View Full Version : Rechargeable Zinc-Air battery moves closer to commercialization
son_of_flubber
September 27th 18, 04:06 PM
https://www.nytimes.com/2018/09/26/business/energy-environment/zinc-battery-solar-power.html
September 27th 18, 05:12 PM
On Thursday, September 27, 2018 at 10:06:46 AM UTC-4, son_of_flubber wrote:
> https://www.nytimes.com/2018/09/26/business/energy-environment/zinc-battery-solar-power.html
If it is as "simple" as claimed, why is the circuit board (seen in the photos in the article) so complicated?  Also, this has been in development for some years, so clearly there are some significant obstacles (see here: https://en.wikipedia.org/wiki/Zinc%E2%80%93air_battery#Secondary_%28rechargeable %29 ).  If they've solved them, cool!
Martin Gregorie[_6_]
September 27th 18, 06:40 PM
On Thu, 27 Sep 2018 08:12:09 -0700, moshe.braner wrote:
> On Thursday, September 27, 2018 at 10:06:46 AM UTC-4, son_of_flubber
> wrote:
>> https://www.nytimes.com/2018/09/26/business/energy-environment/zinc-
battery-solar-power.html
> 
> If it is as "simple" as claimed, why is the circuit board (seen in the
> photos in the article) so complicated?  Also, this has been in
> development for some years, so clearly there are some significant
> obstacles (see here:
> https://en.wikipedia.org/wiki/
Zinc%E2%80%93air_battery#Secondary_%28rechargeable %29
> ).  If they've solved them, cool!
I notice the article doesn't mention the energy density, capacity or 
charge/discharge rates of that battery. Without this info we can't know 
whether this technology is only useful for powering lightbulbs, radio 
repeaters etc. or if it has enough grunt to run a car or an FES system.
In this the NY Times is, little better than New Scientist, which 
periodically talks up some doctoral student's new, lab-scale battery 
technology that, thesis written, is never heard of again. 
-- 
Martin    | martin at
Gregorie  | gregorie dot org
September 28th 18, 12:00 AM
"....which periodically talks up some doctoral student's new, lab-scale battery 
technology that, thesis written, is never heard of again."
That also describes "Gliding International" when it comes to battery technology, electric airplanes and the like.
RW[_2_]
September 28th 18, 08:09 AM
On Thursday, September 27, 2018 at 6:00:40 PM UTC-4,  wrote:
> "....which periodically talks up some doctoral student's new, lab-scale battery 
> technology that, thesis written, is never heard of again."
> 
> That also describes "Gliding International" when it comes to battery technology, electric airplanes and the like.
Ultra capacitors !
Soartech
September 28th 18, 04:48 PM
> Ultra capacitors !
  A gallon of gasoline contains 120 million Joules of energy.
Now use this website to calculate what size ultra capacitor you would
need to achieve this amount.
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capeng.html
Dave Nadler
September 28th 18, 05:49 PM
Try a dose of reality:
https://www.youtube.com/watch?v=JELNfk-_0Dg&feature=youtu.be
Martin Gregorie[_6_]
September 28th 18, 05:58 PM
On Fri, 28 Sep 2018 07:48:13 -0700, Soartech wrote:
>> Ultra capacitors !
>   A gallon of gasoline contains 120 million Joules of energy.
>
A more useful equivalent for comparison is that a litre of petrol is  as 
near as dammit 10 kWh in energy terms - and petrol spiked with methanol 
will be a bit less: 9-9.5 kWh at a guess,
So a US gallon (3.78l) would be the equivalent of 37.8 kWh of 
unadulterated petrol or 34-36 kWh if its a gasoline/methanol blend.
By comparison, the Gen 2 FES battery has 14 cells, each of 2.1 kWh, or 
29.4 kWh for the standard 14 cell pack, so an hPh Shark (dual packs 
carried has just less than 60kWh of energy onboard, or 1.6 US gallons of 
avgas equivalent. 
The dual packs are about 18 litres total volume, so on a volumetric basis 
they're about 1/3 as good as petrol when it comes to storing energy in 
limited space.
-- 
Martin    | martin at
Gregorie  | gregorie dot org
Dan Marotta
September 28th 18, 06:09 PM
Dammit, I hate it when someone uses math to prove a point... :-D
On 9/28/2018 9:58 AM, Martin Gregorie wrote:
> On Fri, 28 Sep 2018 07:48:13 -0700, Soartech wrote:
>
>>> Ultra capacitors !
>>    A gallon of gasoline contains 120 million Joules of energy.
>>
> A more useful equivalent for comparison is that a litre of petrol is  as
> near as dammit 10 kWh in energy terms - and petrol spiked with methanol
> will be a bit less: 9-9.5 kWh at a guess,
>
> So a US gallon (3.78l) would be the equivalent of 37.8 kWh of
> unadulterated petrol or 34-36 kWh if its a gasoline/methanol blend.
>
> By comparison, the Gen 2 FES battery has 14 cells, each of 2.1 kWh, or
> 29.4 kWh for the standard 14 cell pack, so an hPh Shark (dual packs
> carried has just less than 60kWh of energy onboard, or 1.6 US gallons of
> avgas equivalent.
>
> The dual packs are about 18 litres total volume, so on a volumetric basis
> they're about 1/3 as good as petrol when it comes to storing energy in
> limited space.
>
>
-- 
Dan, 5J
September 30th 18, 01:38 AM
On Friday, September 28, 2018 at 9:58:43 AM UTC-6, Martin Gregorie wrote:
> On Fri, 28 Sep 2018 07:48:13 -0700, Soartech wrote:
> 
> >> Ultra capacitors !
> >   A gallon of gasoline contains 120 million Joules of energy.
> >
> A more useful equivalent for comparison is that a litre of petrol is  as 
> near as dammit 10 kWh in energy terms - and petrol spiked with methanol 
> will be a bit less: 9-9.5 kWh at a guess,
> 
> So a US gallon (3.78l) would be the equivalent of 37.8 kWh of 
> unadulterated petrol or 34-36 kWh if its a gasoline/methanol blend.
> 
> By comparison, the Gen 2 FES battery has 14 cells, each of 2.1 kWh, or 
> 29.4 kWh for the standard 14 cell pack, so an hPh Shark (dual packs 
> carried has just less than 60kWh of energy onboard, or 1.6 US gallons of 
> avgas equivalent. 
> 
> The dual packs are about 18 litres total volume, so on a volumetric basis 
> they're about 1/3 as good as petrol when it comes to storing energy in 
> limited space.
> 
> 
> -- 
> Martin    | martin at
> Gregorie  | gregorie dot org
But, an electric motor is more than three times as efficient as an internal combustion engine - 98% vs. 33% - so they don't need as much 'fuel'.
Martin Gregorie[_6_]
September 30th 18, 03:30 AM
On Sat, 29 Sep 2018 16:38:53 -0700, Bill.Daniels wrote:
> But, an electric motor is more than three times as efficient as an
> internal combustion engine - 98% vs. 33% - so they don't need as much
> 'fuel'.
>
Well, getting on that way - but certainly no better if you include the 
generation and charging efficiencies.
Actually, all I was looking to do was to put numbers to the overall 
efficiency of electric storage in terms of weight or volume compared with 
hydrocarbon fuels. Batteries are much worse here than petrol.
And there's another demerit too: run the tank dry on a turbo or jet and 
the empty tank is nice and light for the rest of the flight home, while a 
battery that has been run flat is no lighter than when it was fully 
charged.
A quick scan for zinc-air battery characteristics suggests they are only 
suitable for low power applications, tend to have a high self-discharge 
rate and don't like high temperatures or humidity. Nobody, that I found 
anyway, is quoting energy density (kWh/kg) or volumetric efficiency (kWh/
litre).
Bottom line: I like the idea of electric powered vehicles. But in this 
application the volume and weight of energy storage systems is all-
important, but electrochemistry is against any large improvement, at 
least for rechargeable batteries using currently proven chemistry. So far 
nobody has gotten better results from fuel-cells either, or we'd be 
seeing them in cars. 
-- 
Martin    | martin at
Gregorie  | gregorie dot org
2G
September 30th 18, 08:07 AM
On Saturday, September 29, 2018 at 6:30:20 PM UTC-7, Martin Gregorie wrote:
> On Sat, 29 Sep 2018 16:38:53 -0700, Bill.Daniels wrote:
> 
> > But, an electric motor is more than three times as efficient as an
> > internal combustion engine - 98% vs. 33% - so they don't need as much
> > 'fuel'.
> >
> Well, getting on that way - but certainly no better if you include the 
> generation and charging efficiencies.
> 
> Actually, all I was looking to do was to put numbers to the overall 
> efficiency of electric storage in terms of weight or volume compared with 
> hydrocarbon fuels. Batteries are much worse here than petrol.
> 
> And there's another demerit too: run the tank dry on a turbo or jet and 
> the empty tank is nice and light for the rest of the flight home, while a 
> battery that has been run flat is no lighter than when it was fully 
> charged.
> 
> A quick scan for zinc-air battery characteristics suggests they are only 
> suitable for low power applications, tend to have a high self-discharge 
> rate and don't like high temperatures or humidity. Nobody, that I found 
> anyway, is quoting energy density (kWh/kg) or volumetric efficiency (kWh/
> litre).
> 
> Bottom line: I like the idea of electric powered vehicles. But in this 
> application the volume and weight of energy storage systems is all-
> important, but electrochemistry is against any large improvement, at 
> least for rechargeable batteries using currently proven chemistry. So far 
> nobody has gotten better results from fuel-cells either, or we'd be 
> seeing them in cars. 
> 
> 
> -- 
> Martin    | martin at
> Gregorie  | gregorie dot org
Here is an interesting 2015 presentation on zinc-air batteries that indicates the possibility for very high energy densities (1200+ WHr/kg):
https://www.csm.ornl.gov/BLI8/presentations/J.%20CHO-UNIST-BYI8.pdf
Tom
Chris Wedgwood[_2_]
September 30th 18, 12:41 PM
On Friday, September 28, 2018 at 5:58:43 PM UTC+2, Martin Gregorie wrote:
> On Fri, 28 Sep 2018 07:48:13 -0700, Soartech wrote:
> 
> >> Ultra capacitors !
> >   A gallon of gasoline contains 120 million Joules of energy.
> >
> A more useful equivalent for comparison is that a litre of petrol is  as 
> near as dammit 10 kWh in energy terms - and petrol spiked with methanol 
> will be a bit less: 9-9.5 kWh at a guess,
> 
> So a US gallon (3.78l) would be the equivalent of 37.8 kWh of 
> unadulterated petrol or 34-36 kWh if its a gasoline/methanol blend.
> 
> By comparison, the Gen 2 FES battery has 14 cells, each of 2.1 kWh, or 
> 29.4 kWh for the standard 14 cell pack, so an hPh Shark (dual packs 
> carried has just less than 60kWh of energy onboard, or 1.6 US gallons of 
> avgas equivalent. 
> 
> The dual packs are about 18 litres total volume, so on a volumetric basis 
> they're about 1/3 as good as petrol when it comes to storing energy in 
> limited space.
> 
> 
> -- 
> Martin    | martin at
> Gregorie  | gregorie dot org
He did the Math..
Martin Gregorie[_6_]
September 30th 18, 01:23 PM
On Sat, 29 Sep 2018 23:07:27 -0700, 2G wrote:
> On Saturday, September 29, 2018 at 6:30:20 PM UTC-7, Martin Gregorie
> wrote:
>> On Sat, 29 Sep 2018 16:38:53 -0700, Bill.Daniels wrote:
>> 
>> > But, an electric motor is more than three times as efficient as an
>> > internal combustion engine - 98% vs. 33% - so they don't need as much
>> > 'fuel'.
>> >
>> Well, getting on that way - but certainly no better if you include the
>> generation and charging efficiencies.
>> 
>> Actually, all I was looking to do was to put numbers to the overall
>> efficiency of electric storage in terms of weight or volume compared
>> with hydrocarbon fuels. Batteries are much worse here than petrol.
>> 
>> And there's another demerit too: run the tank dry on a turbo or jet and
>> the empty tank is nice and light for the rest of the flight home, while
>> a battery that has been run flat is no lighter than when it was fully
>> charged.
>> 
>> A quick scan for zinc-air battery characteristics suggests they are
>> only suitable for low power applications, tend to have a high
>> self-discharge rate and don't like high temperatures or humidity.
>> Nobody, that I found anyway, is quoting energy density (kWh/kg) or
>> volumetric efficiency (kWh/
>> litre).
>> 
>> Bottom line: I like the idea of electric powered vehicles. But in this
>> application the volume and weight of energy storage systems is all-
>> important, but electrochemistry is against any large improvement, at
>> least for rechargeable batteries using currently proven chemistry. So
>> far nobody has gotten better results from fuel-cells either, or we'd be
>> seeing them in cars.
>> 
>> 
>> --
>> Martin    | martin at Gregorie  | gregorie dot org
> 
> Here is an interesting 2015 presentation on zinc-air batteries that
> indicates the possibility for very high energy densities (1200+ WHr/kg):
> https://www.csm.ornl.gov/BLI8/presentations/J.%20CHO-UNIST-BYI8.pdf
>
Interesting stuff but, unless I totally misunderstood the presentation: 
- the theoretical energy density of ZAB is around 170% of what LiFePO4
  can do (0.3 kWh/kg vs 0.18 kWh/kg). no comparison with Li-ion made.
  (page 4). 
- page 18 quotes a measured 1 kWh/kg. 
- page 32 quotes 0.0357 kWh/kg  (0.41 kWh/litre) for an experimental ZAB
  rig.
- page 36 quotes 1.9 kWh/kg (0.0036 kWh/litre) for a flexible cable
  format battery.
.... all quite a way short of the 10 kWh/litre (12.5 kWh/kg) of 
hydrocarbon energy storage.
The sort of high power performance needed for a car or aircraft motor 
wasn't really discussed or apparent in the accompanying numbers, charts 
and graphs.
  
Still, looks to be worth watching and the possibility of almost instant 
recharge by replacing the zinc becomes interesting if a cell with high 
power output can be designed for easy 'slip out/slip in' zinc replacement 
without needing special equipment, e.g to deal with the (highly alkaline) 
potassium hydroxide electrolyte. 
The possibility of recycling the 'used' zinc externally sounds good too.
  
-- 
Martin    | martin at
Gregorie  | gregorie dot org
2G
October 1st 18, 07:37 AM
On Sunday, September 30, 2018 at 4:23:22 AM UTC-7, Martin Gregorie wrote:
> On Sat, 29 Sep 2018 23:07:27 -0700, 2G wrote:
> 
> > On Saturday, September 29, 2018 at 6:30:20 PM UTC-7, Martin Gregorie
> > wrote:
> >> On Sat, 29 Sep 2018 16:38:53 -0700, Bill.Daniels wrote:
> >> 
> >> > But, an electric motor is more than three times as efficient as an
> >> > internal combustion engine - 98% vs. 33% - so they don't need as much
> >> > 'fuel'.
> >> >
> >> Well, getting on that way - but certainly no better if you include the
> >> generation and charging efficiencies.
> >> 
> >> Actually, all I was looking to do was to put numbers to the overall
> >> efficiency of electric storage in terms of weight or volume compared
> >> with hydrocarbon fuels. Batteries are much worse here than petrol.
> >> 
> >> And there's another demerit too: run the tank dry on a turbo or jet and
> >> the empty tank is nice and light for the rest of the flight home, while
> >> a battery that has been run flat is no lighter than when it was fully
> >> charged.
> >> 
> >> A quick scan for zinc-air battery characteristics suggests they are
> >> only suitable for low power applications, tend to have a high
> >> self-discharge rate and don't like high temperatures or humidity.
> >> Nobody, that I found anyway, is quoting energy density (kWh/kg) or
> >> volumetric efficiency (kWh/
> >> litre).
> >> 
> >> Bottom line: I like the idea of electric powered vehicles. But in this
> >> application the volume and weight of energy storage systems is all-
> >> important, but electrochemistry is against any large improvement, at
> >> least for rechargeable batteries using currently proven chemistry. So
> >> far nobody has gotten better results from fuel-cells either, or we'd be
> >> seeing them in cars.
> >> 
> >> 
> >> --
> >> Martin    | martin at Gregorie  | gregorie dot org
> > 
> > Here is an interesting 2015 presentation on zinc-air batteries that
> > indicates the possibility for very high energy densities (1200+ WHr/kg):
> > https://www.csm.ornl.gov/BLI8/presentations/J.%20CHO-UNIST-BYI8.pdf
> >
> Interesting stuff but, unless I totally misunderstood the presentation: 
> 
> - the theoretical energy density of ZAB is around 170% of what LiFePO4
>   can do (0.3 kWh/kg vs 0.18 kWh/kg). no comparison with Li-ion made.
>   (page 4). 
> 
> - page 18 quotes a measured 1 kWh/kg. 
> 
> - page 32 quotes 0.0357 kWh/kg  (0.41 kWh/litre) for an experimental ZAB
>   rig.
> 
> - page 36 quotes 1.9 kWh/kg (0.0036 kWh/litre) for a flexible cable
>   format battery.
> 
> ... all quite a way short of the 10 kWh/litre (12.5 kWh/kg) of 
> hydrocarbon energy storage.
> 
> The sort of high power performance needed for a car or aircraft motor 
> wasn't really discussed or apparent in the accompanying numbers, charts 
> and graphs.
>   
> Still, looks to be worth watching and the possibility of almost instant 
> recharge by replacing the zinc becomes interesting if a cell with high 
> power output can be designed for easy 'slip out/slip in' zinc replacement 
> without needing special equipment, e.g to deal with the (highly alkaline) 
> potassium hydroxide electrolyte. 
> 
> The possibility of recycling the 'used' zinc externally sounds good too.
>   
> 
> -- 
> Martin    | martin at
> Gregorie  | gregorie dot org
Here is an excellent paper that discusses the current state-of-the-art in zinc-air batteries:
https://www.researchgate.net/profile/Jing_Fu16/publication/311098275_Electrically_Rechargeable_Zinc-Air_Batteries_Progress_Challenges_and_Perspectives/links/59da6e38458515a5bc2b43b1/Electrically-Rechargeable-Zinc-Air-Batteries-Progress-Challenges-and-Perspectives.pdf
I haven't had time yet to read the full paper, but what I have read so far is most instructive.
Tom
Martin Gregorie[_6_]
October 1st 18, 12:47 PM
On Sun, 30 Sep 2018 22:37:42 -0700, 2G wrote:
> On Sunday, September 30, 2018 at 4:23:22 AM UTC-7, Martin Gregorie
> wrote:
>> On Sat, 29 Sep 2018 23:07:27 -0700, 2G wrote:
>> 
>> > On Saturday, September 29, 2018 at 6:30:20 PM UTC-7, Martin Gregorie
>> > wrote:
>> >> On Sat, 29 Sep 2018 16:38:53 -0700, Bill.Daniels wrote:
>> >> 
>> >> > But, an electric motor is more than three times as efficient as an
>> >> > internal combustion engine - 98% vs. 33% - so they don't need as
>> >> > much 'fuel'.
>> >> >
>> >> Well, getting on that way - but certainly no better if you include
>> >> the generation and charging efficiencies.
>> >> 
>> >> Actually, all I was looking to do was to put numbers to the overall
>> >> efficiency of electric storage in terms of weight or volume compared
>> >> with hydrocarbon fuels. Batteries are much worse here than petrol.
>> >> 
>> >> And there's another demerit too: run the tank dry on a turbo or jet
>> >> and the empty tank is nice and light for the rest of the flight
>> >> home, while a battery that has been run flat is no lighter than when
>> >> it was fully charged.
>> >> 
>> >> A quick scan for zinc-air battery characteristics suggests they are
>> >> only suitable for low power applications, tend to have a high
>> >> self-discharge rate and don't like high temperatures or humidity.
>> >> Nobody, that I found anyway, is quoting energy density (kWh/kg) or
>> >> volumetric efficiency (kWh/
>> >> litre).
>> >> 
>> >> Bottom line: I like the idea of electric powered vehicles. But in
>> >> this application the volume and weight of energy storage systems is
>> >> all- important, but electrochemistry is against any large
>> >> improvement, at least for rechargeable batteries using currently
>> >> proven chemistry. So far nobody has gotten better results from
>> >> fuel-cells either, or we'd be seeing them in cars.
>> >> 
>> >> 
>> >> --
>> >> Martin    | martin at Gregorie  | gregorie dot org
>> > 
>> > Here is an interesting 2015 presentation on zinc-air batteries that
>> > indicates the possibility for very high energy densities (1200+
>> > WHr/kg):
>> > https://www.csm.ornl.gov/BLI8/presentations/J.%20CHO-UNIST-BYI8.pdf
>> >
>> Interesting stuff but, unless I totally misunderstood the presentation:
>> 
>> - the theoretical energy density of ZAB is around 170% of what LiFePO4
>>   can do (0.3 kWh/kg vs 0.18 kWh/kg). no comparison with Li-ion made.
>>   (page 4).
>> 
>> - page 18 quotes a measured 1 kWh/kg.
>> 
>> - page 32 quotes 0.0357 kWh/kg  (0.41 kWh/litre) for an experimental
>> ZAB
>>   rig.
>> 
>> - page 36 quotes 1.9 kWh/kg (0.0036 kWh/litre) for a flexible cable
>>   format battery.
>> 
>> ... all quite a way short of the 10 kWh/litre (12.5 kWh/kg) of
>> hydrocarbon energy storage.
>> 
>> The sort of high power performance needed for a car or aircraft motor
>> wasn't really discussed or apparent in the accompanying numbers, charts
>> and graphs.
>>   
>> Still, looks to be worth watching and the possibility of almost instant
>> recharge by replacing the zinc becomes interesting if a cell with high
>> power output can be designed for easy 'slip out/slip in' zinc
>> replacement without needing special equipment, e.g to deal with the
>> (highly alkaline)
>> potassium hydroxide electrolyte.
>> 
>> The possibility of recycling the 'used' zinc externally sounds good
>> too.
>>   
>>   
>> --
>> Martin    | martin at Gregorie  | gregorie dot org
> 
> Here is an excellent paper that discusses the current state-of-the-art
> in zinc-air batteries:
> https://www.researchgate.net/profile/Jing_Fu16/publication/
311098275_Electrically_Rechargeable_Zinc-
Air_Batteries_Progress_Challenges_and_Perspectives/links/
59da6e38458515a5bc2b43b1/Electrically-Rechargeable-Zinc-Air-Batteries-
Progress-Challenges-and-Perspectives.pdf
> I haven't had time yet to read the full paper, but what I have read so
> far is most instructive.
> 
> Tom
Thanks for that. Saved for reading later.
-- 
Martin    | martin at
Gregorie  | gregorie dot org
krasw
October 1st 18, 01:22 PM
perjantai 28. syyskuuta 2018 18.58.43 UTC+3 Martin Gregorie kirjoitti:
> 
> By comparison, the Gen 2 FES battery has 14 cells, each of 2.1 kWh, or 
> 29.4 kWh for the standard 14 cell pack, so an hPh Shark (dual packs 
> carried has just less than 60kWh of energy onboard, or 1.6 US gallons of 
> avgas equivalent. 
I think FES battery has 14 cells at 41 Ah per cell. With 58 Volts you get the 2,1 kWh number (per battery back, and with some internal power loss). Two batteries and you end up 4,2 kWh of energy which gives you advertized hour flight duration with minimal power (4-5kW).
November 16th 18, 06:19 AM
One of the funny things with true metal air batteries is that they gain weight as they discharge (Zn => ZnO2), and surprisingly (cough) no promoter of the tech quotes Wh/kg for discharged batteries, which is what you'll be carrying around... they partially look so attractive because of that little cheat!
Dan Marotta
November 16th 18, 03:36 PM
Wow!Â* Looking at the atomic mass of each, that would be about a 50% 
increase (~65 for Zn and 16 or O) if all of the zinc was oxidized! Now 
I'm no chemist, that that looks HUGE to me!
On 11/15/2018 10:19 PM,  wrote:
> One of the funny things with true metal air batteries is that they gain weight as they discharge (Zn => ZnO2), and surprisingly (cough) no promoter of the tech quotes Wh/kg for discharged batteries, which is what you'll be carrying around... they partially look so attractive because of that little cheat!
-- 
Dan, 5J
Martin Gregorie[_6_]
November 16th 18, 03:54 PM
On Fri, 16 Nov 2018 07:36:18 -0700, Dan Marotta wrote:
> Wow!Â* Looking at the atomic mass of each, that would be about a 50%
> increase (~65 for Zn and 16 or O) if all of the zinc was oxidized! Now
> I'm no chemist, that that looks HUGE to me!
>
Yep - thats approximately a 25% weight increase. The zinc electrode will 
expand too: Zinc has a density of 7.14 vs 5.6 for ZnO, which implies 
something like a 28% volume increase if all the zinc in the battery of is 
oxidised when fully discharged. However, 100% oxidation is rather 
unlikely in any practical battery, and dealing with the volume increase 
means designing the case so it doesn't split when the battery is fully 
discharged.
-- 
Martin    | martin at
Gregorie  | gregorie dot org
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