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Research team demonstrates Li-air battery capable of long cycle life

A team from Hanyang University (Korea) and University of Rome Sapienza (Italy) have demonstrated a lithium–air battery capable of operating over many cycles with capacity and rate values as high as 5,000 mAh gcarbon−1 and 3 A gcarbon−1, respectively. The team, led by Yang-Kook Sun and Bruno Scrosati, reports on their work in a paper in the journal Nature Chemistry.

Despite the extreme promise of lithium-air batteries—with estimates of energy densities some 10x those of current Li-ion batteries—the performance of Li-air batteries has been limited to only a few charge-discharge cycles, with low rate capability, the team notes.

Researchers suspects these issues may be connected to lithium oxidation products and intermediates, including Li2O2 and an anionic oxygen radical, O2·, a reactive species which decomposes typical electrolytes such as organic carbonate solutions of lithium compounds.

The team selected tetra(ethylene glycol) dimethyl ether-trifluoromethanesulfonate (TEGDME-LiCF3SO3, or TEGDME-lithium triflate) for use as a stable electrolyte, and reported that preliminary data showed evidence of reversible formation of Li2O2, fast kinetics and almost no degradation of performance for more than 100 cycles. The researchers suggested that the enhanced stability may be due to a fleeting oxygen radical lifetime in their electrolyte.

Resources

  • Hun-Gi Jung, Jusef Hassoun, Jin-Bum Park, Yang-Kook Sun & Bruno Scrosati (2012) An improved high-performance lithium–air battery. Nature Chemistry doi: 10.1038/nchem.137610.1038/nchem.1376

Comments

Zhukova

This would be impressive. With 5000 mAh/g and 3 A/g for carbon, assuming the carbon is 10% the mass of the battery, it may lead to 10-year, 700 mile range, 300 hp, 200 kg car battery.

Herm

lets hope that mouthful of an electrolyte is not more expensive than gold.

Davemart

All those constituents of the electrolyte are cheap as chips, although not so tasty! ;-)

Could someone translate what the rate values mean in terms of power density for non-engineering folk like me?

kelly

Make it so..

Davemart

Trying to understand what Zhukova tells us, 300 hp is around 225kw, so the 200 kg battery he refers to has a power density of about 1.1 kw/kg.

Zhukova

If you click on the link to the Chemestry journal reference, you will find som additional charts. At the bootom of that page is also a link for a pdf file with "Supplementary information" This pdf file has photos of their disassembled test battery. It shows the carbon cathode and lithium anode. The file also has graphs showing the capacity of the carbon without their electrolyte and others with it. The difference is extreme!

I assumed the carbon would be about 10% the mass of the battery, but it's just a guess. If it's close, and the Li anode supports the same current density, then 3 A/g is a lot of current. A 200 kg battery would have 20 kg of carbon. So 20,000 grams x 3 A/gram is 60,000 amps. The voltage is 2-3 volts. 60,000 A x 2.5 V = 150,000 Watts, which is 200 hp.

It's a simple analysis, but this battery seems much better performance than previous Li-Air batteris, especially with the current density and cycle lifetime.

HarveyD

Eventually (by 2020 or soon thereafter) the power density of batteries and e-power trains will compete will current ICE equivalent and even better. EVs equipped with a 100+ Kwh light weight battery pack and ultra quick charging facilities (5 minutes) will push the best ICE vehicles to the graveyard and/or museums.

Many EV owners will recharge once a week or so.

Davemart

@Zhukova:
Many thanks.
Now I am not sure about how you arrive at 700 miles of range, as the energy calculation is also beyond me.
If you have time I would be grateful if you would explain, but thanks in any case for the explanations you have provided so far.

DaveD

Wow, impressive. We're still at least 5-10 years out for Li-air batteries becoming mainstream...if ever. There is always some devil in the details that may prevent this from being practical in the real world.

But I wouldn't have expected to see something like this for another 5 years either, even in lab samples, so maybe we can hope for a miracle

:-)

Davemart

'the technology faces substantial challenges for commercialization. These include poor cyclability (up to only tens of cycles); reversibility; low energy efficiencies, with charging voltages as high as 4.0–4.5 V and discharge voltages of about 2.5–3.0 V; and low power densities.'

http://www.greencarcongress.com/2011/11/mo-20111126.html

This seems to address low power densities and cyclability.
Am I correct in thinking that if you charge at 4.0-4.5V and discharge at 2.5V or so then you have made an efficiency loss of around 40%?

Zhukova

If you're bold enough to purchase the article from Nature, it's very interesting and has very much detail on the experimental conditions, chemical equations, and lots of graphs. The electron scanning photos show particle sizes before charging, while charged, and after discharge, which are very interesting.

But the main thing is the authors' conclusion:

"It is worth noting that the lithium–oxygen battery reported here can operate under capacity levels as high as 5,000 mAh g(carbon) with an average discharge voltage of 2.7 V, leading to a very high theoretical energy density of 13,500 Wh kg. Even assuming a reduction factor of one order of magnitude due to the weight of the ancillary components, such as the cell case, current collectors and electrolyte, the practical energy density may be estimated at a value much higher than that offered by the present lithium-ion battery technology. Furthermore, the battery is expected to be stable under various cycling regimes, to have a low cost and to be compatible with the environment."

A one-magnitude reduction factor would still give 1,300 Wh/kg. Envia's silicon anode battery has something like 400 Wh/kg.

If the battery weighs 200 kg, 1300 Wh/kg x 200kg = 260 kWh. If the car can travel 3 miles per kwh (like the Nissan Leaf), you get more than 700 miles.

Davemart

Zhukova:
Great stuff!

The chief remaining obstacle on the face of it is charge voltage.

Zhukova

According to the authors' conclusion, it appears my initial estimate of the carbon cathode comprising 10% of the mass of the battery was pretty close. This is because they assume an order of magnitude reduction factor, which implies 10%. They also seem to agree that nothing in the battery limits the energy capacity to less than that of the carbon cathode. So the 260 kWh for a 200 kg battery seems feasible.

You only need about 20 hp to maintain 60 mph in a car. So you might think that a 200 kg, 700 mile battery isn't necessary. However, at 3 A/g, you would get only about 30 hp and 70 miles for a 20 kg battery. You need more hp for acceleration, so you would need more grams of carbon, which also give more range. 100 kg, 350 mile, 100 hp battery would work for most people, and this one seems like it would do the job.

Darius

'700 mile' seems practical than 350. In 700 mile option there will be no need for fast charging. Would be enaugh to have overnight charging option and would be no any range anxiety issue. Since active element volume and cost could be the same as it is now or arround 30% of the pack the optimum could be arround 200 kg in any case.

twitter.com/siromega

A 700 mile battery that lasted 100 cycles would be a 70,000 mile battery. They really only would need to get to 225 cycles to get a 150,000 mile battery, which should (hopefully) be sufficient for most car owners to realize ROI before they have to replace it. The above article doesn't say much about degradation above 100 cycles, so I cant really make any assumptions beyond that. Having a 700 mile range really destroys any range anxiety issues - though even a 90kW "supercharger" would take 2.5 hours to fully charge the battery. It might be OK if you're driving somewhere for a sports event, but not for a pit stop somwhere.

Zhukova

@Davemart
Energy = Voltage x Current x time. I don't think the difference in charging and discharging voltages determines efficiency. For the same charge and discharge energy, the voltage and current are inversely proportional (for fixed duration of time).

However, the authors claim there are no side-decomposition reactions, which would probably equate to an energy loss, and that the electrolyte chemical inertia is very stable. They don't address efficiency, but all batteries have resistive loss. They also say that 4.5 V is below the breakdown voltage of the electrolyte, which would limit charging current and time.

Davemart

@Zhukova:
Many thanks again.

I would like the 500 mile version, please, sent COD! ;-)
Around 150hp or so is plenty for the power hungry, a 500 mile range battery could be kept comfortably between 20-80% charge almost all of the time so reducing battery degradation, and if you drive 500 miles you need a break anyway.

You are still only talking about half the weight of the Leaf battery, and some serious weight reductions in the rest of the car, along the lines of the Toyota FT-Bh should improve performance and reduce pack sizes and cost still more.

MG

@Zhukova,
In the paper, does it say anything about self-discharge rate?
It's important for batteries with limited cycle life, not to get quickly discharged if driven little in days after a full charge.

Davemart

@siromega:
They normally only test prototype batteries out to 100 cycles, so not much should be read into that.

However, they state that there is 'almost no degradation' over the 100 cycles, and it would be very unusual, indeed AFAIK unique, if it were to suddenly drop off a cliff.
Something on the order of 1,000-5,000 cycles down to 80% capacity might be likely, but of course many further tests will need to be done.

Zhukova

@MG
I didn't read see anything in the paper about self-discharge. However, this is one thing that concerns me with the need to have a 500-mile battery. People rarely drive 500 miles in one day. So most of the time the battery is self-discharging a lot because it's big. Small batteries self-discharge at the same rate, but in this case size matters! I mean the total energy lost is proportional to the size of the battery.

One good thing about gasoline is that it flows easily through a tube into the fuel tank. I rarely have more than 100 miles of gas in my car because I never go anywhere. Putting extra batteries in a car for a long distance trip would be a lot more difficult than just filling up at the gas pump. The alternative is to carry the mostly dead weight of a 200 kg battery, which self-discharges a lot.

I don't know if people would accept an infrustructure design where BEVs have small batteries and quick chargers are everywhere. Now we have gas stations everywhere, but people still want 500-mile range in their ICE vehicles.

DaveD

Zhokova,

The 700 mile range worries me because of cost and self discharge reasons.

Wouldn't it be easier to mix in some LiFePo cells for a hybrid type battery? A123 came up with some cells that provide 20kW/kg cells for F1 so it can be done.

10-20kg of LiFePo to handle acceleration and regen, and maybe 50-100kg of some of these Li-air for the desired range you want? Seems like a good combination to me.

I know that rapid charging is still an issue, but there is a sizable part of the population that just doesn't try to drive 1,000 miles in a day and that would be happy to stop every 5 hours and eat/rest while the car charged for an hour or so.

Roger Pham

Regarding the range, power density, and self-discharging problem, all these can be solved by the use of:
1) an intermediate high-power-density battery for acceleration and braking energy recuperation,
2) modular Li-Air batteries in which multiple battery modules can be quickly installed and removed. Each module may provide a range of ~100 miles and can be stacked one on top of each other to provide more range as desired, or removed to reduce weight, self-discharging losses, and increase in cargo capacity and space.
3) Better-Place arrangement for swapping or rental of additional battery modules for long-distance trips.

This is a very exciting development and can really be a game changer that can encourage much more rapid renewable energy penetration. This type of capacity in a low-cost battery with high cycle life will spell V2G ad nauseum to soak up all the excess solar and wind electricity to release at another time and make money in the process that will help pay for the cost of the battery. Harvey D's dream may come true: People may ditch their ICEV and rush out to get a BEV with Li-Air battery en masse so that they can really save on transportation costs!

ChrisL

I don't think it's actually necessary to decide what range these batteries should support. Hopefully car manufacturers will build variety of cars to match what different people want: long range highway cruiser for people who want that, light-weight 100-mile city/commuter cars for people who never drive more than 50 miles a day (or have another car for long-range duties), etc. I'd like for there to be a choice; hopefully this battery chemistry will support a range of sizes.

Engineer-Poet

What self-discharge?  People, this is a lithium-air battery; if you want it to stop discharging, you close the air valves.

Zhukova

Ideally, one would like to be able to do 0-60 in .8 seconds and 7.8 sec, 168 mph quarter mile, like the Killacycle -

http://www.youtube.com/watch?v=tRpMV-Gf0hA

I doubt a 500 hp Li-Air battery would fit in a bike dragster. Killacycle uses 1,210 A123 M1 Nanophosphate Li-Ion battery cells.

Anyway, it seems to me a hybrid battery would be best for cars, with Li-Ion or supercapacitor for acceleration, and Li-Air for modest range. It seems like batteries could be made portable enough to be easily installed and removed for long trips.

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