My adventures building a Zinc-Bromine battery

danielfp248

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vspin said:
Wish there was a live data feed. :)This is exciting stuff.

My fingers are crossed..

Thanks for following my progress :D

The battery did 100 cycles without an issue (charging/discharging at 2mA). CE and EE evolution is shown below.Final values were CE=89.79%, EE=73.68%.


image_xetesa.jpg


I have now stopped that test and will be doing another test running it at more than double the current density (5 mA). We'll see if it can handle that! :cool:
 

vspin

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danielfp248

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I did some initial experiments that didn't have great results because dendrites started forming at around cycle 5, I was also having issues with increased series resistance in the battery due to the fact that the electrolyte contained some solid TMPhABr that I didn't filter and that got deposited on top of the cathode when I put the cell together (forming an low-conductivity layer between the cathode and the graphite electrode of the Swagelok cell).

I then decided to add 1% PEG to the electrolyte to reduce Zn dendrite formation, filter the saturated electrolyte and make sure to allow for a few minutes of soaking of all the fiberglass layers and the carbon cathode before putting together the cell. The cell does contain 50mg of TMPhABr as a layer between the cathode and the first fiberglass layer.

These are the results up until now, charging/discharging at 2mA to 2000 uAh (4x more specific energy than before!)



image_kygwkn.jpg


Last cycle has a CE=88.93% with an EE=71.04%.


image_yzbbem.jpg


I am going to cycle this cell for another 100 cycles (will probably take a week!) see how it evolves. I believe this is a big step, since I was able to dramatically increase the specific energy of the device:cool:
 

100kwh-hunter

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I dont know the amount of gold/funds or excess to materials you have...meaning by this i assume/presume you can get the material nearly for free?
But i would like to tribute something for your materials, if needed, it wont be much...but 10 is 10, right?
What if more forum members think this way?
So if the need arises you can do more...., i will jump in when i think it is the time to experimentwith my pre historic whatever...
(-:...oke 70% of my thought is industrial....I must be honest...
I am FULLY AWARE that billion dollar companies invest a lot in znbr and did not succeed..........

But what if wemanagein hobby scale ......and in the end....like always the industry takes it all....
Just that hobby scale, a workable hobby scale, some techiethingie from 1880....

Btw i printed some ofyour work to do some side rechercheand sideinvestigation....
Nice write ups.
 

danielfp248

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Aug 31, 2020
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100kwh-hunter said:
I dont know the amount of gold/funds or excess to materials you have...meaning by this i assume/presume you can get the material nearly for free?
But i would like to tribute something for your materials, if needed, it wont be much...but 10 is 10, right?
What if more forum members think this way?
So if the need arises you can do more...., i will jump in when i think it is the time to experimentwith my pre historic whatever...
(-:...oke 70% of my thought is industrial....I must be honest...
I am FULLY AWARE that billion dollar companies invest a lot in znbr and did not succeed..........

But what if wemanagein hobby scale ......and in the end....like always the industry takes it all....
Just that hobby scale, a workable hobby scale, some techiethingie from 1880....

Btw i printed some ofyour work to do some side rechercheand sideinvestigation....
Nice write ups.

I fully fund all my homeresearch myself - don't have the luxury of having access to high-end research labs at the moment. It hasn't been outrageouslyexpensive though - I have probably spent less than 1K USD at the moment - since the scale I work in is really small, so I can do a lot of prototyping without spending a lot of money on materials. I honestly have bought more things than I have used - I bought a lot of sample cathode materials that I haven't even tested yet - so there's still a bunch of research to do without having to spend more money.

Thanks for your offer of donating!I will certainly consider that if the need for additional resources does arise :) .

I also see this as a hobby, just a problem I want to understand a little bit better and - hopefully - make some useful contribution to. I have good contacts in research labs so I might choose to publish some of this research if I make some good findings and I can find some friends to expand on them or maybe I'll have the time to work at a lab for a while and get it done at a higher level. Right now my desire is just to personally understand and improve things at a small scale :D
 

danielfp248

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Bubba said:
Just was looking at a recent article along this line.

https://www.sciencedirect.com/science/article/pii/S2589004220305356

Doesn't use a glass mat.

I have discussed that article extensively in my blog and studied it in great detail :) (see here for examplehttps://chemisting.com/2020/09/12/zinc-bromine-batteries-can-they-really-be-that-good/). Note that a lot of the numbers they arrive at on the article are unrealistic. The charge/discharge capacities are calculated using only the amount of active carbon material in the cathode (3mg) and the specific energy and power are calculated using only the mass of the cathode active material plus zinc bromide and TPABr (completely ignoring water, which is most of the mass of the electrolyte in their case).

Also, I don't use a glass matt! I use a non-wovenfiberglass separator (https://tinyurl.com/y2ucz37x), which works quite well.
 

danielfp248

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Very promising results using pre-soaked cathodes :cool:

These are some results using a CC4 cathode that waspre-soakedin TMPhABr 50% solution, then air-dried before use. This is using a 3M ZnBr2 solution containing 10% PEG-200, charge/discharged at 2mA, charged to 3000 uAh, discharged to 0.5V:


image_tngyol.jpg



image_trukhe.jpg


I'm going to cycle this till it fails or till the EE drops below 60%.

After this there are several experiments to run:

  • TMPhABr loadings (using 5%, 10%, 25% solutions)
  • Carbon cathodes (I have 4 different types of carbon cloth, 2 types of felts and 2 types of papers)
  • PEG-200 concentrations (10%, 15%, 20%)
It will take a while but, with the CE and EE figures now above 80% and 60% respectively, it does seem we should be able to achieve a viable static ZnBr2 battery!
 

100kwh-hunter

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Mar 2, 2019
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698
danielfp248 said:
Very promising results using pre-soaked cathodes :cool:
it does seem we should be able to achieve a viable static ZnBr2 battery!

I really hope your efforts are going to pay off now.
Thanks again for posting so much info.
I cant wait to see some good results.

With best regards and again good luck, Igor
 

danielfp248

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Aug 31, 2020
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Latest test uses a 3M ZnBr2 + 10% PEG200 solution with a CC4 cathode that was soaked in 50% TMPhABr and then dried in air. This cell was cycled 43 times at a current of 5mA, charged to 3000 uAh and discharged to 0.5V.


image_udzldd.jpg


Last CE=91.39% EE=68.81%

All charge/discharge curves plotted together:


image_nbpptp.jpg


These battery was very stable, with no formation of Zn dendrites and no substantial drops in CE or EE through the entire experiment. I am now cycling it at 10mA to see how the CE and EE change at a higher current density.

Following this test I will be performing experiments with CC4 cathodes soaked in a 10% TMPhABr solution, to see how the results change at a siginficantly lower concentration of TMPhABr in the cathode.


Internal resistance was too high to cycle at 10mA, so I opened the battery up and will now continue with the next experiment.
 

danielfp248

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So the GFE-1 cathodesoaked in 10% TMPhABr and then air-dried before use, is a wonderful cathode. Given the significantly lower internal resistanceI was able to increase the current density to 10mA and increase the capacity to 5000 uAh while retaining - so far -high CE and EE values (CE=87.45% EE=76.11%).


image_yvxnbk.jpg


This puts the specific energy of the battery at 50-55Wh/kg. I will keep cycling it to see how stable it is!

But this is exciting, it's putting usin the territory of the commercial Zn-Br flow batteries in terms of energy storage characteristics :D
 

danielfp248

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I ordered some Sodium Bromide and Zinc Sulfate in order to test an electrolyte comprised of Zinc Bromide, saturated with Sodium Sulfate plus 20% PEG-200. Sodium sulfate is known to reduce the edge formation of Zinc dendrites (see here)so this seems like a nice experiment to test a much cheaper electrolyte that can also help with the formation of dendrites. The electrolyte is much cheaper because both NaBr and ZnSO4 are available in kilogram quantities for low amounts of money (compared to Zinc bromide, which is much more expensive at small scales).

In order to prepare the electrolyte I plan to prepare a solution with 6M NaBr + 3M ZnSO4 + 20% PEG-200, this will give me the 3M ZnBr2 I need but will be above the solubility limit of NaSO4 at ambient temperature, so I will filter out the solution to remove the precipitated NaSO4. This should serve to reduce the series resistance of the cell and hopefully the dendrites as well. These are experiments for next week though, in the meantime I'll keep on testing my current electrolytes made of 3M ZnBr2.
 
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