## BASF investigating sodium-air batteries as alternative to Li-air; patent application filed with USPTO

##### 06 December 2012
 Discharge–charge cycles of Na–O2 cells at various current densities (i.e., the rate capability). Cutoff potentials were set to 1.8 V for discharge and 3.6 V for charge. Dotted line: E0(NaO2) = 2.27 V. Hartmann et al. Click to enlarge.

In a paper in Nature Materials, a team of researchers from BASF SE and Justus-Liebig-Universität Gießen report on the performance of a sodium-air (sodium superoxide) cell. Their work, they suggest, demonstrates that substitution of lithium by sodium may offer an unexpected route towards rechargeable metal–air batteries. BASF SE has filed a Provisional Patent Application (US 61/615901) directed to sodium-oxygen cells as described in the paper with the US Patent and Trademark Office (USPTO).

While Li-air batteries have attracted a great deal of interest as future high-capacity systems ideal for longer-range electric vehicles, there remain a number of issues to be resolved, the authors note. (Earlier post.) Replacing lithium with sodium to build an analogous Na–O2 cell with sodium peroxide (Na2O2) as the discharge product offers the opportunity to construct a cell system with a high energy density (E0 = 2.33 V, wth = 1,605 Wh kg−1 (Na2O2). However, this system can also suffer from similar high overpotentials and low energy efficiencies when using carbonate-based sodium electrolytes.

In the search for room-temperature batteries with high energy densities, rechargeable metal–air (more precisely metal–oxygen) batteries are considered as particularly attractive owing to the simplicity of the underlying cell reaction at first glance. Atmospheric oxygen is used to form oxides during discharging, which—ideally—decompose reversibly during charging. Much work has been focused on aprotic Li–O2 cells (mostly with carbonate-based electrolytes and Li2O2 as a potential discharge product), where large overpotentials are observed and a complex cell chemistry is found. In fact, recent studies evidence that Li–O2 cells suffer from irreversible electrolyte decomposition during cycling.

...Interestingly, the reactivity of sodium and lithium towards oxygen is quite different despite their close chemical relation. Sodium can form a stable superoxide NaO2, whereas LiO2 is highly unstable and is found only as intermediate species in Li–O2 cells. Thus, in a Na–O2 cell, the formation of NaO2 (sodium superoxide) during discharge will compete with the formation of Na2O2. Moreover, even though peroxide formation is thermodynamically favored (E0 (Na2O2) = 2.33 V versus E0 (NaO2) = 2.27 V), the formation of NaO2 requires the transfer of only one electron per formula unit and will be kinetically preferred relative to the two-electron transfer towards the peroxide. Indeed, in an ether-based electrolyte we found solid NaO2 to be formed reversibly and exclusively (within the precision of our analytical methods) as a crystalline product at very low overpotentials.

—Hartmann et al.

 Detail sketch of the electrode assembly and the oxygen support (left). Magnified SEM image (right). Hartmann et al., SI. Click to enlarge.

The cell consisted of a metallic sodium anode, a glass fiber separator and a carbon-fiber gas diffusion layer (GDL) as the cathode. The electrolyte was a 0.5 M solution of sodium triflate salt (NaSO3CF3) in diethylene glycol dimethyl ether (DEGDME). The built an analogous Li–O2 cell (LiSO3CF3/DEGDME) for comparison.

We were successful in constructing a room-temperature sodium–oxygen cell with an ether-based electrolyte that achieved discharge capacities of over 300 mAh g−1 (carbon), corresponding to roughly 3.3 mAh cm−2 (electrode area). Cells could be cycled several times at current densities as high as 0.2 mA cm−2 using carbon with a specific surface area orders of magnitude smaller than in studies of Li–O2 cells.

As a major breakthrough we consider the very low overpotential of less than 200 mV during charging, which is at least a factor of 3–4 times lower than for any other Li–O2 or Na–O2 cell reported in the literature. The discharge product was unequivocally identified by XRD and Raman spectroscopy to be sodium superoxide (NaO2). The oxygen reduction reaction occurs as a single-electron transfer process (O2 + e → O2) and seems to be kinetically highly favored, which explains the reversibility of the cell reaction....The results demonstrate that the sodium-based cell chemistry might offer—compared with lithium-based cells—unexpected opportunities in the search for reversible energy storage devices.

—Hartmann et al.

Resources

• Pascal Hartmann, Conrad L. Bender, Miloš Vračar, Anna Katharina Dürr, Arnd Garsuch, Jürgen Janek & Philipp Adelhelm (2012) A rechargeable room-temperature sodium superoxide (NaO2) battery. Nature Materials doi: 10.1038/nmat3486

"..demonstrates that substitution of lithium by sodium may offer an unexpected route towards rechargeable metal–air batteries.." could be cheaper/safer.

a spring?

Once again we see that even IF there were such a thing as "peak lithium" we still have no reason to use it as a "show stopper" for BEVs.

@ai vin

Absolutely because the sales of BEVs are in the thousands instead of the billions due to high cost, short range, and long recharge time. Fix those problems and lithium will be in short supply particularly in the US which only has 2% of the world's reserve. It will be from the frying pan into the fire as far as US energy independence goes.

The 100 mile Nissan Leaf uses 4kg of lithium in its batteries. Let’s say magic happens and between 2015 and 2035 we put 1.2 billion 200 mile range EVs on the world’s roads, each using 8kg of lithium in their batteries. (And that's if range increase comes only from more batteries rather than the more likely improved anodes and cathodes.)

That would mean that in that 20 year period we would need to produce 480,000 metric tons of lithium per year.
And after that we could just recycle what we’ve already extracted.

At 20 mg lithium per kg of Earth's crust, lithium is the 25th most abundant element. Nickel and lead have about the same abundance.

Argentina, Australia, Brazil, Canada, China, Portugal and Zimbabwe have roughly 13,000,000 metric tons of lithium that can be extracted. That's a 27 year supply.

Bolivia has 5,400,000 tons. Over 11 years.

There are approximately 230,000,000,000 tons in seawater. A 479,167 year supply.

The cost of extracting lithium from seawater is 5x or less than from lithium salts.

Prices for high-purity, battery-grade lithium hydroxide range from $6,000 to$7,000 per tonne

http://lithiuminvestingnews.com/5886/lithium-prices-2012-carbonate-hydroxide-chloride/

That's $6 to$7 per kg (1,000 kg in tonne) or $24 to$35 for the lithium in a Leaf.

If we had to use seawater extracted seawater it would increase material costs by $120 to$140 for the entire battery pack.

And there's the recycling option....

Question, any rumor on energy density on a volumetric level? Kwh/Cm^3? or something along those lines...

This sounds like the future of EVs here...Lithium air has always been sort of a unicorn of sorts, good in therory but almost assuridly unattainable just from the chemisty standpoint.

Sodium seems like a real contender for EVs, and is actually quite prevalent in realiable energy storage... it is either this or we all use molten salt batteries...
Most of the Li-ion breakthoughs have major/cripling drawbacks, on a few key points( volume, power, weight, charges ect.) making them impractical.

I hope battieries can contend with the likes of H2 vehicles, but I also see the need for H2 in the long run. 300-400mile EVs will never be feasible, but an H2 car could refuel in mins without melting the powerlines. H2 can also be farmed using renewable resources(solar/ wind), or existing infrastructure(methane, grid electricity).(it could also be used as an energy sink/reserve during peak and off hours)

Kind of wish they would put more thought and time into H2, I see it as the future... and meandering around with batteries is just wasted time. EVs could never replace all of todays transit, H2 atleast has a fighting chance.
/rant

Can anyone tell me how much it would cost per mile to run a H2 fuel cell car, they are to be available from a number of manufacturers in 2015.
The Tesla model S has a range of 265 miles (EPA). Batteries would have to improve by 13.5% to get to the 300 miles figure that is considered impossible by some.Here in Britain petrol (GAS) costs £1.30 a litre (aprox.$8.80 a gallon). I have read that oil companies such as shell and BP are interested in selling Hydrogen but I don't think they plan to sell electricity to ev drivers. "300-400 mile EVs will never be feasible" 300-400 mile EVs aren't needed. As long as one can drive far enough to not be greatly inconvenienced by stopping for a rapid charge there's no need for longer range. 200 miles gets you over three hours of driving and the ability to drive over 500 miles with only two stops. The same number most people driving with liquid fuel would make. -- The batteries in the Tesla store 240 Wh/kg. Envia has a battery that stores 400 Wh/kg. That's 67% better. If anyone really wanted a 300-400 mile range the S with Envia-capacity batteries would give them 442 miles. -- The last I heard about the coming fuel cell cars is that one company is hoping to bring the cost down to$75,000.

I think what we're seeing with hydrogen and FCEVs is the run-on of a research program that started long ago and for which no one has had the good sense to shut it down.

Using renewable energy to crack out hydrogen is a very inefficient use of electricity that could be used much more efficiently in EVs/PHEVs.

The cost of infrastructure would be prohibitive when one considers that charging infrastructure is essentially in place.

For FCEVs to have a future they would have to be significantly cheaper to own and operate than EVs/PHEVs. I don't think that will be possible.

Dewent,

You can count on something like that $8.80 for a killogram of Hydrogen, but the fuel cell car will go farther. So, you might reduce your fuel bills, but the cost of the car would be higher. "$8.80 for a killogram of Hydrogen" from cracked water?

Hydrogen from methane gets us nowhere.

Bob there are plenty vehicles that are simply not viable on battery power... there is a need for vehicles to more than 3hrs 15mins on the freeway, EVs cannot address that.

you have to address a much larger problem than small personal transportation, several industries use ICEs to move product and people.

If all the ICEs(in transportation) suddenly vanished from the earth how would the world continue on? BEVs are great for city dwellers and those that have second vehicles. They may actually be great for 70% of the general population, but you cannot ignore the need for a solution that addresses range, scalability, and price.
Could you imagine the cost/weight/size of a BEV Tractor-Trailor capable of 500+mile trip?
Or patrol cars, ambulances, firetrucks, things that sometimes operate non-stop... I mentioned melting powerlines because its not rational to think that you could rapid charge something like a heavy duty truck possibly having over 500KwH of charge for a range of upto 150mi. Or more aptly 75 miles there and 75 miles straight back optimistically

(Envia's high capacity bateries are low current ones, you'd need almost a 200mi EV to have a car capable of highway travel.)

I am talking in extremes and maybe you missed that, BEVs are a step from removing the nation off of fossil fuels, but they are very far from a full solution. Even with perfect Li-Air and other technologies, they come up lacking.

Hydrogen because of its unique similarity to liquid fuels being able to stored and transfered rapidly, the ability to be simply generated with electrolysis, and its energy density being roughly 30%+ better than Lithium, sure it may not be as economical, but range becomes a non issue and you still have a vehicle that can be run on green electricity in the longrun... not to mention that studies/goals point to $30/kw fuelcell in 2017, and that tanks for the gas are getting cheaper and will scale more efficiently than batteries. http://www.hydrogen.energy.gov/pdfs/review12/fc000_papageorgopoulos_2012_o.pdf - snaged from davemarts post a while back The taxes in Derwent's country will probably be there for hydrogen as well as liquid fuel, someone has to pay for the roads. It takes more than 40 kWh to make one kilogram of hydrogen by electrolysis. Electricity in many places is 10-15 cents per kWh. That leaves us$4.00 to $6.00 just for the electricity, not to mention the chemicals, equipment, facilities, labor, profits, taxes and other factors. Bob there are plenty vehicles that are simply not viable on battery power... there is a need for vehicles to more than 3hrs 15mins on the freeway, EVs cannot address that. Examples? Could you imagine the cost/weight/size of a BEV Tractor-Trailor capable of 500+mile trip? No, what I imagine it using a 100 mile range tractor-trailer to haul between loading dock and rail terminal. Then electrified rail to do the long hauling. What I think will happen over the next few decades is that we will build a number of high speed rail routes in the US and late at night when passenger traffic is light those rapid routes will haul freight. It will be faster and cheaper than putting individual trucks on the road. In unique situations if it is really necessary to move more than 100 miles by truck then battery swapping is an option. Or, since it would be a very small percentage of all hauling, we might stick with diesel or use natural gas. However, I have been talking about personal transportation. Cars and light trucks. That's where we will most likely go electric first. Some larger vehicle applications might well be done with battery power. Fire engines don't really travel very far. If they did there would be nothing to put out by the time they got there. Same for ambulances, the majority make short runs and could be rapidly recharged after a run. We're already running city buses and garbage trucks with batteries. UPS, FedEx, Pepsi and other companies are doing some of their deliveries with battery powered trucks. Perhaps we'll see$30/kW fuel cells in 2017. If something like that happens and if we don't see higher capacity, cheaper batteries then perhaps hydrogen has a future. But remember, if EVs get embedded which will likely happen with solid 200 mile range at "gasmobile" prices FCEV vehicles would have to be significantly cheaper to own/operate to push EVs out of the market.

Manufactures would have to see FCEVs at a deep discount to EVs. That's pretty unlikely. And/or it would have to cost significantly less than 2 cents per mile to drive a FCEV. That certainly seems unlikely when one looks at the inefficiency of cracking water.

If FCEVs cost about the same as EVs and if they cost about the same per mile they won't survive. It would take billions to create the fueling infrastructure and there would be no financial reason to do so.

"Kind of wish they would put more thought and time into H2, I see it as the future..."

Yes, hydrogen is the fuel of the future and it will always be the fuel of the future.

With low cost 600 to 1000+ Wh/Kg batteries by 2020/2022 or so, many people will stop talking about ICEVs, FCEVs, HEVs, and PHEVs and will concentrate on future extended range EVs.

Very large vehicles may be the exception. They will either stay with improved Diesel or progressively switch to FCEVs?

You dont need big batteries for trucks either, install high frequency wireless power transfer pads under the highway and recharge the vehicles as they drive by. If you want to spend more money and feel green then install solar panels by the side of the road.

S.Korea has been working on that and has a test road, Germany has a project with overhead power lines for trucks.

Someone has already built an "18 wheeler" with a 100 mile range.

If batteries go from the current 'just above' 100 Wh/kg to over 500 then battery swapping would work fine.

Move the vast majority of our freight to electrified rail.

Wiring the road would be pretty expensive.

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