Quite interesting, I wonder about the capacity in amp-hours at any particular discharge rate.Usually a jump start takes less than a minute of cranking, even with a quite weak battery. So if it takes 100 amps for one minute that is 100 Amp-Minutes, =100/60 amp hour=1.66 Amp Hours.
But the big deal would be the cost, because the production of a nickle plate, graphite/carbon battery would be rather labor intensive. .And still we have the question of capacity, and the issue of physical durability, given the size and spacing.

 

Supercapacitors don't really have the issue of expansion or contraction like batteries. as theres no physical or chemical reactions like oxidation reduction or exchange of ions across a membrane like in a lithium ion battery so as long as there's no issues during assembly or physical abusive stresses afterwards. there shouldn't be any spontaneous short circuits or anything. and they should be quite stable
You can get nickel really cheap from some suppliers especially in thin sheets or thin rolls. and activated charcoal and graphite from the grocery store or online for really cheap. and for the binder you can use safe and affordable white glue like wood glue or other similar PVA adhesives as long as they don't dissolve in water.
The capacity isn't very high but the power density is where supercapacitors really shine. they can output massive currents rapidly. and be charged very rapidly in a compact portable form factor.
Supercapacitors do not change in capacity with discharge or charge rate. being nearly 100% efficient and able to deliver all of their energy as fast as one demands.

 

Supercapacitors don't really have the issue of expansion or contraction like batteries. as theres no physical or chemical reactions like oxidation reduction or exchange of ions across a membrane like in a lithium ion battery so as long as there's no issues during assembly or physical abusive stresses afterwards. there shouldn't be any spontaneous short circuits or anything. and they should be quite stable
You can get nickel really cheap from some suppliers especially in thin sheets or thin rolls. and activated charcoal and graphite from the grocery store or online for really cheap. and for the binder you can use safe and affordable white glue like wood glue or other similar PVA adhesives as long as they don't dissolve in water.
The capacity isn't very high but the power density is where supercapacitors really shine. they can output massive currents rapidly. and be charged very rapidly in a compact portable form factor.
Supercapacitors do not change in capacity with discharge or charge rate. being nearly 100% efficient and able to deliver all of their energy as fast as one demands.

Does this somehow relate to the post about batteries in post #20?? Not sure how white glue relates to a battery with an electrolyte. And I am trying to imagine jump starting a car from a small sized capacitor. I have seen photos of the commercial "super-caps" used for cranking engines and they are the size of a large car starting battery.

 

Nope. You can get lithium ion based and supercapacitor based jump starter booster packs that can jump start a car and fit in your pocket or be put in the glove box of the car.
Supercapacitors can be similarly sized and output hundreds of amps easily.
There are even supercapacitor jump starter packs that can charge off the residual voltage in your car battery if its not got enough to crank. and supplement the car battery long enough to crank the engine over to get it started.
Just search on amazon. supercapacitor jump starter pack and you'll see dozens of models for them. each with different functions and capabilities. and they are small and portable. You can carry them with one hand with two fingers.
They work and ive personally used one and seen them in action and they will absolutely crank over a car engine for a few seconds to get the car started.
Some of the lithium ion ones can even crank over the engine better and faster than the stock lead acid car battery some vehicles come with from the factory.

The white glue was referencing a binder option for the active material of the battery or supercapacitor to bond it to the current collectors. as a safe simple affordable and readily available binder option.

 

Got any pictures? Would be cool to see. I'm kind of looking for advise on alternative electrolyte chemistry for the existing Nickel Iron battery technology. I've got a test setup at home and looking to make improvements.

Just use potassium carbonate and call it good. it works. Very similar to potassium hydroxide. just lower conductivity.
Will not be prone to the effects of carbon dioxide absorption as it's already the carbonate form. and won't suffer the same deterioration. You could experiment with adding conductivity increasing additives like sodium sulfate in small amounts.
Maximum ionic conductivity for potassium carbonate is at 34% by weight concentration. so 34g potassium carbonate for 66g of water This would prevent precipitation as well. reducing the chances of carbonate precipitate buildups. Also relatively stable.
You could try zinc instead of iron as the negative electrode to see how that goes. May give higher voltage and performance. but beware the solubility of zinc oxides in the electrolyte.
Experiment with small scale sample cells if you like to see how different options work.
Make sure everything is sealed well and cannot leak out.