Would redox flow batteries be good for the development of all-electric armored vehicles?

Question

I am in the process of creating a somewhat hard military sci fi setting and was enamored by the idea of all-electric armored vehicles for a future war.

For this I decided to used Redox Flow Batteries: https://en.m.wikipedia.org/wiki/Flow_battery

I decided redox flow batteries were a good fit as it allowed the electrolyte of the batteries to be tranfered from one vehicle to another, meaning that armored vehicles could recharge themselves by filling up from a tanker vehicle that stored the electrolyte and recharged it using renewables or even portable nuclear sources.

This allows your "fuel" to be recycled between the tankers and the vehicles indefinitiely meaning that unless a tanker was destroyed or an accident happens and cause fuel leakage your forces could wove through wide swaths of enemy territory with minimal resupply.

They also have additional advantages of full discharge capability, very long cycle life, and have non-flammable electrolytes that don't explode like Li-ions.

Redox flow batteries are normally plagued with low power density issues however articles like the one below give me hope that future higher density electrolytes can be discovered:

https://www.sciencedaily.com/releases/2009/10/091012135506.htm

The above article claims they can now reach the equivalent density of Li-ions, so considering future technology, for the purposes of this answer assume maybe 0.5 times better energy density than current Li-ions.

Would this system work for the sustainment of an armored division on extended combat operations?

Answer 1

It sounds good for a story.

Let us remember that this is for a fiction and so should be cool for the readers or engaging for the players. It reads to me like you have your head wrapped around this concept well enough to bring it to life in your story. The idea of pumping electrolytes, tanker "refuel" trucks, soldiers with siphon hoses, fuel dumps etc has plenty of precedent in real militaries since WW1, and you can update and freshen this by making it electrolyte and batteries.

I have to say that in the real world I would rather have a lumpy box as my battery because I am certain electrolyte would somehow manage to spill in my lap because it always does and then they wont let me in the club. A soldier can grab the battery from a damaged vehicle and run with it; difficult with electrolyte or diesel.

Answer 2

Military uses will want compact fuel sources. The less weight of fuel they carry, the more weight of armor or shells they can bring. They aren't going to care much about the environment, except in terms of whose it is.

Bringing along a separate tanker means having a vehicle that can be targeted for attack to immobilize the others. The act of transfer might expose personnel or reduce the ability of the vehicles to maneuver. Also, is the tanker armored? If not, it limits the situations the whole group can enter. But if it is, why can't the other armored vehicles power themselves?

Mostly, I don't understand why the "renewable source" or nuclear source that you describe isn't right on the vehicle that needs the energy, instead of a tanker.

Update for specifics: if the battery has '0.5 times better energy density than lithium' (lithium + 50%), then I see 220 Wh/kg or 265 Wh/kg for that figure. "Wh" is an awful unit, J/s * 3600 s, so let's call that 954,000 J/kg = 954 J/g ... I'll be charitable and round it up to 1 kJ/g, then add 50% to 1.5 kJ/g. By comparison, octane has a fuel value of 41 kJ/g, and I see some figures for gasoline a bit higher. The site that says 265 Wh/kg above says gasoline is 100 times more energy dense than (less efficient, more widely used) lithium batteries.

It seems like common sense: If you load up a gasoline car with all the extra gas jugs it can carry, in the trunk and back seat and passenger seat until the weight capacity is maxed out, you expect it to go a long way; but if you double the batteries aboard an electric car, you would wonder if it could move. Electric cars have many advantages, especially since at lower fuel capacity the lack of engine weight makes a difference, but carrying troops a long way across hostile terrain in a barren war zone when resupply can't be guaranteed? I doubt it.