My adventures building a Zinc-Iodine battery

For these tests, I built a battery using the 15m ZnCl2, 5m KI, 5m NaCl WiS electrolyte using a CC6P cathode and two layers of fiberglass. I decided to charge the battery to just 1mAh of fixed charge capacity, at 10mA. This is in order to test cycling stability quickly as I have always been getting degradation as a function of cycle number, even at lower capacities.




I am very excited to say that after 10 cycles, the capacity has been steady and the charge/discharge voltages have actually improved as a function of time. The coulombic and energy efficiency values did decrease a little bit compared to previous experiments without NaCl in the WiS electrolyte, but stability has increased tremendously. I am going to cycle 50 times to this capacity, if stability remains good, I will proceed to cycle at higher capacities (4mAh) and see what we get ?

I cycled the device 21 times, charging to 1mAh, discharging to 0.5V, at 10mA, the results show it is very stable , even gaining capacity up until the last cycle. Moreover, it is improving significantly on CE and EE values (final values are CE=91.12%, EE=74.91%). I have now stopped the test and started testing to 4mAh at 10mA. Let's see if it is still stable up to higher capacity!




Note, there are no published results of devices with this exact electrolyte. These are completely new research results ?

I ran one single cycle but it had some issues, gave CE>100 and discharge capacity > 4mAh, even though I had charged it to 4mAh. The battery probably had some charge remaining from the previous short cycles that ran to 1mAh. I shorted the battery for 5 min to completely discharge it and started the test again. Charging to 4mAh at 10mA.

First 5 cycles to 4mAh, for the battery built in #51:




As you can see, up until now we have great cycling stability, with increasing capacity for the first 5 cycles and increasing CE and EE values. This behavior matches the results that we got when charging to only 1mAh. Maximum energy density at this moment is 35.35Wh/L. This is in great contrast to previous test using the original WiS electrolyte from the paper, where at this point our capacity had already dropped drastically. The modified WiS electrolyte seems to be paying off ?

Right after I posted the above, the battery died as a cause of a short. It does seem 10mA is too high of a current for this electrolyte. I just built another battery with the same electrolyte and will try charging/discharging at only 5mA to 4mAh. Results will take significantly longer, so I'll post them probably next weekend.

Also worth noting that I saw absolutely no evident dendrites when I opened up the battery, Zinc plating seemed quite homogeneous and the separator had no grey marks, which are evident when dendrites grow through it. It might be that the plating got thick enough to contact a stranded conductive carbon fiber. The CC6P cathode has a lot of fibers (especially around the places where the circle is punched from the cloth) and it is easy for one of those to be within easy rich with just two layers of fiberglass separator.

The next battery is therefore going to be a CC4P carbon electrode (which is thinner at 250 microns and is cut more cleanly), with 3 separator layers instead of just 2.

Amazing research!

Very impressive coulombic efficiency measures.
This thread is helping me learn about fundamental physics a bit as I attempt to follow and read along. Thank you!

A random query: do you have any thoughts on the topic of transducer based agitation of cells being studied with relationship to the chemistry dynamics of the cell? e.g. piezo or otherwise. i suppose this sort of approach is maybe pointless because how could a large pack vibrate. something about crystals being broken up or scattered by random motion. kind of like shaking a box of ping pong balls to pack them better. although packing better might cause more resistance evolution. anyways digressing!

Just kind of randomly wondered. Sorry if it’s OT.

I also wanted to point your attention to one of the previous results. When I forced charging to 3mAh on a battery with the original ZnCl2+KI electrolyte (#45).


Notice how in cycles where the charging potential went very high - above 1.6V - we actually got some discharge at the 1.6V level. This points to the formation of some I+ in the cell that, at least for a little bit, was reversibly discharged. Recent research shows that it is possible to have this process in a WiS ZnCl2 electrolyte (see here) although they used LiCl2 and Acetonitrile to achieve good stability and reversibility. In 30m ZnCl2, the process wasn't very stable.

If I achieve good stability in the current test using a CC4P cathode with the new ZnCl2+KI+NaCl electrolyte, I wonder if I might be able to achieve the 4 electron process and charge to 1.8V. Since this electrolyte has much lower water activity it should in fact lead to much more stable I+ formation. Sadly, the authors of the nature paper mentioned above didn't do any ZnCl2+LiCl tests in the absence of acetonitrile, so no one seems to have tested something close.

curiouscarbon said:

Amazing research!

Very impressive coulombic efficiency measures.
This thread is helping me learn about fundamental physics a bit as I attempt to follow and read along. Thank you!

A random query: do you have any thoughts on the topic of transducer based agitation of cells being studied with relationship to the chemistry dynamics of the cell? e.g. piezo or otherwise. i suppose this sort of approach is maybe pointless because how could a large pack vibrate. something about crystals being broken up or scattered by random motion. kind of like shaking a box of ping pong balls to pack them better. although packing better might cause more resistance evolution. anyways digressing!

Just kind of randomly wondered. Sorry if it’s OT.

Click to expand...

Thanks for your reply and likes! I'm glad you like to follow my progress.

About your "random query", sadly I am unfamiliar with the topic you mention, so I cannot help answer your question.

Thanks!

Very productive work going on here, thanks for sharing!

I've been trying to increase the cycling stability of the batteries, as most of the batteries I made were either dying due to shorts after 5-10 cycles or their capacity was fading quickly after the first 10-20 cycles.

I tested a battery using a CCP cathode (150um) with a Whatman 42 filter (200um) paper as separator and a Zinc anode. The electrolyte is made from 15m ZnCl2 + 5m KI + 5m NaCl in white vinegar (4% v/v Acetic acid). The idea of the white vinegar is to increase ion mobility, since the dipole moment of acetic acid is larger than that of water. Note that the electrolyte itself is already very acidic (pH < 2), so the acetic acid is all protonated under these conditions and merely provides a higher dipole moment media.

I wanted to test stability. This means reaching a higher cycle number quickly, for this reason, the battery was charged to 1.3V at 10mA, discharging to 0.5V. Previous attempts had shown poor results under these conditions. The results up until now are below (first 100 cycles):



The CE is stable and mostly above 98% and the EE is above 80%. So far capacity has been quite stable, although it is clear that some instability still remains. Since the battery is being charged to a low potential at a relative high current density (7.75mA/cm2), the energy density is quite low, currently at around 9.66Wh/L. I want to be able to reach a cell that is stable for >500 cycles before I aim for higher capacity, as higher capacity and densities are meaningless if a cell is simply unstable.

The achievement of a CE > 98% is already a significant improvement from the original paper. Both the use of vinegar and the use of a Zn metal anode (instead of the graphite anode of the Swagelok cell) have been critical in the improvement of the battery.

wow, the capacity fade is significantly less than in previous experiment trials!

and very uniformly high CE and extremely stable EE!

thank you for sharing! ?

I stopped the battery after 138 cycles, when it started showing accelerated capacity loss. I also fixed a small error in my EE calculation, so the average EE is actually around 78%, not 80%.

I just assembled a battery using a CCP cathode, a Whatman 42 filter separator, a zinc anode and an electrolyte using 19m ZnCl2 + 5m KI in white vinegar. I want to see the effect of a higher ZnCl2 concentration, as I am probably using a lower purity ZnCl2 compared to that used in the article. I will be charging to 1.3V at 5mA, discharging to 0.5V.

curiouscarbon said:

wow, the capacity fade is significantly less than in previous experiment trials!

and very uniformly high CE and extremely stable EE!

thank you for sharing! ?

Click to expand...

Thanks a lot for your support! Messages like this mean a lot to me. Very happy to share

danielfp248 said:

I just assembled a battery using a CCP cathode, a Whatman 42 filter separator, a zinc anode and an electrolyte using 19m ZnCl2 + 5m KI in white vinegar. I want to see the effect of a higher ZnCl2 concentration, as I am probably using a lower purity ZnCl2 compared to that used in the article. I will be charging to 1.3V at 5mA, discharging to 0.5V.

Click to expand...

This cell charged to much higher capacity (1.2mAh) but died due to a short - probably caused by dendrites - after 3 cycles. It seems devices with higher capacity die due to dendrites when using a 200um Whatman 42 separator quiet quickly, the formation of dendrites is the most likely culprit. Makes me think if this is one of the main reasons why the paper never charged at currents this high. No mention of dendrites is ever made in the paper.

I am now testing a cell on a 22m ZnCl2 + 5m KI + 5m NaCl electrolyte in distilled water (CCP cathode, W42 separator, zinc anode), charging to 1.4V at 5mA. Charging to 1.4V will make dendrites appear faster if they are indeed present. This electrolyte has dramatically lower water activity which should also lead to significantly lower dendrite formation. We'll see if that's actually the case.

Increasing the ZnCl2 increases the electrical resistance a lot, without preventing the shorting that happens. The battery made with 22m ZnCl2 died after a few cycles. Increasing ZnCl2 to 30m gave even worse results as virtually all cell capacity is lost due to the huge increase in resistance (as reported in the paper).

I have never ran a test of the ZnCl2 15m + KI 5m in distilled water with a Zn anode, so I will be running that (which will be the exact same setup of the paper) to see if I still get the shorting problem. I will charge to 1.3V and discharge to 0.5V at 5mA.

These are the results for a cell with ZnCl2 15m + KI 5m in distilled water, CCP cathode, Zn anode, W42 separator. Charged to 1.3V, discharged to 0.5V at 5mA. I ran it for 6 cycles without any shorting appearing. The lower ZnCl2 concentration allows for much better ion mobility, which means the capacity increases significantly. This cell had a max energy density of 31.7Wh/L at this current density.


I then constructed the same cell, but using a vinegar as the solvent, which is running now.

It is also worth noting that the original WiS article did not use carbon cloth, but a carbon fiber paper. I have bought some additional carbon materials to test:


These were all bought from fuelcellearth.com. I will therefore have 4 cloths, 1 felt and 4 carbon fiber papers to test this chemistry on.

These are the results for a cell with ZnCl2 15m + KI 5m in vinegar, CCP cathode, Zn anode, W42 separator. Charged to 1.3V, discharged to 0.5V at 5mA. I ran the battery for 39 cycles, when decay became too pronounced.



Also, got the carbon papers today! So I will be doing a test with an MGL280 paper next.

These are the results for a cell with ZnCl2 15m + KI 5m in distilled water, MGL280 cathode, Zn anode, W42 separator. Charged to 1.3V, discharged to 0.5V at 5mA. Curves are cleaner than for a carbon cloth, EE is higher and CE is similar. There is an evident decay in capacity after 27 cycles.

I noticed that the original paper barely studies the effect of KI concentration, as they say that 5m is the highest concentration they are able to reach. However, I am able to easily dissolve 7.5m KI in the ZnCl2 solution, so I'm going to try that and see the effect it has on the battery properties. After that I'll study the effect of lower KI.

I have now assembled a new cell with ZnCl2 15m + KI 7.5m in distilled water, MGL280 cathode, Zn anode, W42 separator. I will charge to 1.3V, discharged to 0.5V at 5mA.

interesting to see variation between different trials with different concentrations, current density, charge voltage. thanks for the update!

Agree 100%, your experiments are great!

@curiouscarbon @svetz Thanks for your support guys, really appreciate it! ?