Iron Battery - What Worked and What Didn't

When I left the Iron Redox Flow Battery overnight connected to the AA battery, and switched on the pumps again in the morning, I immediately noticed brown liquid flowing through the pipe into the tank, so I asked AI what happened (novice here too !!😇), then I had to understand how exactly a battery works.

So buck up, now we are going into depths of battery science, but first the basic-
Current is how many electrons can you push in the circuit per second, voltage is how hard you can push them, current density is how many electrons can pass through battery electrode per unit area per second.

The higher the current density; faster the battery charges, lower the current density; slower the battery charges. But remember, per unit area, so the total amount of current flowing in the battery is dependent on area of the electrode also. A good battery crams as many electrons possible as quickly as possible in a unit area of the electrode. For instance, when you connect a fast/turbo charger to your smartphone, it pushes around 7 mA/cm2. When you use the phone, you are discharging mostly below 1mA/cm2, that's why you can use the phone for 7 hours without thinking twice.

But this is not your phone's battery, this is a battery for kW level storage, its current density starts with 40 ma/cm2. A vanadium battery operates above 100mA/cm2. Iron battery, charges around 40mA/cm2. The AA cell charges our Iron battery at around 12 mA/cm2. Excellent for a phone battery, horrible for a grid battery. So the battery took the whole night to charge, not fully, just the liquid in the cell. To see a significant amount of color change, it took around 2 days. But it charged, and eventually my multimeter gave 1 V reading.



Battery after overnight charge with pumps off

On the third day, that 1 volt reading started going down. That means the battery started eating itself, this is called self discharge, why did this happen ? Well, because I used a cheap Daramic separator to separate positive and negative side of the battery. Eventually, the liquid on both sides started mixing and neutralizing each other, this is called crossover. 

Ideally, I should have used an Ion Exchange Membrane ( like Nafion or Fumasep) but I was broke and membranes are expensive (Rs 4000 or $ 40). And physics doesn't give free lunch.

So I was satisfied with the battery, first test, not so bad right ? So I opened the stack, and found a hole in my Daramic, and a rust particle puncturing it. What was this ? Well it was the dangerous assumption we made in the last post that Iron battery and Vanadium batteries operate the same way. 

They don't. More on that in the next post.

None of this is AI generated, so feel free to fact check me and looking forward to your views and help. 

Mayank Jately

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