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Graphene-based supercapacitor offers energy density comparable to NiMH battery, but with rapid charge and discharge

26 November 2010

Graphenesupercap1
Ragone plot of graphene supercapacitor. Credit: ACS, Liu et al. Click to enlarge.

Researchers from Nanotek Instruments and Angstron Materials have developed a graphene-based supercapacitor that exhibits a specific energy density of 85.6 Wh/kg at room temperature and 136 Wh/kg at 80 °C (all based on the total electrode weight), measured at a current density of 1 A/g. These values are comparable to those of NiMH batteries, the researchers note, but the new supercapacitor offers the ability to be charged or discharged within seconds or minutes. A paper on their work was published online in the ACS journal Nano Letters.

These are the highest energy density values ever reported with carbon electrodes without the pseudocapacitance contributions from a conducting polymer or metal oxide, the authors said, further stating that “We believe that this is truly a breakthrough in energy technology.”

The group, led by Bor Jang of Nanotek Instruments, reported in 2006 that graphene can be used as a supercapacitor electrode material. Despite a number of efforts to improve the specific capacitance of graphene-based electrodes, however, results fell sort of the theoretical capacitance of 550 F/g due to the high tendency for graphene sheets to re-stack together.

The team determined that the best strategy to achieve a high capacitance in such graphene-based electrodes is to use curved graphene sheets rather than flat sheets to prevent the sheets from sticking to one another face-to-face. The curved morphology enables the formation of mesopores accessible to and wettable by environmentally benign ionic liquids capable of operating at a voltage >4 V.

With the total electrode weight of a supercapacitor system being typically one-fourth to one-half of the total system weight, the system-level specific energy of graphene-based supercapacitors can exceed 21.4-42.8 Wh/kg, which is comparable to that of a modern nickel metal hydride battery used in a hybrid vehicle. This breakthrough energy storage device is made possible by the high intrinsic capacitance and the exceptionally high specific surface area that can be readily accessed and wetted by an ionic liquid electrolyte capable of operating at a high voltage.

—Liu et al.

Resources

  • Chenguang Liu, Zhenning Yu, David Neff, Aruna Zhamu, and Bor Z. Jang (2010) Graphene-Based Supercapacitor with an Ultrahigh Energy Density. Nano Letters doi: 10.1021/nl102661q

November 26, 2010 in Batteries | Permalink | Comments (41) | TrackBack (0)

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Spectacular of course. I'd be curious to hear about the projected cost of this capacitor.

Most Graphenes are currently very expensive as are most new breakthrough technologies or materials. When mass produced, price will quickly drop. Both ultra capacitors and next generation batteries could make use of this material to achieve higher performances.

E-storage units will evolve much faster in coming years with more R&D and as demand multiplies. Price per Kwh will go down with mass production facilities in many countries.

The current decade may very be called the e-storage units golden years or decade. We will all be surprised at what will be available in 2020+.

Other new technologies such as high performance 3D TVs, low cost color e-books, higher performance lower cost solar cells etc may be overshadowed by high performance, highway capable, lower cost BEVs by the end of the current decade.

This is REALLY BIG NEWS.

EVs were good enough with NiMh batteries.
86wh/kg is not that bad at all considering the features. Li-io tech is only between 150 and 250 wh/kg.

If this capacitor is comparable to other supercapacitors, then an EV with this would:
- Accelerate like a rocket (great power density)
- Never require battery replacement
- Regenerate 90% of braking energy

@joewilder
It seems that graphene will be cheap to produce:
http://www.physorg.com/news187448260.html

This is REALLY BIG NEWS.

EVs were good enough with NiMh batteries.
86wh/kg is not that bad at all considering the features. Li-io tech is only between 150 and 250 wh/kg.

If this capacitor is comparable to other supercapacitors, then an EV with this would:
- Accelerate like a rocket (great power density)
- Never require battery replacement
- Regenerate 90% of braking energy

@joewilder
It seems that graphene will be cheap to produce:
http://www.physorg.com/news187448260.html

An other article about the cheap production of graphene:

http://www.greenoptimistic.com/2010/06/10/victor-aristov-graphene-production-technology/

Outstanding performance which is above NiMH level(>130 kW/kg) and hopefully GM/Oil can't bury.

In mass production, this electric storage could be a fraction the weight and cost of present alternatives.

Imagine zipping between malls and McD charge stations/plugins with E-bike/light vehicle 1-2 minute charging free, indefinitely, and nearly maintenance-free.

If true, watch for massive illegal big auto/oil actions attacking this transportation advance.

Like murdering 123 medically uninsured Americans daily, the US has the $100's/hr criminal lawyers and politicians to 'get er done'.

I suppose you wouldn't actually need as much capacity with a storage device you could refill instantly. 6 Kwh or so might be enough for people that live in town.

I've wanted to say this fore years and it still might be a bit premature but.....

Game Over

This is a huge breakthrough. Even if the cost seems high upfront, the high cycle nature of supercapacitors makes them financeable.

I suppose you wouldn't actually need as much capacity with a storage device you could refill instantly. 6 Kwh or so might be enough for people that live in town.

Don't forget that this is a supercapacitor. A supercapacitor can be discharged down to zero without damage while with a battery you only have a DOD of 80%, so a 6kwh SC is like having a 7.5kwh battery.

One drawback seems to be capacity dependence on ambient temperature but that may be solved with good insulation and it may not a problem at all for warm climates.

If the cycle life is similar to normal supercaps (in the millions) we have a HUGE breakthrough here because the BIGGEST problem of EV batteries are solved:
- low cycle life
- slow recharge / low brake regeneration ration

The relatively low energy density is NOT a very big problem because it can be circumvented with good engineering and organizational solutions.

Moreover, the NiMh-class energy density was obviously enough for a lot of people (EVa, Rav4EV)

And if the low-cost graphene productions work out (which does seem to be the case), we also solve the problem of EXPENSIVE batteries.

Uhm, I mean "production".

This energy density is about the same as Altairnano's (45 wh/kg) Titanium quick-charging Li-Ion batteries, which also have long life. But, it seems like the graphene capacitor would have deeper discharge and lower cost.

We need way much more information to judge. Information needed on cost and cycling. If it really so as it is described in the paper immediate actions needed from government, investors, public. EEstor blog shall be replaced with new one (joke).

I predict that we will never hear of EEStor again. ;-)

What's EESTOR? ;-)

"85.6 Wh/kg at room temperature and 136 Wh/kg at 80 °C"

Should one infer that performance continues to drop with ambient temperature?

Do UCs generate heat while discharging as some batteries do?

In order to extend range would it make sense to super-insulate the capacitor pack and heat it up?

---

And with the ability to charge very rapidly, it would seem that a ~50 mile range would be fine for many drivers, especially two-car households. One would not need to be too concerned if they could fill up during a very short stop. (Bring on the robotic chargers.)

@ai_vin,

"A supercapacitor can be discharged down to zero without damage..."

In theory it's true, but don't forget that voltage of capacitor drops during discharge process. Li-Ion batteries (and I guess Li-Po ones) voltage drop per cell maybe from 4.0 Volt to 3.4 Volt, as SOC goes from 90% to 20%. Depends on technology, those from EnerDell had lower value, would drop to 1.8 V.
Energy contained in capacitors is given by formula: W = 1/2 C* V^2.
This applies to linear capacitors, ie where capacitance is voltage independent, but we don't know almost anything of these graphene capacitors.
So when voltage drops to 50%, only 25% energy remains.
When 80% energy is used up, voltage drops to 45%.
In order to handle the widely variable input voltage, more complex (and expensive) power electronics is needed.
How far low (in voltage terms) to go, will be dictated by the price of installed capacitive storage and extra cost for wide-range power converter.

SAFETY?? And within the system - not as spectacular:

"the system-level specific energy of graphene-based supercapacitors can exceed 21.4-42.8 Wh/kg..."

Still, looks promising.

Yes, that implies that capacity drops with lower temperature.

So this may not be ideal for cold climates or needs extra measures to keep it warm. However, this may not be an insurmountable challenge. The Xebra battery has similar issue.

Power electronics to handle a 50% + voltage drop should not be a major challenge. Inverters can be built to handle that and much more.

The real challenges are:

- high enough energy density
- quicker charge/discharge time
- lower cost.
- improved durability.

Graphene ultra caps (or batteries with similar technologies) could address all the above before 2020. That would mean the end of ICE cars and small trucks.

This is good stuff. If we have enough labs working in the right directions, it is amazing what they come up with. Now if they can commercialize this we are off to the races.

If something sounds too good to be true... Wow, lots of people jumping the gun on this. IT'S A PAPER. Wait until it's been proven through real life testing and extensive abuse before declaring the end of all other storage regimes.

Yes, this is promising and exciting. Don't forget, it's still in the laboratory stage. Cost, durability, safety, scalability, constructability, cold weather performance... lots to be verified before this can be considered a real technology.

My caution aside, it sure seems like a good UC like this could mate well to a bank of batteries to allow better regen from braking.

Great to see such technological development being done in the heart of the rust belt. No shortage of nearby available manufacturing facilities eager to turn research into production reality. Hope they can do that quickly.

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