Why I'm Not Reinventing the Membrane

Nafion and FumaSep, both membranes are pretty expensive for me, and if they are expensive for me I don't think they would be any cheaper for any Flow Battery manufacturer. Because its basic economics, if your raw materials are expensive your end product can't be cheap.

So most flow battery manufacturers don't really bother with inventing new membranes, they use a material called DARAMIC separator, it is made up of Polypropylene (PP) or Polyethylene (PE) sheets with micro level holes in them, nothing new, its a 50 year old separator material which is used to separate positive and negative side. Daramic is used in literally all batteries, you name it, Lithium Ion, Sodium Ion, Lead Acid , All- Iron Hybrid Batteries and yes even Vanadium Redox Flow Batteries. 


There has been substantial amount of research on cheap membranes, but most of them last only a few weeks and the membranes that actually last.... well they are Nafion and Fumasep.

But Daramic works in a fundamentally different way than membranes, because unlike membranes, Daramic does not stop the negative and positive sides from touching, it actually allows the positive and negative sides to mix slightly, and this mixing facilitates exchange of ions. 

Now this slight mixing is not really a good thing, because in a flow battery it causes these problems -

1. Lower efficiency - Since the fluids mix, some charged ions are neutralized, this wastes energy, so in many cases if a Nafion membrane give 80% efficiency, a daramic separator can only give 70-75%

2. Fluid Crossover- Sometimes it happens that the pumps in the battery are not working in sync, one is pumping more fluid than the other, or putting in higher pressure than normal, in such situations the one side of the fluid literally goes into the opposite tank, (in my 2 cell mini battery run, my positive side literally emptied itself into the negative tank, GOD its a headache !!!!).

3. Self Discharge- If the battery isn't charging and sitting idle the fluids that are mixing will constantly touch each other and eventually neutralize the whole battery. This could be catastrophic. 

But these issues can be resolved by a well engineered battery.

  • It is acceptable to have a slightly lower efficiency battery because the cost of membranes is drastically lower. Daramic costs like Rs.150 ($ 1.50) per meter square, Nafion costs Rs 20,000 ($200) for meter square. That's more than 130x difference.
  • Fluid crossover can be balanced by carefully managing the pumps flow rate and pressure differences.
  • Self - discharge has an elegant solution - valves are used between pipes and tank to control the flow of electrolyte, so once your battery is charged, simply close the valves, like closing the tap when glass is filled with water, elegant right !!! 😁😁
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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