Why are there no flow batteries with symmetric ferrocyanide electrolytes? | Hacker News Reader

Why are there no flow batteries with symmetric ferrocyanide electrolytes?

chemisting.com

55 pointsDamonHD38 comments

Thank you for this, as somebody with almost no background in chemistry, I can now appreciate just a bit more the complexity that goes into battery development. Where does one learn about this?

Do a degree in inorganic chemistry?

Glad I finally have a name (flow battery) for a concept that I've been wanting to be made for a long time (liquid batteries).

You might find the home made batteries of this guy interesting as well https://www.youtube.com/watch?v=eq7fR9ISuCw

It's not a new idea, they already exist.

A huge redox-flow battery is currently under construction in Switzerland https://www.swissinfo.ch/eng/climate-solutions/switzerland-b...

A vanadium one, which (as mentioned in the piece) is symmetric.

The 'Just Have a Think' channel did a video on the Swiss battery here - https://www.youtube.com/watch?v=CPAFeTvjVzY

The advantage of vanadium batteries, as I understand it, is that leakage does not corrupt the system. The vanadium gets converted to the right chemical species on either side.

"We will be able to inject or absorb up to 1.2 gigawatt-hours (GWh) of electricity in a few milliseconds"

1.2GWh in a few milliseconds? I'm pressing (X) to doubt.

An energy comparison: a semi tanker of gasoline hauls about 300 MWh of chemical energy potential.

That must be the total capacity and response time.

Nope. Total capacity is going to be 2.1GWh. The peak power will be 1.2GW, and milliseconds is the response time of the system. [1]

[1] https://flexbase.ch/en

I would assume it's a typo on GWh. It seems probable to me that the battery can supply/absorb 1.2GW on a millisecond response time, so it would be able to fully charge/discharge in a little less than 2hours, supplying/absorbing 1.2GW with 2.1GWh total capacity.

They in theory combine well with pump-station powerplants where the medium is also the medium?

Flow batteries specifically are liquid, or more accurately fluid, there can be gas flow batteries, where the chemical sub-products are pumped in and out of the cells.

They tend to be large utility scale things that look like a chemical plant, correction, are a chemical plant with electrical storage as the product.

Liquid electrolyte batteries have been a thing from when batteries have been invented. But not much work has been done to really scale it up.

The idea has been kicking around for a while because it's superficially appealing.

Benefits:

- you can store huge amounts of energy in relatively cheap tanks

- because the + and - storage are physically separate, self discharge can be very low

- those two make it appealing for long term storage

Downsides:

- reagents end up being some combination of expensive (vanadium), poisonous, corrosive, etc. resulting in safety overhead

- requires specialized plumbing. This is very expensive. Ultimately this is the issue with nuclear as well, every joint requires careful inspection

- does not scale down nicely to house sizes

- ultimately likely to get economically lapped by incremental improvements to lithium or sodium battery chemistry

- the charge/discharge cell requires a liquid/liquid membrane separator which can exchange charge; these tend to have lifetime issues.

I’ve been sending these guys $10 a month for a while now. Thir test cell is chemistry agnostic, and I think they have tried several ferrous solutions. The membrane issue is not that big of a deal it seems if you aren’t trying to miniaturize the device- separator material used in car batteries can be used to good effect and it’s easy to replace if needed.

https://fbrc.dev/

I love this kind of work. They had an ambitious timeline and the last entry was at the beginning of this year -- do you have a sense if they are still going strong?

I’m really not sure. Things like this often run out of steam, get picked up later, etc as the interest and the lives of the people change, new people come, old ones move on. We will see.

Cyanide batteries... hmm..

*ferrocyanide Less toxic than cyanide.

Potassium ferrocyanide: 1.6g/kg LD50 Potassium cyanide: 5mg/kg

So cyanide is approx 320 times more toxic.

Exactly. Table salt has an LD50 of 0.5-1g/kg, 1.5-3x more toxic. I weigh ~85kg, I'd have to eat about 46 cubic centimeters of potassium ferrocyanide (on the conservative side) to consume an LD50 worth.

If you're talking about the chemicals in batteries we have today, the LD50 is probably way lower for most of them. If we're talking about batteries for consumer electronics, you'd have to eat (density wise) multiple batteries worth of potassium ferrocyanide to hit LD50.

Ferrocyanide is not dangerous. Sodium ferrocyanide is used as an anti-caking agent in table salt. It's considered safe for this use in both the US and the EU, e.g.:

https://ec.europa.eu/food/food-feed-portal/screen/food-addit...

Yes, but as the article points out, the process likes to evolve free cynanide in operation.

Putting stuff in electric fields while thinking "well, it's stable" is a fool's errand.

(As the article says...)

To give the answer its the cyanide part... which I knew already when looking at the title, without having much clue about underlying chemistry.

Good luck selling batteries full of some variant of cyanide to general public, i can almost imagine it working till people hear that keyword.

There are plenty of battery customers besides the usual suspects

Somewhat true, but consumers are buying vast quantities of lithium batteries and carrying them in their pockets. Those things are eager to catch fire and emit hydrofluoric acid.

You can have safe battery chemistry or useful battery chemistry. (Not an expert, open to correction.)

The public is not going to buy a flow battery anyway.

Or perhaps they will, but only when public is taken in the context as in public utility or public city. But individuals are not going to buy a flow battery, it is a chemical plant.

If we're going to do chemical-plant scale utility batteries, why not just lead-acid? It's well understood, simple, and the ingredients are cheap. Yes lead is toxic but it's easily contained and recyclable.

I think the very fact that PbS and for that matter NiFe have been around for decades and aren't widely deployed for utility scale probably counts against it. I suspect the answer may be that weight matters enough just in the cost of delivery to the site. Where utility scale storage is being deployed it's lithium; may switch to sodium as that crosses over in cost.

Have to abbreviate it as FCN. Cyanide is ~320 times more toxic than ferrocyanide.

Yeah, just like no one would ever buy a lead-acid battery.

I don't think many people are concerned about their batteries being safe for ingestion.

But toddlers could swallow it! Just like they swallow lead-acid batteries.

After all, people painted the walls and enhanced their gas with cyanide in large quantities for years before even realizing it had to be carefully handled so they are basically the same risk in the typical mind.

The problem is free cyanide is extraordinarily dangerous in the air and you'd likely kill a lot of people before someone realized what was going on with the battery, not just that people eat batteries. Even lithium batteries honestly get pretty close to not being worth the risk for consumers, cyanide is still a bit of a step after that yet.

Well they sell that liquid explosive terrorists use to make molotov cocktail firebombs, at every fuel station without particular volume limits at all. It's also sufficiently toxic that care is taken at salespoint to limit customer exposure to the vapours.

(these things are "all relative, if the value, measured in "convenience to the customer", is high enough, ways will be found to permit sale)

Vapor recovery requirements vary by locality. Where I live, none of the gas pumps have it.

well, if money were to be spent, in that case better build electrical charging infrastructure than upgrading the gas pumps ...

That's pretty much what the article states:

> When using ferrocyanide, also consider that while this salt is relatively safe in its unaltered state, subjecting it to electrochemical abuse WILL generate free cyanide and it’s likely to pose a significant danger to you and others. For this reason, I would recommend to stay away from testing ferrocyanides in symmetric systems entirely, unless you are a trained professional and professionally well equipped to handle both the potential operational hazards and wastes generated from its decomposition products.

Reply on news.ycombinator.com