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My adventures building a Zinc-Bromine battery

I cycled 25 times to 15mAh, no problems at all:

1604021873722.png
I have decided to stop cycling at this point and run a "max capacity" experiment. I am going to charge the battery to 2.1V, see how much charge I am able to store and how much I can recover, test the limits of the battery's energy density.
 
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So I ran a cycle until the battery reached 2.1V at 15mA, discharging at this same current to 0.5V. The battery had a CE=78.57% with an EE=58.59%. Total charge I was was able to extract was 26.56mAh, which would give the battery a capacity of 62Wh/L. However the battery failed during the second cycle - classic dendrite related failure - so charging to this capacity is not going to be viable. The injected charge was 33.78mAh, so if this is the max capacity, 75% of this value would be around 25mAh, which is 10mAh higher than what I've been charging the battery to. For the following experiments I will be charging to this capacity instead.

1604065632232.png

I have now put together a new battery with the same configuration, will charge/discharge to 25mAh at 15mA. We'll see what we get :)
 
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First curve is done, the battery behaved very well on first charge/discharge. CE =85.86% EE = 68.22% ?. Total charge recovered was 21.13 mAh, energy density is at ~45Wh/L. For battery configuration see #122

1604078422951.png
 
I've been thinking about starting an Instagram account to share pictures and stories about the fabrication of these devices and my experiments. Do you guys think this would be interesting for you? Let me know :)
 
danielfp248 said:
I've been thinking about starting an Instagram account to share pictures and stories about the fabrication of these devices and my experiments. Do you guys think this would be interesting for you? Let me know :)
Click to expand...
Would be cool too, I love the blog post and your post here it's more detailed, having to see more pictures on Instagram would be very fine as well...
 
danielfp248 said:
I've been thinking about starting an Instagram account to share pictures and stories about the fabrication of these devices and my experiments. Do you guys think this would be interesting for you? Let me know :)
Click to expand...
Hi Daniel.

The more the better! I still owe you some pictures and discharge curves of my setup.

I think your carbon felt is really making the difference. I have graphite felt which doesn't seem to have a very large surface area. The results with TPABr are very poor unless I coat the felt with activated carbon (nitrocellulose binder). I still haven't managed to get anywhere near my 34 Wh/L I can get without a sequestering agent, so your results are truly impressive!

I also think TMPhA Br is a better sequestering agent than TPA Br. I say that simply based on TMPhA being more polar and clearly sequestering (as you have shown).

I have done some reading and I can activate my felt with simple heating or chemical treatment in permanganate, but I don't see anything with a surface area like 1000 m^2 like your felt.

I would eventually like to make the electrode myself. Let's see how that goes.
 
I started having some weird stability issues with devices in the separator-less setup ☹️ Trying to figure out what's going on. Here is a pretty plot showing what I'm experiencing:

1604444087064.png
 
According to Rob on YouTube, this design doesn't or shouldn't have much issues with dendrites problems, please if you have the time and resources do take a look this too
 
Juptron said:
According to Rob on YouTube, this design doesn't or shouldn't have much issues with dendrites problems, please if you have the time and resources do take a look this too
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Thanks for your comment! The problem with this design is that the internal resistance is so high - due to the distance between electrodes - that the energy efficiency will be abysmal (probably lower than 10%). Putting 10 Wh in to get 1Wh out is not practical unless you have a lot of energy to waste. In practice if you want to get high energy efficiencies (>50%) you will need to keep your electrode distance below 5mm. This is because of limits in the conductivity of Zinc Bromide solutions. This is why these "jar batteries" are not practical Zn-Br batteries. Note that their Coulombic efficiency can still be quite high (>80%) but this does not mean the battery is any good in real terms.

With electrode distances so short, zinc dendrites are sadly going to be a problem we will have to solve.
 
danielfp248 said:
Thanks for your comment! The problem with this design is that the internal resistance is so high - due to the distance between electrodes - that the energy efficiency will be abysmal (probably lower than 10%). Putting 10 Wh in to get 1Wh out is not practical unless you have a lot of energy to waste. In practice if you want to get high energy efficiencies (>50%) you will need to keep your electrode distance below 5mm. This is because of limits in the conductivity of Zinc Bromide solutions. This is why these "jar batteries" are not practical Zn-Br batteries. Note that their Coulombic efficiency can still be quite high (>80%) but this does not mean the battery is any good in real terms.

With electrode distances so short, zinc dendrites are sadly going to be a problem we will have to solve.
Click to expand...
Thanks for the information, Just that this is one of the most diyest... Battery I have ever come across hence my fascination for it ?. ... Thanks for what you are also doing! I see this https://www.sciencedirect.com/science/article/pii/S2589004220305356 is helpful for your current work too...
 
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Juptron said:
Thanks for the information, Just that this is one of the most diyest... Battery I have ever come across hence my fascination for it ?. ... Thanks for what you are also doing! I see this https://www.sciencedirect.com/science/article/pii/S2589004220305356 is helpful for your current work too...
Click to expand...

Thanks for your reply! I discuss that paper extensively on my blog. Note that their capacity, energy density and specific power numbers are incredibly misleading, since they are calculated without considering the mass of the electrolyte or total mass of the cathode (for the capacity) or the total mass of the cathode and water in the electrolyte (for the density and specific power). When you consider these factors their values drop by around 100x which matches what we know about commercial Zn-Br technology. If these numbers actually held, this paper would have been published in Nature or another top tier journal :)
 
danielfp248 said:
Thanks for your reply! I discuss that paper extensively on my blog. Note that their capacity, energy density and specific power numbers are incredibly misleading, since they are calculated without considering the mass of the electrolyte or total mass of the cathode (for the capacity) or the total mass of the cathode and water in the electrolyte (for the density and specific power). When you consider these factors their values drop by around 100x which matches what we know about commercial Zn-Br technology. If these numbers actually held, this paper would have been published in Nature or another top tier journal :)
Click to expand...
Ok, but anything practically from 30wh/l looks good to me ?
 
After 20 cycles, the battery is still going strong. Energy efficiency has decreased slightly, but Coulombic efficiency remains above 92%. No sign of dendrites yet :) I will continue cycling, see how long it takes for the battery to fail!

1605364103218.png
 
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