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My adventures building a Zinc-Bromine battery
#31
Just was looking at a recent article along this line.

https://www.sciencedirect.com/science/ar...4220305356

Doesn't use a glass mat.
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#32
(10-07-2020, 01:39 AM)Bubba Wrote: Just was looking at a recent article along this line.

https://www.sciencedirect.com/science/ar...4220305356

Doesn't use a glass mat.

I have discussed that article extensively in my blog and studied it in great detail  Smile (see here for example https://chemisting.com/2020/09/12/zinc-b...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-woven fiberglass separator (https://tinyurl.com/y2ucz37x), which works quite well.
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#33
Just posted an article about the issues of TMPhABr solid layers plus what I have decided to try to solve this issue (https://chemisting.com/2020/10/08/zinc-b...he-answer/).
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#34
Very promising results using pre-soaked cathodes  Cool

These are some results using a CC4 cathode that was pre-soaked in 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:





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!
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#35
(10-09-2020, 04:24 PM)danielfp248 Wrote: 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
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#36
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.



Last CE=91.39% EE=68.81%

All charge/discharge curves plotted together:



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.
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#37
I want to share my latest post about some of the issues with the CC4 cathodes and the experiments that will follow (https://chemisting.com/2020/10/13/zinc-b...-above-80/)
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#38
So the GFE-1 cathode soaked in 10% TMPhABr and then air-dried before use, is a wonderful cathode. Given the significantly lower internal resistance I 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%). 



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 us in the territory of the commercial Zn-Br flow batteries in terms of energy storage characteristics  Big Grin
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#39
I have published a blog post showing what happened when I tried to push the energy density of the batteries above 40 Wh/L. I was able to achieve it, if only for a single cycle! Zinc dendrites got all the way to the cathode so I am trying an experiment with a different anode to figure this out. (https://chemisting.com/2020/10/17/zinc-b...d-40-wh-l/)
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#40
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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