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NiFe Gassing

Hello, I've been experimenting with some NiFe cells from China on a solar powered shed and I have a questions about the electrolyte degradation.

Is it possible to stop the carbon build up by using pressurised recombiner vent caps like this one?
https://baterbattery.com/product/ba...combination-plug-recplug2-for-opzs-batteries/

Above is a link to this subject. Unfortunately "Mike 90250" passed away not long ago. He was one of the most knowledgeable and trusted persons when it came to NIFE information. The issue is not carbon buildup. Potassium carbonate is formed when carbon dioxide from the atmosphere is absorbed by the electrolyte. Some claim it is absorbed thru the plastic case of the cell as well as the fill cap area. Another argument is because they out-gas so much, the cells being at a positive pressure prevent or minimize the CO2 entrance thru the cap. In the end, CO2 does get into the electrolyte over time requiring periodic replacement.
 
Hello, thanks for the reply!

Damn... I noticed that there was this white powder forming around the top of the cells and couldn't work out where it was coming from. The stuff seems to get everywhere and has corroded the bottom of my metal box I've stored them in. I'm guessing the o-rings must be leaking somehow. The terminals are also corroding...

Is there anything I can do to improve the situation?
 
The white stuff is mostly potassium carbonate. It looks bad but rinses away with water. Wear chemical gloves when handling, and most importantly don't get it in your eyes - really bad !! It has a rather high (alkaline) PH. Close up photos of the terminals and filler cap area would help. How old, what brand are these cells?
 
They are from Seawill in china. They are a few years old and don't really do much other than power a ventilation fan to the box they are in and charge off solar panels. This is just a hobby I've picked up for testing renewable stuff.
https://www.alibaba.com/product-detail/Rechargeable-Nickel-iron-battery-for-sale_60173839439.html

The terminals are locally corroded black where I've affixed ring crimps for connection, I'm guessing it's the close proximity to copper is doing that.

I did some digging on the internet again and apparently rubber gaskets are air permeable, especially to carbon dioxide. PTFE seams to be an ideal replacement: https://www.marcorubber.com/o-ring-permeation.htm
https://static.thermoscientific.com/images/D20826~.pdf

I can swap out the O-rings around the terminals and my polypropylene cap adapter but inside recombiner plugs has a pressure relief valve which is inaccessible from the outside. No idea what material this is depending on where the recombiner comes from. (I've found 4 different manufacturers from the internet)

https://www.flowsystemsusa.com/battery-recombination-caps.html
https://baterbattery.com/product/ba...combination-plug-recplug2-for-opzs-batteries/
https://hydrocapcorp.com/
https://www.hoppecke.com/en/product/grid-aquagen-pro/
https://www.exponentialpower.com/pr...c/bi-directional-recombination-vent-caps.html
 

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Is the terminal stud smooth or threaded where the seal contacts it?
 
There are 2 orings per terminal. One is inside the cell against a smooth surface with a shoulder, the other is threaded and accessable from the top. There is a spacer plate inside between the 2. They both get squashed by a single nut from the top.

The design of these cells are not brilliant as they came from China but at this point, they are the only supplier that I'm aware of... (The Polypropylene case and rubber orings leak carbon dioxide into the cell, the vent cap that comes with them sometimes flood, the stainless steel terminal welds are corroded black inside and not bolted together with nickel plated metal. The plastic weld that binds the cell together seems OK though.)
 

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There are 2 orings per terminal. One is inside the cell against a smooth surface with a shoulder, the other is threaded and accessable from the top. There is a spacer plate inside between the 2. They both get squashed by a single nut from the top.

The design of these cells are not brilliant as they came from China but at this point, they are the only supplier that I'm aware of... (The Polypropylene case and rubber orings leak carbon dioxide into the cell, the vent cap that comes with them sometimes flood, the stainless steel terminal welds are corroded black inside and not bolted together with nickel plated metal. The plastic weld that binds the cell together seems OK though.)
Nice cells and photos! I think the slight pressure in the cell is forcing gas between the center hole of the washer and the threads of the terminal.
If these cells were mine, I would first try to replace the washer(s) under the stainless flat washer with a neoprene flat washer that had a center hole that is smaller than the stud. Thread it on like a nut. The undersized hole will force the material into the grooves of the treads forming a better seal.
If that does not work, I have sealed Edison nickel iron terminals with slow set grey JB Weld if it is available where you are. The method depends on how your cell is constructed. Are your cell plates touching the bottom of the cell case or are they suspended off the bottom held up by the terminal studs and nuts? Attached is a chemical chart for Potassium Hydroxide 50% solution. Yours is around 21% but I think the chart still applies. For the fill cap, the only thing that keeps them working is a periodic rinse with distilled water. I have also used a tapered neoprene stopper with a 4mm hole in the center. Insert a 4mm Teflon tube and vent to outdoors. If you use a rubber stopper, try to determine if it is low sulfur rubber. Edison had trouble with poor performance with the early versions of his cells and traced it back to the sulfur content of the internal cell spacers and insulators.
 

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To summarise my experience with the technology so far here it is:
  • The cell walls need to be made of ABS as polypropylene is gas permeable to carbon dioxide.
  • The electrodes need to be assembled with nickel plated metals to stop corrosion.
  • The rubber gaskets deteriorate and leak gas so need to be made of PTFE ideally.
  • Use catalytic gas recombiners to convert the explosive hydrogen/oxygen gas back into water.
  • Reduce charging voltage to reduce gassing at price of capacity.
  • Do not equalise when using recombiners as the high gassing will overwhelm them.
  • Do not over discharge as this will reverse the polarity of a lower capacity cell permanently damaging them.
  • Add only distilled water as anything else contaminate the electrolyte.
  • The electrolyte is made up of about 30% KOH and 1.5% LiOH, no idea if there are alternative chemistry to try.
  • The electrolyte mixture deteriorates over time when exposed to carbon dioxide.
  • The electrolyte chemistry is difficult to ship wet as are classified as hazardous.
  • There are no cell balancers or monitors that I'm aware of which go down to 1.4V
  • The cell separators need to be made of polypropylene to prevent sulphur contaminating the electrolyte.
Hopefully, someone can make use of my experience with the technology and make the situation better for others that are thinking about getting involved with the Edison cells.
 
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You can also paint the outer plastic with an oil based paint that is impervious to CO2. This can allow you to prevent CO2 flowing into the cell through the housing without having to change the entire body.
 
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