How difficult would it be to make zinc-bromide flow battery. One – or a few smaller units to total – about 20 kW/h ?

Spiny Norman said:

How difficult would it be to make zinc-bromide flow battery. One – or a few smaller units to total – about 20 kW/h ?

Whew, that’s technical. I’m only familiar with the vanadium redox and organic flow batteries.

As you’re aware, the big advantage of the flow battery is that it can be discharged and recharged an exceedingly large number of times without degradation. This has, if I remember correctly, led to it being installed in conjunction with the King Island wind power station.

These days, lithium ion technology has improved enough to make it outperform the flow batteries, particularly in terms of weight because lithium is the lightest weight metal. Also, because of economies of scale, lithium is now mined in such quantities as to reduce unit cost. Together, they explain why lithium ion is the battery of choice for electric cars.

CSIRO has been working on improving lead-acid batteries which to me at first sight seemed ridiculous, but now that I’ve learnt more makes sense because of the way they’ve turned them into a combination of battery and supercapacitor in a single unit, allowing a very rapid discharge rate without degradation.

Now back to the topic. Zinc-bromide flow battery – about 20 kWh ? Have to look it up.

Flow battery: “The redox (reduction–oxidation) cell is a reversible cell in which electrochemical components are dissolved in the electrolyte. Older zinc-bromide cells reach 70 Wh/l. For comparison, lithium iron phosphate batteries store 233 Wh/l. The zinc-polyiodide battery is claimed to be safer than other flow batteries given its absence of acidic electrolytes, nonflammability and operating range of −4 to 122 °F (−20 to 50 °C) that does not require extensive cooling circuitry, which would add weight and occupy space. One unresolved issue is zinc build-up on the negative electrode that permeated the membrane, reducing efficiency. Because of the Zn dendrite formation, the Zn-halide batteries cannot operate at high current density (>20 mA/cm2) and thus have limited power density. Adding alcohol to the electrolyte of the ZnI battery can slightly control the problem.”

Hybrid flow battery: “The hybrid flow battery uses one or more electroactive components deposited as a solid layer. In this case, the electrochemical cell contains one battery electrode and one fuel cell electrode. This type is limited in energy by the surface area of the electrode. Hybrid flow batteries include the zinc-bromine, zinc–cerium, lead–acid, and iron-salt flow batteries.”

The big advantage of the zinc-bromine hybrid cells seems to be the large number of charge-discharge cycles. More than 2,000 cycles. Zinc-bromine hybrid flow batteries have an energy storage of only 75 Wh/Kg, of similar magnitude to the 70 Wh/l of the zinc-bromide flow battery.

Zn polyiodide may increase that 70 Wh/l to 167 Wh/l.

For 20 kWh with a zinc-bromide and technology from 2015, it would require 20,000/70 is nearly 300 litres, which is a box 1 metre by 1 metre by 1 foot. Out of the question for an electric car, but physically possible for an electric train or ship.

Battery technology is increasing so rapidly that a good research effort could change all the numbers around in a decade, or less.

Let’s have a look here, it’s a proposal from 2013 for using zinc bromide flow batteries for wind farm use.
https://sci-hub.tw/https://ieeexplore.ieee.org/abstract/document/6488822
That’s a 50 kWh zinc bromide battery system.
“The dimensions of a 50-kWh zinc bromide battery are 4′(width) by 4′3′′(length) by 7′4′′(height).”

I’ve never made one.

I can tell you that 20 kWh will require about 250 L of fluid.

There are DIY videos. I suspect that it’s fairly easy to make a working flow battery that has nominal kW/kg (after all, it’s not fundamentally rocket science) and harder to make one that has a great W/kg.

https://www.youtube.com/watch?v=qOOu-XhbfPg

Ta blokes. Just having a look at the options for a home battery, so size & weight aren’t a problem at all.

I’ve never worked with them and having a look at the wiki article on them I’m not sure I’d want to. The care and maintenance on these things seems very onerous for a home style installation. It just seems that if you left them to their own devices for a week or two you’d screw them.