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Is this the Holy Grail of home energy storage for DIYers?
#11
I just thought of something! The levelized cost of energy stored (LCOES) for the minimal architecture zinc–bromine battery is considerably less than the other batteries. But it's even better than that for DIYers. DIYers can reuse components, such as the case, terminals, and electrolyte too (so I read). If you design your cell right, you should be able to open it up (after discharging), and remove and replace the electrodes, and maybe make some adjustments to the electrolyte.

Edit: Cell size should be taken into consideration too. If the cell is small, the cost to replace a single cell's electrodes is cheap, but when you need to replace many or all of your cell's electrodes, you'll have a lot of work. If the cells are larger, replacing many or all your cell's electrodes will be less time consuming, but you'll spend more money when you need to replace a single cell's electrodes.
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#12
Sounds like it's not new science, so it must have its downsides. From looking at the video briefly, I can see determining full charge is based on a 'dip' so a cc/cv charging is not possible. If this was viable and affordable then it would have made it mainstream. Who knows it might, if there's a way to do it. It's akin to the edison battery, which I think would be easier to build and source diy. Nickel and iron would be the metals and potassium hydroxide which is a semi-common food or soap making powder.
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#13
I've compiled a list of design / operating suggestions from the comment section of Robert's video, and from what I've learned from reading the research papers, and other sources. I also explain how to create a carbon foam electrode (CFE), and point out the cost for materials in order to reach the projected levelized cost of storage (LCOS).


Cell Design Suggestions

a. Space top and bottom electrodes 0.4 cm apart. This was determined to be optimal spacing, according to Princeton's research.

b. Use 1.0 M ZnBr2 electrolyte. Despite Robert's comment of 1.75 M ZnBr2 electrolyte, 1.0 M was in fact determined to be optimal in terms of the lowest LCOS, according to Princeton's research.

c. Do NOT use a supporting salt to reduce resistivity, despite Robert using 1 M of sodium sulfate. Princeton tested supporting salts (including sodium sulfate), and found that the best supporting salt (sodium chloride) decreased performance significantly as it created high levels of hydrogen.

d. Use a carbon foam electrode (positive), opposed to the carbon felt electrode in Robert's cell. Doing so produces greater coulombic efficiencies, resulting in as much as 10% greater energy efficiency, according to Princeton's research. Note that a carbon foam electrode which is hollow on the inside (shell) will hypothetically increase cell capacity, according to Princeton. However, this makes the production of CFEs more complex, opposed to a solid foam piece.

e. Use a carbon cloth electrode (negative). Both zinc and titanium (having good resistance to the electrolyte) negative electrodes were tested, however, their outputs were unstable opposed to the carbon cloth. Princeton also stated that to improve cell performance that they began "double-bussing" the carbon cloth. I think that means doubling up on the carbon cloth..?

f. Both carbon electrodes should have aluminium (affordable) current collectors coated in carbon to protect them from the electrolyte. This is just my opinion.

g. Invert electrodes (positive on top, negative on bottom), opposed to Robert's design. Princeton's exemplary battery design inverted the electrodes. By doing this, the top carbon foam electrode reacts with the hydrogen as it bubbles to the top, and redissolves it back into the solution, "thus recapturing any potential losses."

h. For a 48V battery, 30 cells in series may be optimal. The Redflow ZBM2 Battery (a zinc-bromine flow battery) has a operating range of 40-57V, and has 30 cells in series. I imagine this is for good reason (for inverters/charge controllers?).

i. Shorter charge/discharge times (e.g., 4-hours, 8-hours, 12-hours) offer the lowest LCOS because shorter cycles allow more cycles during its lifetime, and there are lower self-discharge rates per cycle, according to Princeton's research.



How to make a carbon foam electrode (general information)

To make 1 kg of carbon foam material, combine 425 g of carbon black (powder?) with 425 g of graphite (powder?). Next, create a solution of polyvinylidene difluoride (PVDF) in N-Methyl-2-pyrrolidone (NMP). NPM can be found on ebay. It used to be a common paint stripper. Properly mix a solution of 150 g of PVDF with 2.85 kg of NPM with a magnetic hotplate with a lid on the glass beaker. Pour the solution in with the carbon mixture, and mix to create a carbon slurry. Pour the slurry into a mold(s) to create your desired shape and size CFE.

Princeton's CFE was cylindrical. They created a 3D printed retractable piston to compress the slurry down in the mold using a hydraulic press to ~1 psig. With a little ingenuity, you should be able to compact the slurry @ ~1 psig without a hydraulic press.

Finally, put the mold(s) in a vacuum oven, and baked for 8 hr at 130 °C, evaporating the NMP and leaving behind a porous but rigid carbon foam. Time and temperature may vary depending on the size and shape of your CFE. I estimate the weight of the large cylindrical CFE which Princeton created to be around ~24.5 g when calculating your oven temperature and time.

WarningN-Methyl-2-pyrrolidone (NMP) is not safe. Research it first. Never allow NPM to contact your skin or eyes, and avoid inhalation, using excellent ventilation.



**Cost of materials to reach the projected LCOS (according to Princeton)

  Plastic (HDPE or PTFE) cell case: $0.22 - $0.37 per liter (volume within case)

  Zinc bromide (anhydrous): $2.30 - $3.10 per kilogram

  Carbon foam electrode: $5.70 - $11.20 per kilogram

  *Carbon cloth and Titanium current collector: $13.10 - $19.10 per square meter

* Note that this cost is bundled, and the the titanium current collector was used on the positive electrode. A more affordable solution may be to use aluminium current collectors coated in carbon to protect it from the electrolyte. Although, maybe titanium alone is the more affordable solution, as it has good chemical resistance to the electrolyte, and therefor may not need to be coated in carbon (or plastic).

** Note that to reach these figures you're most likely looking for technical (industrial) grade materials, or battery grade. Avoid expensive laboratory and reagent grades.
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#14
(01-27-2020, 02:42 PM)vspin Wrote: **Cost of materials to reach the projected LCOS (according to Princeton)

  Plastic (HDPE or PTFE) cell case: $0.22 - $0.37 per liter (volume within case)

  Zinc bromide (anhydrous): $2.30 - $3.10 per kilogram

  Carbon foam electrode: $5.70 - $11.20 per kilogram

  *Carbon cloth and Titanium current collector: $13.10 - $19.10 per square meter

* Note that this cost is bundled. A more affordable solution may be to use aluminium current collectors coated in carbon to protect it from the electrolyte. Although, maybe titanium alone is the more affordable solution, as it has good chemical resistance to the electrolyte, and therefor may not need to be coated in carbon (or plastic).

** Note that to reach these figures you're most likely looking for technical (industrial) grade materials, or battery grade. Avoid expensive laboratory and reagent grades.

Do you know where those prices may be found for example the Zinc Bromide. Here in Canada I could almost buy a car for the price of a 1kg.
Also being Anhydrous how are many of the companies storing it in paper bags or cardboard containers etc?
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#15
(01-28-2020, 12:55 AM)Bubba Wrote: Do you know where those prices may be found for example the Zinc Bromide.  Here in Canada I could almost buy a car for the price of a 1kg.
Also being Anhydrous how are many of the companies storing it in paper bags or cardboard containers etc?

Honestly, I don't know why it would be stored in paper bags or cardboard unless lined with plastic. I would expect in the very least that it was stored in plastic (zinc bromide resistant) bags. I think you will have to purchase from China (Alibaba).

EDIT - Here is zinc bromide (99%+ purity) at $1.00 per kg which requires a minimum 10 kg order:

https://www.alibaba.com/product-detail/H...73748.html


I don't know how accurate, or current the listings is, and whether or not the supplier is reputable, however, this Gold supplier has a high Response Rate, and number Transactions. You can find other substances on there as well (e.g., battery grade carbon black and graphite).

You can also purchase samples (sometimes free, if you pay for shipping) from some suppliers. This may be a great option if you only need a small amount.
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#16
They cheapest i could find is the one used at oil rigs for drilling, but its not very pure ~70%
For school projects i could buy some but at a very high cost.
To make zinc bromide myself, to time consuming.
I sended a email to two chem suppliers(they only deliver to resellers or big quantities to companies) here in the Netherlands.
No shots fired = always a miss.
I suspect the rest of the ingredients is going to be way easier.
Overall it sound like a fun project.

@vspin,
I ordered two times via alibaba direct from factories/mines.
one time not even a shipment the other time 50% pure instead of 99%.
Both orders was for antimony and bismuth.
I don't say this one is bad, perhaps i am even going to try
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#17
How can you tell what the purity of the compound is? Any of the above listed.
Proceed with caution. Knowledge is Power! Literally! Cool 
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#18
(01-28-2020, 12:44 PM)100kwh-hunter Wrote: @vspin,
I ordered two times via alibaba direct from factories/mines.
one time not even a shipment the other time 50% pure instead of 99%.
Both orders was for antimony and bismuth.
I don't say this one is bad, perhaps i am even going to try

Indeed, doing business with China is painful, but necessary to keep costs low. Although a supplier can bait (with sample) and switch (with large purchase), I recommend that you get samples first before investing a lot of money, and that you look for:

1. Orders with Trade Assurance. Make certain that purity is disclosed in your order.

2. Suppliers with high response rates.

3. High number of transactions.

4. Rated high with several years in business.


(01-28-2020, 05:59 PM)Korishan Wrote: How can you tell what the purity of the compound is? Any of the above listed.

According to Sc
iencing, there are four methods:
  • A visual (and taste, if edible), physical comparison with a "certified" pure sample.
  • By comparing the melting and boiling points of the substance with the pure substance.
  • Colorimetric method which introduces a chemical(s) to turn the impurities a certain color. This method is "designed to determine the presence of impurities, not to determine the amount or the percent purity of the substance."
  • The analytical method (most accurate method) "mostly involves chemical analysis, which can pinpoint the presence, identity and amount of impurities in the sample."

Edit: I suppose you were actually looking for specifics for the listed items, opposed to general methods.


Edit: [incorrect content removed]
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#19
https://scholar.google.com/scholar?hl=nl...ttery&btnG=
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#20
Good morning.
For so far my reading and understanding of his video's goes:
They are very simple to make.
Chemicals are (theoretically) easy and cheap to purchase.
A cell with dimensions of 10x10x2.5cm or 4x4x1 inch, will give you ~1.85v and ~2000mah storage max.
Side note: its 100cm2 / 15,5inch2, will give ~2000mah
Length and width of your cell can depend and vari on the width of your purchased material.

The max storage capacity is also depending on the chemicals you are using (and filler, solidifying agents)
It is possible to make a "dry" maintenance free (gel like) cell.
But the cathode and the anode must be at the top and bottom. Not at the sides, not even if you would use filler and a solid gel electrolyte(zinc bromine based).
There are claims that those cells could have 10.000!! cycles.

If you would stack them on top of each other(connected with graphite sheets in between) you can stack them up to max 7 pieces ~12v.
Put a supporting case around it and continue stacking.
For a 48v @ 2ah cell it would be 4x4 by 20-25 inch high/10x10cm by 50-60 cm high.
For a 48v @ 200Ah = 1550 inch2 / 1m2
For comparison lifepo 48v@200Ah you would need: 550 inch2 / 0.36m2
Lifepo is roughly one third at surface area and half the height.
And 3 times more life.

So far, so good.
What I think what is the real problem is that charge/discharge vs storage ratio. 1 to 10
To charge or discharge with 10a you would need 100a of storage

Lets see if i can get all the materials needed and give it a go.
Word of advice: check your country's laws regarding those chemicals and diy ess.

Any thoughts? Thanks in advance.
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