Battery: the Lithium-Air revolution will not (possibly) take place ...

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Battery: the Lithium-Air revolution will not (possibly) take place ...




by Christophe » 10/10/17, 16:35

Small analyzes on the performance of the long-awaited Lithium Air battery ... a revolution that may not take place ... because its specific power is extremely low not compared to the best current batteries: up to 800 times less!

The single source of the numbers is Wikipedia. If you find others, post them here and correct them.

Taken from: transportation, electric / battery-toshiba-SCIB-recharged en 6-minutes-a-500kw-t15395.html

Li-air-support-discharge.jpg
Li-air-charge-discharge.jpg (281.19 KIO) Accessed 4494 times


About Lithium Air batteries, we have:

a) a mass energy that can compete to see exceed liquid fuels, all corrected returns, so excellent!

In theory, lithium-air batteries know how to store 3,5 kW.h / kg. However due to technological constraints (substrate, battery insulation ...), the actual energy density will most likely be lower. The density of 1,7 kW.h / kg supplied to the wheels can however be considered because of a better efficiency of the electric motors compared to the thermal engines


Source: https://fr.wikipedia.org/wiki/Accumulateur_lithium-air

b) mass power (and volume) very low compared to current Lithium batteries

low specific power (200 W / kg - 500 W / L)


Source: https://fr.wikipedia.org/wiki/Accumulat ... ithium-air

In comparison, some current Lipo (the best) can provide up to 95 times their peak current rating!

A current Lipo which is around 0.2 kWh / kg ...can therefore supply power to 95C of 19 kW / kg !!

It's really huge and it's 19 / 0.2 = 95 times what can provide a Lithium Air !! And 5 kg of battery can therefore provide, in peak, not far from 100 kW!


But ok at these levels of discharge current, it heats up a lot and the batteries do not last very long (200 300 max cycles) when they do not explode before ... but still ...

A lipo that would work in 5C (we find no below 15C on the market) which is very reasonable would provide a power of 0.2 * 5 = 1 kW / kg ... It is still 5 times more than a Lithium Air at the power level :(

This means that we will not be able to draw a lot of power per kg of lithium air battery: they will therefore be reserved ... for low power or static installations, which finally cancels all the benefit of an interesting mass energy :(

And to finish the comparative calculation, a Lithium Air can work with 200 / 1700 = 0.12 C ... it is 800 times less than a Lipo 95C ...

After the research ... but all the same ... the Lithium Air revolution will not be possible any time soon ... : Cry:
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Re: Battery: the Lithium-Air revolution will not (perhaps) not take place ...




by Christophe » 10/10/17, 17:02

This 2009 article does not mention the problem of mass power at all: https://www.usinenouvelle.com/article/l ... te.N120192
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Re: Battery: the Lithium-Air revolution will not (perhaps) not take place ...




by Gaston » 10/10/17, 17:06

One could imagine "mixed" batteries combining a (large) lithium-air with a (medium) Lithium-ion or even with a few supercapacitors.

The whole can provide a great power for a limited time and a modest power the rest of the time.

An "average" electric car requires a power of 20kW to drive at 110km / h on the motorway.
But she needs 50kW to climb the ribs (for a few minutes) and 100kW to start like a toll kéké (for less than a minute)

A Lithium-air battery of 150 kg (255 kWh anyway) could provide 30 kW continuously, enough to support a Li-ion battery of 50 kg (10kWh: about what is found in current rechargeable hybrids ) which would provide the accelerations.
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Re: Battery: the Lithium-Air revolution will not (perhaps) not take place ...




by Christophe » 10/10/17, 17:22

Gaston wrote:One could imagine "mixed" batteries combining a (large) lithium-air with a (medium) Lithium-ion or even with a few supercapacitors.


Yes, I was just thinking about it when I wrote the above message: finally making "hybrid" batteries where each battery would be used according to the demand for power / energy ... in short, take the best of each technology to make it an ultra global battery efficient in both power and energy ...

It's a good idea and the builders of "serious" EVs must already be on it (if not, uh, it's because they are big nazes ... sorry for the bit : Cheesy: ) ...

And with 250 kWh on board Li-Air (either enough to do more than 1000km ...) or the "energy" battery, one can easily imagine that this battery would gently recharge a "power" Lithium-ion. stopping the car (so as not to have to charge overall too often ...)
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Re: Battery: the Lithium-Air revolution will not (perhaps) not take place ...




by Gaston » 10/10/17, 17:52

Christophe wrote:And with 250 kWh on board Li-Air (either enough to do more than 1000km ...) or the "energy" battery, one can easily imagine that this battery would gently recharge a "power" Lithium-ion. stopping the car (so as not to have to charge overall too often ...)
It can even recharge by rolling whenever the power needed to advance is less than it can provide.
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Re: Battery: the Lithium-Air revolution will not (perhaps) not take place ...




by Christophe » 10/10/17, 17:57

Uh yes it is possible but it's still better off with a better controlled dump-load ... and more stable ...
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Re: Battery: the Lithium-Air revolution will not (perhaps) not take place ...




by ENERC » 10/10/17, 19:43

To have played a little with zinc / air batteries, the weak point is the cathode. The 1 / 2 O2 + H2O + 2e- → 2OH- reaction is very slow. And as soon as you draw power, the voltage drops.
Ok there is no water for lithium air (otherwise boom!), But you have to take oxygen in the air.

I start the calculation of the air volume for a power of 100 kW with a cell voltage of 4V:

100 * 1000 (Watt) / 4 (Volts) / 96500 (Coulomb -> mole) / 2 (2 electrons) * 22,4 (liter / mole) / 0,21 (O2 / air ratio) = 13,8 liters / second!

And it is actually much more seen that we can not take all the oxygen from the air at the cathode .... Otherwise the voltage drops and the current drops.
Clearly, techno metal / air are rather for high capacity / low current.
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Re: Battery: the Lithium-Air revolution will not (perhaps) not take place ...




by Christophe » 11/10/17, 01:47

Can you please detail the calculation of the necessary air volume?
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Re: Battery: the Lithium-Air revolution will not (perhaps) not take place ...




by ENERC » 11/10/17, 08:04

Can you please detail the calculation of the necessary air volume?


100 kW under 4V is 25 000 A (it is probably 250A under 400 V, but that does not change the calculation).

1 A is 1 Coulomb per second.
One mole is 96500 Coulomb.

25 000A requires 0,26 mole per second. (25 000 / 96500)
One mole of oxygen is 22,4 liters at normal pressure. But there is only 21% oxygen in the air.
Therefore 22,4 / 0,21 = 106 liters of air to have one mole of oxygen.

25 000A therefore require 0,26 * 106 = 27,6 liters of air per second.
But oxygen takes 2 electrons in the reaction, so divide by 2, or 13,8 liters per second.

Side surface, it is not better: it is considered that 100 mA cathX cm2 is already a very good value.
For 25 000A, you need 250 000 cm2 cathode, 25 m2.
And so house these 25 cathode m2 exposed to the air in the battery compartment ....
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Re: Battery: the Lithium-Air revolution will not (perhaps) not take place ...




by Christophe » 11/10/17, 11:25

Thank you for the details, I'm not used to turning amps into moles!

We can deduce that the lithium-air batteries will have to be coupled with sacred blowers ... and the filters that go with them to not pollute the cathode!

This will necessarily reduce the overall efficiency of the battery but given its potential it will still be interesting!

For the exposed cathode surface I think it's solvable quite easily not? With fine thin layer we can place a lot of exchange surface in a rather small volume ...
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