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diy solar

My adventures building a Zinc-Iodine battery

The battery in #19 did not last too long under these conditions, with evident mounting damage as a function of time. With the low CE (<60%) a lot of side reactions were likely happening in the battery which led to strong capacity loss as a function of cycle number. This battery has been a significant breakthrough as I had never been able to achieve a capacity this high with a ZnI2 battery.

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I will be trying several new ideas this week. Stay tuned!
 
The first WiS (water-in-salt) battery I constructed dried due to some air openings in my Swagelok cell. I added teflon tape to the electrodes to provide a tight seal and prevent contact with the outside environment. I then made a second WiS Zn-I device per the description in the post linked in #24. This is the first cycle:

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The device was charged to 1.35V and discharged to 0.6V at a current of 5mA (3.87mA/cm2). This first cycle showed a CE of 88% with an EE of 78%. The measured capacity is 2.23mA/h, given the dimensions of the device, this gives an energy density of 62 Wh/L. I will keep cycling it and post some more results.

This is the best device I have ever built! ?
 
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After 4 cycles, the battery had a big voltage drop and seems to have failed. After opening it up, it seems the Whatman filter paper reacted with the Iodine or most of the iodine got deposited in it instead of the carbon cloth. I took a picture for you guys.

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HB-1070 cathode on the left, Whatman 42 filter paper separator to the right. I decided to change back to Fiberglass to see if I could solve this stability issue. This adds 200um to the battery, making the total thickness around 550um. This is because the fiberglass I have is very porous, so I need at least 4 layers (at 100um each), to avoid shorting.

It is also worth noting that I am charging/discharging at around 10x the current level of the paper where I took this idea from, where they cycle the battery at around 300uA/cm2.
 
First cycle of the glass separator WiS battery. I used four layers of fiberglass separator and an HB-1070 cathode. Charged to 1.35V, discharged to 0.5V at 5mA. CE = 87.9%, EE = 80.73%, Thickness = 0.055cm, Diameter = 1.29cm2, Energy Density = 30.43Wh/L, Mean Discharge Potential = 1.27V.

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First five cycles of the battery first tested in #31:

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So far, there is some loss in initial capacity, which matches the WiS paper results. If my results continue to match, we should see a decrease in capacity for the first ~50 cycles, followed by an increase in capacity for the following 100+ cycles. Last cycle CE and EE values remain very high.
 
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The battery from #31 experienced failure after 7 cycles, from what seems to be a dendrite related problem. It might be that this WiS approach leads to dendrites at these higher current levels compared to those in the paper. However, I also realized that my fiberglass was failing because I was tightening the Swagelok cell too much upon closure, which squished the fiberglass into the cathode and caused shorting unless I used 4 layers. This also likely made dendrites much worse as it compacted the electrodes together too much.

I now built a WiS device using a CC6P cathode (350um) with only 2 layers of fiberglass separator (260um each)(total thickness of 870um). Taking care not to tighten beyond just contact of the electrodes. I did not get any shorting at all, despite only using 2 fiberglass layers. This test uses my thickest carbon cloth material and less fiberglass. I am going to cycle at 5mA from 0.5-1.35V and see if I get the same failure mode.
 
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Also note I decided to charge the battery described in #33 to 1.3V instead of 1.35V, since upon starting the first charging cycle I noticed that the CC6P cathode has greatly increased the capacity.
 
The CC6P cathode really changed the dynamics of the battery. This carbon cloth is significantly thicker, at 350um, and the total cell thickness is now larger at 870um. However, the internal resistance of the battery is also significantly lower and the potential increases much more slowly, so I was able to increase the current to 15mA (11.6mA/cm2) and only charge the battery to 1.3V. There is no exponential runup at the end, which means that I'm probably under-charging the battery. However, I want to test how many cycles I can get before damage under these conditions. The first cycle is shown below:

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CE = 92.90%, EE=77.96%, MeanV=1.17V, Capacity = 2.51mAh, Energy Density = 26.17Wh/L.

I'll post more graphs as the testing progresses!
 
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Plating battery electrodes in the WIS seem to be a good way to produce an cathode filled with I2 instead of using ovens or vacuum chambers,but doesn't show a good result in cycling stability for now.
If the I2 is successfully confined in a nanoporous carbon cloth substrate,you may go back the previous paper A sustainable aqueous Zn-I2 battery which show a great cycling stability.Use the cathode produced in the WIS and then switch the electrolyte and battery structure to the paper one.
After all, solving the stability problem is where it all starts.
That's just my little suggestion.
 
Plating battery electrodes in the WIS seem to be a good way to produce an cathode filled with I2 instead of using ovens or vacuum chambers,but doesn't show a good result in cycling stability for now.
If the I2 is successfully confined in a nanoporous carbon cloth substrate,you may go back the previous paper A sustainable aqueous Zn-I2 battery which show a great cycling stability.Use the cathode produced in the WIS and then switch the electrolyte and battery structure to the paper one.
After all, solving the stability problem is where it all starts.
That's just my little suggestion.
It is an interesting idea, to make the iodine electrode electrochemically in WiS and then swap it. I'll leave it as a possibility for a future test.
 
After 53 cycles charging to 1.3V and discharging to 0.5V at 15mA (battery made in #36), the battery capacity has dropped to around 40% of initial capacity. The CE and EE remain very high at 95% and 80% on the last cycle. In accordance with the paper, we have now observed a drop of 50-60% of capacity during the first 50 cycles of the battery, question is if we'll observe the aggressive capacity recovery and surpassing that they saw when running the battery an additional 300 cycles.

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In any case, the battery has now avoided death, so it seems battery death was indeed caused by excessive pressure when closing the Swagelok cell.

I will keep cycling the battery to see what we get ?
 
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