My adventures building a Zn-MnO2 battery

[danielfp248]

After 107 cycles there are no signs of degradation (the small drop at cycle 65 was because my computer restarted and I had to restart the testing process). Both charge and discharge potentials have started to stabilize. The battery has a CE > 95% and EE > 80%.

 

[danielfp248]

After 123 cycles, everything still stable. Charge/discharge potentials continue to stabilize.

 

[svetz]

Wow!

That's already looking better than an average Lead Acid battery which has a CE ~85%, EE ~70%, and at 100% DoD capacity starts dropping after ~100 cycles. Wonder how the $/kWh and Wh/kg compare to LFP (as I recall, you said in the OP they were "low cost")?

 

[danielfp248]

Wow!

That's already looking better than an average Lead Acid battery which has a CE ~85%, EE ~70%, and at 100% DoD capacity starts dropping after ~100 cycles. Wonder how the $/kWh and Wh/kg compare to LFP (as I recall, you said in the OP they were "low cost")?

Lead acid is at 80-90 Wh/L. This is at currently less than 1/4th of that. We will need to see if we can reach those types of capacities!

The cost relative to lead acid should be substantially less if we do get there.

 

[danielfp248]

I stopped the test at 137 cycles. I will now be doubling the capacity and trying to charge to 2mAh at 5mA and discharge to 0.8V at the same current. This would bring the energy density to ~30Wh/L.

 

[danielfp248]

This battery failed quite quickly in the 2mAh test. The test was also quite slow, so I increased the current to 10mA, which was likely too much, as potentials increased all the way to 2.4-2.6V on charging. Upon opening the battery I measured the thickness of the device, which ended up being 0.4mm. The zinc anode showed clear signs of corrosion.

To continue, I have started Exp34. This test used a carbon cloth cathode, 3 layers of fiberglass filter separator, zinc anode and a solution containing 1m ZnSO4 + 1m MnSO4 + 8m urea in a 10% acetic acid buffer at pH 5 (adjusted with potassium carbonate). The idea of the urea is to decrease the water activity to see if this helps with both dendrite formation and hydrogen evolution.

I have started cycling this battery to 1mAh, at 5mA, discharging to 0.8V. This puts the energy density at around 23Wh/L. The battery is behaving in a stable manner after 111 cycles. The urea did diminish the conductivity of the solution, which increased its series resistance and diminished both energy efficiency and the average discharge potential. I will cycle it 500 times (if it allows me to do so) and will then open it up to see if there is in fact corrosion of the zinc anode.



For the next experiment I will likely try decreasing the pH5 buffer content to get a more concentrated urea + Zn + Mn solution. But I will decide once this text is done. If the urea does nothing to prevent corrosion then I will try a test with higher ZnSO4 concentration.