it's because ABS tech is very mature, and inductive breaking is not, thus safety favoring friction.

Battery's don't really like very short partial charge cycles, and the electronics to track these energy spikes get's difficult. Storing ~e6 J in ~5 seconds takes a lot of battery's. Also of note, because battery systems can only take X energy the rest of the system is only disguised to supply X energy. Most hybrids use battery's and simply kick in normal breaks if you do more than a slow stop.

But, with super cap's a lot of this goes away. They can store more energy so you can add larger alternators and recover more energy. Further, they have a higher % efficiency for charge / discharge cycles.

So, you have 3 tiers of rate vs capacity?

* Capacitor - high charge / discharge rate (power), low capacity (total energy). (and high risk of electrocution and spot welding)

* Battery - medium power, medium capacity.

* Small ICE - low power, high capacity.

The density/weight needs to be improved a lot for it to be effective compared to existing battery technologies though:

Mazda supercapacitor:

0.007kWh @ 6kg - 857kg/kWh

Prius with nickel-metal hydride batteries:

1.3kWh @ 42kg - 32kg/kWh

Tesla with lithium-ion batteries:

85kWh @ 544 kg - 6.4kg/kWh

Breaking systems only really need to contain enough energy to stop a car. So, up to 1/2 * 2,000kg * (40m/s)^2 = 1.6e6 J which is a lot of energy, though less than 3.6e+6 J. Going down a mountain is an important edge case, but frankly not something that you really need to use super caps for as these systems still have mechanical breaks for backup, and the lower peaks is more acceptable for battery's.

In an electric car you would then use that energy to speed up again, thus allowing for 10s if not hundreds of charge cycles on a single trip.

Note: 2000kg ~= 4,400lb, 40m/s ~= 90mph.

You forgot to divide by two.

It's actually 1.6 MJ, not 3.2 MJ.

Just edited before seeing your note. But, thanks I always forget about that 1/2.

Just to be pedantic, it is "brakes" for slowing things down, and "breaks" for ruining or damaging something.

Are these figures right ? Gasoline lists on wikipedia [1] as 46.4 MJ/kg which Google gets as 77g/kWh.

[1] https://en.wikipedia.org/wiki/Energy_density

Those figures are right, the best batteries today are still like one percent as good as gasoline at storing energy. Although, you can only get about 20 percent of the energy out of gas while you can get about 90 percent out of a battery.

Right, and ultimately, hydrogen is one of the most (if not THE most) efficient energy storage methods. However, as far a physical storage, actually putting it in a tank, it is not as efficient. Plus, burning it is not as efficient as electricity either.

Electricity and batteries are the way to go. They are around 90% efficient today and will only get better with better cooling methods and recapturing heat loss/preventing heat.

Carbon-free implies that there is zero carbon in this technology. In fact, the MOF material is based on organic (carbon-bearing) molecules.

"non-carbon-based" would be more apt, since this is definitely a change from carbon-based electrodes.

I agree the current phrasing is at best easy to misunderstand at worst misleading. Another phrase like mchannon is suggesting or perhaps "No longer uses just carbon" would be more acceptable.

MOFs are one of the coolest nanomaterials. They are easy to customize and are sort of like molecular tinker toys. One can make a new MOF with the same structure by exchanging one of the molecular struts for another. In addition they self assemble and can be made by the ton. I don't think we can make carbon nanotubes by the ton.

Chris Wilmer, a well known MOF researcher and bitcoin proponent, has an interesting talk on MOFs: https://www.youtube.com/watch?v=n1hcF2kYlC0

That is good news. How long time would it take this research to result in improved batteries being marketed for electric vehicles?

Maybe a year, maybe twenty. The tragic of research is that you have no idea before, so many great results never make it to market or far later than expected. But some day .. hopefully ..

this is one of a hundred such new battery technology we have been reading for the last 15 years. Batteries still have not changed in any great leap yet.

I don't know if that's true but save for electric vehicles, has there been any major interest in improving batteries much beyond what they do?

Batteries have been mass marketed for laptops and cellphones in the past couple of decades and have improved steadily for the increasing needs in those markets. It's okay for cell phones to last for a day and to charge in an hour. But with electric cars, which are only really starting to pick up in the last 2-3 years or so, demand for longer range and faster charging is quite different.

https://blogs.scientificamerican.com/the-curious-wavefunctio...

Charging speed is almost irrelevant for EVs. In the end you're limited by the amount of power you can push through a liquid cooled charging cable, and traditional batteries can almost certainly be engineered to handle that current.

Once you get to that level, further improvements will not be that interesting. Maybe we'll never reach ICE refueling speed. But with electric you can put a charging spot on every parking space in supermarkets etc, and people can just leave the car charging while they shop.

Energy density is the only thing that matters.

Good super capacitors have other great usecases though. But maybe not as sexy.

This may be true at first glance, but if you try to incorporate more advanced EV features, and in particular, regenerative braking, you very quickly do need to care about maximum charge/discharge rates. Your brakes dissipate a great deal of energy very quickly; to resorb that back into usable potential is something that supercaps are exceptionally good at facilitating.

That being said, in this case, you're likely best off using a supercap buffer between your batteries and the wheels, but that makes your power management and delivery systems substantially more complicated.

Could this be used to charge your car's supercaps in 30s and have them feed into the batteries over a longer period of time?

I think charging cables would melt from such currents. Or you would need a superconductor charging cables for your supercapacitors. Super everything :)

Thicker cables? Or would they be too heavy?

There will be a physical limit when you attach the cables to the capacitor. At some point, the cable will be larger than the capacitor itself. Also, there are internal components (i.e. the leads attaching to the 'plates') that will become limiting factors. All that to say, there's a physical limit to how much bigger you can make the cables and actually still attach them to the capacitor.

At some point, the thermal capacity of the cables will approach that of the brake discs of a normal car.

They rarely get hot enough to melt, even though they pretty much absorb the entire braking power.

I'd calculate the resistance of copper cables vs car mass and delta v, but I'm too lazy.

Could use higher voltages instead.

Not for supercaps, most have a breakdown voltage below 5 V.

That's not important, the batteries also explode if you take them over about 4.2v, you can stack them up to get the desired system voltage.

You can just stack supercaps in series to increase the voltage.

> Could this be used to charge your car's supercaps in 30s and have them feed into the batteries over a longer period of time?

Think about your question for a minute.

Buy a Tesla. It has an 85kWh battery. Now add about 100kWh worth of these supercapacitors because battery charging isn't 100% efficient and neither is discharging supercapacitors. Why would you want to haul around both 85kWh of batteries and 100kWh of supercaps when you can just bring 100kWh of supercaps?

100kWh in Supercapacitors would have an incredible mass for that much energy.

I see Supercaps are being more used for rapid discharges/re-gen periods. I.E. Tesla P100D (0-60 in 2.5sec) punching it would use the supercaps, and then going 100mph and letting regen take ahold, would also use the supercaps. The system would then balance out the power in the supercaps and what can be put into the battery for longer storage. Kind of like a crazy audio system. Has the supercaps that charge up for the bass hits.

Yes, of course. It would be eminently impractical to try and make a vehicle around supercaps at the moment. That's not the point I was trying to make, though. I was trying to point out the systematic error in thinking.

You've correctly pointed out that the supercaps are too big and heavy and such. But let's just imagine for a moment that they're made of magic and are 5% of the volume and 5% of the weight of batteries. It's still not a good idea to charge them up to then charge the batteries (from fixed charging stations) because then they're better than the batteries full stop. Throw away the batteries and use them the end.

The only way that they make sense is for what you've described, they're electrical buffers to help impedance match "slow" batteries with "fast" motors. But since that wasn't what the parent was asking, I didn't answer that question.

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