# Sodium-Air Battery Would Give Tesla Model S 9,000 Mile Range Per Charge



## EVDL Archive (Jul 26, 2007)

The trouble with sodium-air is its severely curtailed battery cycle life of just eight charges before it needs replacing.

More...


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## rochesterricer (Jan 5, 2011)

The article claims the Model S batter is 116Wh/kg, but the numbers I've seen say its somewhere around 220 or 240.


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## Ziggythewiz (May 16, 2010)

Not even worth reading with a title like that. When your cycle life is under 10 you don't need to be crunching numbers for automotive applications. 

Might make a great journalist taser though.


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## PhantomPholly (Aug 20, 2008)

Well, generally low cycle lifetimes have to do with crystallization or other such phenomena - and those sorts of problems are good targets for some of the emerging nanotech. I'm still sticking with my 2-year old prediction of us having cracked the chemistry by 2015 which will ultimately be our end solution - and this may be it.


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## ken will (Dec 19, 2009)

You can only recharge it 8 times, but at 9000 miles per charge that is still 72,000 miles.

My 1992 Ford Ranger has put on 31,000 miles in 20 years so at that rate a Sodium-Air battery would have to be replaced about every 40 years.

Not bad.


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## Ziggythewiz (May 16, 2010)

I assume that's if you have 1000 lbs of it. Obviously you're not going to build you car to have a range of 9000 miles on a charge if you don't even use that in a year.


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## Coulomb (Apr 22, 2009)

ken will said:


> You can only recharge it 8 times, but at 9000 miles per charge that is still 72,000 miles. ... Not bad.


Yes. And I wonder if you discharge it by only 1%, say after a week or two of driving (just like an ICE car), or even 0.1% by charging every day, maybe the cycle life will increase dramatically, so you don't need to replace the battery for the life of the car (or even the life of the owner).

Also, the capacity must be stupendous, such that a full charge from near flat would be (wild guess) something like a week of fast charging. Maybe for practicality you'd charge it over a month or so, every opportunity you get, and drive it between partial charges. But then you would still have an expensive month, where all your energy costs for a year or two would come at once. So again, better to recharge regularly, like present EVs.

This type of battery stores part of itself in the atmosphere, like gasoline. I suppose that's a major reason that it can compete with gasoline. Unlike gas, however, oxygen is returned to the atmosphere when the battery is recharged, and of course no CO2 comes into it at all.

The figures given above use the theoretical limits for sodium-air; a quick search reveals that although current sodium-air batteries have higher energy density than lithium-air, the theoretical limits for lithium-air are even better. So while where dreaming...


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## Coulomb (Apr 22, 2009)

Ziggythewiz said:


> I assume that's if you have 1000 lbs of it. Obviously you're not going to build you car to have a range of 9000 miles on a charge if you don't even use that in a year.


But unless the life issue is resolved, you may be forced to have such a large range, so you're not regularly replacing the battery.

But maybe it makes sense to make the battery easier to replace, and not carry around all that weight that you don't need. So then, replacing the battery might be a regular servicing event, like a 5000 or 10,000 mile service item. That might even bring the major auto manufacturers on board! Plus, you could possibly look forward to incremental advances in battery technology (less sag, more power, more life till the next service) every time you had this service done. This generates work for local people, instead of the bulk of the money likely going overseas for manufacture of one large battery. It would really depend on how quick, and therefore cheap, you could make the battery replacement process. It's a rather different scenario to what we're used to, but it might work out well.

[ Edit: following is wrong; see later post ]
Even if we don't progress much past the current 4000 mile range, to its theoretical maximum of 9000. 4/9ths of theoretical is pretty good for battery technology, isn't it?


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## Coulomb (Apr 22, 2009)

Coulomb said:


> Even if we don't progress much past the current 4000 mile range, to its theoretical maximum of 9000.


Looks like I misunderstood the article. It seems that the 4000 and 9000 figures are both theoretical, for sodium and lithium -air respectively.

They seem to talk about sodium as being the "current technology" because lithium-air suffers from really badly short life, something to do with O2- radicals (hope I got that right), and sodium-air doesn't have that problem, giving it the "long" life of 8 cycles (long relative only to lithium-air, of course, and that's if I understand the situation correctly).

So these figures are all theoretical, and they are already using the larger figure for lithium-air, which has huge technical problems to overcome. So no room for extra dreaming there.

That's not such a great picture after all, though of course it depends on what technological breakthroughs are made in the near future.


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## weber (Apr 22, 2009)

Having gone to the trouble of reading some of the source articles and investigating the authors self-confessed qualifications, my summary is that the author is extremely gullible and has just enough technical knowledge to be dangerous, or rather to waste a lot of readers' time. My estimation is that sodium air batteries are just one of the many battery types being researched that have maybe a 0.1 % chance of being viable for EVs in 20 years time.

I agree on one thing though. There's a good chance future EV batteries will use sodium in some way, simply because of its far greater abundance than lithium or any other metals with theoretical energy density between those of sodium and lithium. Although I'm thinking sodium-ion rather than the sodium metal required by sodium air batteries, due to the fire risk associated with all alkali metals.


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## JRP3 (Mar 7, 2008)

rochesterricer said:


> The article claims the Model S batter is 116Wh/kg, but the numbers I've seen say its somewhere around 220 or 240.


The cells are around 250 Wh/kg but the assembled pack is around 150Wh/kg.


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