Metal - Air Batteries

[Alan de Enfield]

Just been reading up on the next 'big breakthrough' in batteries - particularly 'Aluminium - Air'

 

Al-Air Time line - practical usage is getting closer :

 

 

Batteries	Theoretical Voltage (V)	Theoretical specific capacity (Ah Kg−1)	Theoretical energy density (kWh kg−1)	Practical operating voltage (V)
Li–air	3.4	1170	13.0	2.4
Zn–air	1.6	658	1.3	1.0–1.2
Mg–air	3.1	920	6.8	1.2–1.4
Na–air	2.3	687	1.6	2.3
Al–air	2.7	1030	8.1	1.2–1.6   Among the metal–air batteries shown in Table 1, the Li–air battery shows the highest theoretical energy density (13000 Wh kg−1), which is significantly greater than other rechargeable battery technologies [13], [14]. Nonetheless, rechargeable Li–air batteries still have many challenges to overcome such as the blocking of porous carbon cathodes by discharge products, instability of lithium in humid environments [15], insufficient understanding of catalytic mechanism [16], low electrochemical efficiency owing to high charging overpotentials...…………………………….   https://www.sciencedirect.com/science/article/pii/S246802571730081X

[dor]

My hearing aid batteries are metal - air.  Not sure what the metals are, I thought they were zinc - air, but the packaging gives mercury and lead as potential pollutants.

 

They are activated by peeling off a small sticker which allows air to enter the battery through holes in the base.  Not rechargeable of course.

[Dr Bob]

Wow, it mentions ionic liquids. They are mega expensive and I mean mega. You would only use them if no other option. That sort of suggests the other solutions don't work? Interesting stuff.

[MtB]

11 minutes ago, Dr Bob said:

Wow, it mentions ionic liquids. They are mega expensive and I mean mega.

 

What, like even more expensive than Hobgoblin or Bishop's Tipple?

[rusty69]

3 hours ago, Mike the Boilerman said:

 

What, like even more expensive than Hobgoblin or Bishop's Tipple?

I c wot u did

[Dr Bob]

I do like hobgoblin gold.

[cuthound]

I saw a working prototype back in around 1985, for a telecoms application to replace both standby generator and UPS (Uninteruptible Power System).

 

They talked of its suitability for EV's even back then even back then, once issues productionising them were resolved.

 

Although a primary cell, therefore not rechargeable, the aluminium anodes can be replaced once when exhausted, before the battery must be  completely recycled. Over 97% of the materials used in the prototype I saw were fully recyclable.

 

However like hydrogen fuel cells all/air batteries seem to be tsking a long time to productionise.

 

Is this because of technical difficulties to be overcome or a desire to fully exploit existing technologies first? Who knows.

[IanD]

It's because they're primary cells; having to replace the aluminium anodes after one use and recycle the entire battery after two uses is fine for applications like standby generators and UPS which only have to run once in a blue moon (or UAV where energy density beats everything else), but makes them impractical for applications like cars (and boats) where you want a life of thousands of cycles. Low-cost lithium-ion batteries are a far better solution, especially when they become cost-competitive with lead-acid -- which probably won't be very long because the cost is being driven down by BEV and power storage applications.

 

Also the cost of battery recycling is likely to make nonsense of the economics of using low-cost electricity as a primary energy source.

 

And if you think lack of battery charging stations is bad, imagine the problem of running out of power and needing a new battery before you can move again...

Edited July 10, 2018 by IanD

[cuthound]

3 hours ago, IanD said:

It's because they're primary cells; having to replace the aluminium anodes after one use and recycle the entire battery after two uses is fine for applications like standby generators and UPS which only have to run once in a blue moon (or UAV where energy density beats everything else), but makes them impractical for applications like cars (and boats) where you want a life of thousands of cycles. Low-cost lithium-ion batteries are a far better solution, especially when they become cost-competitive with lead-acid -- which probably won't be very long because the cost is being driven down by BEV and power storage applications.

 

Also the cost of battery recycling is likely to make nonsense of the economics of using low-cost electricity as a primary energy source.

 

And if you think lack of battery charging stations is bad, imagine the problem of running out of power and needing a new battery before you can move again...

 

Surely just changing one or more standard sized batteries over can be made practical, especially given the energy density of 13000wh/kg compared to an average of 200wh/kg for lithium ion.

 

In the telecoms industry,  they standardised 50 volt, 100 amp output rectifiers decades ago, using quick fit connectors. A rectifier weighing 25kg can be changed in about one minute, so I'm sure this type of connector could be used on batteries.

 

This will be quicker than any battery can be charged. Hopefully by the time the internal combustion engine is consigned to history we will have changed our society from a throw away culture to one that embraces recycling.

Edited July 10, 2018 by cuthound
To add the last sentance

[IanD]

19 hours ago, cuthound said:

 

Surely just changing one or more standard sized batteries over can be made practical, especially given the energy density of 13000wh/kg compared to an average of 200wh/kg for lithium ion.

 

In the telecoms industry,  they standardised 50 volt, 100 amp output rectifiers decades ago, using quick fit connectors. A rectifier weighing 25kg can be changed in about one minute, so I'm sure this type of connector could be used on batteries.

 

This will be quicker than any battery can be charged. Hopefully by the time the internal combustion engine is consigned to history we will have changed our society from a throw away culture to one that embraces recycling.

You're comparing apples to oranges; the theoretical energy density for Al-air might be 8kWh/kg, but in practice 1300Wh/kg is currently achievable. The cost of the batteries is high, and the overall cycle efficiency (including manufacture/anode replacement) is about 15% which is similar to or worse than internal combustion engines and far worse than rechargeable batteries.

 

The 200Wh/kg is for real lithium-ion batteries which can be recharged thousands of times, giving much lower manufacture/running costs than Al-air and more importantly much higher overall energy efficiency. It's exactly the same problem as hydrogen-powered cars -- looks attractive for range and emissions but makes no sense when you look at the overall efficiency and cost.

 

The only thing Al-air has in its favour is >5x longer range than Li-ion; in all other aspects (initial and running costs, efficiency, environmental impact, no recharging capability) it is far worse.

 

Given that overall energy efficiency of transport is now a high priority for all governments -- either to reduce CO2 emissions if the final energy source is fossil fuel, or to minimise the amount of renewable power capacity needed -- it's inconceivable that any system with similar or lower efficiency than conventional internal combustion engines will be widely adopted. Which means rechargeable BEV of one sort or another (e.g. Li-ion) will be, but primary cell BEV (like Al-air) won't be.