SAFETY FIRST: This project is not for the timid. Wear goggles and gloves, seriously. see my previous
instructable for further details https://www.instructables.com/id/Create-a-recharga...
My goal, over the last four years, was to create a "good enough" battery for the billions who live in "light poverty" - 1.2-1.7 billion people who have no reliable source of light once the sun sets. Billions. So I decided that I can't help create a better LED, or necessarily in distribution, but I *COULD* help people build their own batteries for storage.
The first requirement was that the battery be cheap and easy to manufacture. It had to be an improvement over the toxicity of lead-acid, but could be as big and bulky as I might care to make it.
You can see some of my other instructables as steps toward this development.
What I've created is a wonderful 2.65v Aluminum-Ion battery due to an accidental discovery while exploring geopolymer-based electrodes for another cell. The aluminum silicates protect the aluminum from breaking down in the electrolyte, and allow the battery to work beautifully. I'm not 100% sure of the "final chemistry" of the cell, so I can't build one at 2.65 at the start, but the current cell (starting at 1.3-1.43 volts) can be conditioned to become the 2.65v cell over about 15 cycles. My "master" cell is still conditioning, so I'm not sure what the life cycle is at this point... but this is the best cell I've built in four years of working on it, and I want to make sure it's out there and ready.
0. Abundance - The battery should take advantage of abundant natural
resources, sticking within the top 10 or top 12 elements. (O, Si, Al, Fe, Ca, Na, K, Mg, Ti, H and possibly P, Mn)
1. A simple-to-make battery that could be constructed in primitive conditions
2. It should be easily constructed from recyclable/recycled materials "Junk"
3. It should provide enough power to light LED lighting systems through the night
4. It should be rechargeable
5. It should be easily deconstructed, "serviced", or recycled once it fails.
6. Open Source- the "recipe" will be freely available for anyone to use.
0. Carbon, because it's hard to make a cell without it, and is generally accessible. Sulfur as well, again, because it's generally accessible by consumers (battery acid is a common thing).
1. Size - I don't care if it takes up the size of a chair, up to 5 times equivalent size lead acid
2. Voltage - I'm not worried about a low voltage cell, if I can just stack several together
3. Graphite - While not ideal for primitive situations, it can be easily recycled from dead primary batteries
4. Time to condition - it might take a while to condition the battery to a useful state through repeated charge/discharge cycles
5. "Outgassing" - while a serious negative, it is understood that some outgassing may occur during conditioning. Gasses like Chlorine might require the battery to be stored outside.
6. Boost converter - Our goal is to create light, not worry about continuous voltage - so a pulsed boost converter is acceptable (a "Joule Thief") to get a lower voltage up to a pulsed signal capable of lighting an LED. I've driven "30 watt" LEDs on as little as 2 watts using this method.
My original cell is actually the "Variant: Scrap Aluminum Tubing and Graphite stick" later in this instructable. This instructable is my first attempt at a flat cell. Below is the ingredient list, construction, and what I believe is the theory behind the cell.
The very basic ingredients:
Waterglass - Sodium Silicate - doesn't take a lot.
Basic build process: (the aluminum tube variant is recommended)
1. Paint the aluminum surface "inside" with waterglass (sodium silicate). It will react and form a white gel, and a dark gel. It will produce hydrogen and heat up during this reaction.. so be careful.
2. You can place a paper seperator on top of this, as well as wave paper, and let it sit for 24-48 hours
3. Mix a slurry of urea, salt, borax, and epsom in equal parts. You may also add a small amount of waterglass to loosen it.
4. Spread the mixture on the paper seperator
5. insert/overlay with your graphite electrode. You may also try copper, but I haven't tried that yet. You will likely have a slighly lower voltage ~ 2.25v
6. The cell should have an initial voltage around 1.3-1.4v - I'm not 100% sure why... but that gives you a clue it's working.
7. charge >3.5v, discharge through a white LED. higher voltages (4v - 10v) are possible, but will create chlorine gas, which is bad news. This doesn't seem to ultimately affect the battery as far as I can tell. It may bubble over with what appears to be water with dissolved AlCl. Not good for you to touch or ingest.
8. Occasionally let it sit overnight without a charge.
9. repeat 6/7 - and the battery will slowly improve.
10. The cell can be smelted down into aluminum when you wish to recycle it.. you may wish to add lye to deactivate any salts in the electrolyte.
11. The first 10 or so charges can be a little disappointing. Keep it up, you'll see it gradually improve.
My working theory:
1. Waterglass (Sodium Silicate) reacts with the Aluminum to form (Aluminum Silicate - a relative of clay). This is the "white gel"
2. The "free" sodium will react with water to form lye (NaOH).
3. The lye reacts with the aluminum to form Aluminum hydroxide (and hydrogen)
4. The borax (Sodium tetraborate) and Salt (NaCL) already have sodium ions, so don't react
5. The magnesium sulfate I added since magnesium is far more reactive than aluminum, and I believe might help maintain the electrolyte. It may not be necessary
6. Overcharging the cell will change NaCl to NaOH and Chlorine.
7. The Chlorine reacts with AlOH and Al to form AlCl
8. The urea then helps for a Deep Eutectic Solvent with the AlCl, acting as our electrolyte.
9. Aluminum ions get intercalated in the graphite, but will rejoin with the Aluminum silicate on discharge
10. I believe the Aluminum silicate and Sodium silicate are the "merry go round" that causes the process to work, and that we, as we get to less and less water in the mix, find a perfect balance that allows the battery to work well.
11. I'm not sure the borax and epsom are needed, but in my experience they make batteries work better.