My adventures building a Zinc-Iodine battery

danielfp248

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Sep 7, 2020
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For the first experiments I have been using Cu anodes (easily cut from copper tape), which have been easy to adhere to the Titanium electrodes and sand to reveal pristine copper. I also sanded down the Ti electrodes (320 and then 240 papers) before these experiments to ensure they are much more flat as they previously had some small irregularities due to the way in which they were cut.

The results so far have been really good, without any dendrites, when using a fiberglass separator. I was even able to run a cell for 141 cycles at 10mA/cm2 with a single layer of fiberglass separator with no issues (Exp 3b).

However, I am still experiencing substantial capacity decay. The fact that the decay is slower at higher current (10 mA/cm2 Vs 5 mA/cm2) (Exp 3a and 3b), suggest that the decay is related to some species that are generated and diffuse away from the electrodes. Since there is less time for diffusion at higher current, you expect diffusion related decay to be less prominent as electrode cycling becomes faster. This also matches the fact that Coulombic efficiency increased with current (97 at 10 mA/cm2 Vs 93 at 5mA/cm2).

I am now running an experiment (Exp 4) including 1M NaCl in the solution, to see the effect of further reduced water activity. After this is done I will run additional experiments at 2M NaCl and 5M NaCl, to see the effect this additive has on cycling characteristics.
 

danielfp248

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Exp12 is giving some really interesting results. It uses a copper anode, a Spectracarb 2050A-0850 Cathode, 3 layers of fiberglass separator and an electrolyte made of 15m ZnCl2 + 5m KI + 1m NaCl in distilled water. I am testing this at a current density of 10mA/cm2, charging to 1.45V and discharging to 0.5V.

So far the battery has cycled exactly 100 times. This is the first time potential and capacity changes have seemingly stabilized. Coulombic efficiency is also now consistently in the >97% region. No dendrites have appeared yet either.

1637686962570.png
The graphs below show the changes in capacity and changes in potential as functions of cycle number:

1637687013676.png
1637687127138.png

Capacity is at around 1.07mAh, given the volume of the battery of 0.1032cm^3 and an average discharge potential of 1.03V, the energy density of this battery is at 10.88 Wh/L. The most exciting aspect of this battery is its stability so far, which I hadn't been able to achieve before. I'm going to run it until it decays to 20% of max capacity, dies due to dendrites or reaches 2000 cycles🤞.
 

danielfp248

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The battery ran for 222 cycles. Decay became significantly more pronounced during the last 30 and the stability in the potentials was only temporary, there were also some small dendrite issues. So far this is the battery I have cycled for the longest yet.

1637753152280.png
 

Andrew Cote

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Nov 16, 2021
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Hello Daniel,

I have an interesting design and application for a titanium dioxide-based battery. Do you make and test batteries as a hobby or is it your business?
 

danielfp248

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Hello Daniel,

I have an interesting design and application for a titanium dioxide-based battery. Do you make and test batteries as a hobby or is it your business?

I do it as a hobby, I have no plans or goals to ever make any of this commercial. It is just to learn and share with anyone interested.
 

danielfp248

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This is Exp21, using CCP cathode, 3 layers of fiberglass separator, copper anode and the regular ZnCl2 15m + KI 5m electrolyte. This cell is being cycled between 0.8V and 1.275V at 10mA/cm2. So far 100 cycles and the battery capacity went down and then back up close to max capacity.

1638131294301.png

I decided to cycle only to 0.8V because the copper anode seemed to face some deterioration when cycling down to 0.5V. The current capacity of this battery is on the lower side - energy density is around 4Wh/L - I want to see for how long it lasts under these conditions. Mean charge potential seems to be stable for now. Coulombic efficiency is in the 96-97% range, energy efficiency is in the 82-83% range.

Will this battery finally be long term stable?
 

danielfp248

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I am now repeating Exp12 - the longest lasting yet at 222 cycles - but using a Zn anode instead of a Cu anode to see what effect this has. All other variables are exactly the same.

So these results were still very similar, an increase of capacity up until a maximum, then a linear decline of capacity that doesn't stop. Even with CE values above 98% this decay doesn't cease to exit. Something forms that causes these Zn-I batteries to decay and die with time, sadly I don't have the tools to figure out exactly what it is.

Given that it happens with a variety of anodes and cathodes, it is likely related with some impurity in the solution or with some aspect of the chemistry at high current densities that wasn't addressed on the paper I used as a basis for these batteries.

Because of this road block I might need to change the chemistry I study, yet again.

So far I have yet to see a chemistry that is stable enough, both Zn-I and Zn-Br suffer from very big problems in terms of side-reactions that damage the electrodes or the electrolyte and cause big capacity or efficiency losses as a function of time.

I might try someone's previous suggestion to study the Zn-MnO4 chemistry, which is pretty benign to work with at home.
 

danielfp248

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I invite you to follow my new thread on Zn-MnO4 batteries


This doesn't mean I won't continue doing Zn-I experiments at some point.
 

Juptron

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Nov 2, 2020
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I invite you to follow my new thread on Zn-MnO4 batteries


This doesn't mean I won't continue doing Zn-I experiments at some point.
Thanks for sharing, and good luck with the new experiment, also Sodium ion battery looks like a worthy candidate....
 

danielfp248

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Sep 7, 2020
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Thanks for sharing, and good luck with the new experiment, also Sodium ion battery looks like a worthy candidate....

Sadly Sodium ion batteries require inert conditions for assembly (no water or oxygen) so I cannot do that at home.
 
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