Introduction: Aluminum Can, Saltwater and Charcoal Battery

Picture of Aluminum Can, Saltwater and Charcoal Battery

This instructable shows how to create a simple aluminum air battery from a soda can and a piece of charcoal from the backyard BBQ. This instructable is being published early but I hope to combine this device with a joule thief and an LED to provide a rechargeable backyard lighting system that can be emptied and refilled.

I believe that well burned campfire charcoal could also be used. Backpackers could have an extremely lightweight, wholly renewable and non CO2 generating light source.

From Wikipedia:Aluminum Air Battery
Aluminium batteries or aluminum batteries are commonly known as aluminium-air batteries or Al-air batteries, since they produce electricity from the reaction of oxygen in the air with aluminium. They have one of the highest energy densities of all batteries, but they are not widely used because of previous problems with cost, shelf-life, start-up time and byproduct removal, which have restricted their use to mainly military applications. An electric vehicle with aluminium batteries could have potentially ten to fifteen times the range of lead-acid batteries with a far smaller total weightt.

Step 1: Bill of Materials

Picture of Bill of Materials
We'll need:

An aluminum can. I use a soda can.
A piece of sandpaper. I happen to have some sticky sandpaper for a sanding block. Very convenient. This is used to remove the surface treatments from the can. This actually may be optional. I will experiment and update the instructable appropriately.
A sponge. This will be cut to fit inside the battery. I used a cellulose sponge from a 6 pack my wife had under the sink. A natural sponge may be more conductive.
A charcoal briquet.
Several readers have suggested alternative, readily available carbon sources. The most scientific sites I've visited have recommended activated charcoal for the carbon electrode.
  • Britta disposable filters
    • Aquarium filter charcoal
1 gallon plastic garbage bag
Rolling pin or short piece of pipe for crushing charcoal
Duck Tape - That's right its called Duck Tape, not Duct Tape.

Some copper wire or copper mesh. The effectiveness of this device is directly linked to connectivity between the copper drain and the carbon cathode. Also it is not possible to solder a lead to the aluminum.

I am using copper mesh and foil from K&S Metals to obtain connectivity. In the first release I tried a simple copper mesh/carbon combination that generates power but I am working on second generation and will update the instructable when it's available.


Step 2: Preparing the Anode

Picture of Preparing the Anode

Okay, first we're going to remove the surface treatment from the inside and outside of the can. It's not clear to me that the outside really needs to be stripped but hey it looks cooler that way. There's another instructable in which the author demonstrates a really cool way of cutting the bottom off of a soda can smoothly. The arrangement is shown but didn't work very well for me so I resorted to using household scissors.

Cut the soda can by whatever means about 1.5 inches high or about 1 inch above the lower rim. Using your sandpaper sand the inside lightly to remove any anti-oxidant coating.

Prepare enough warm salt water solution to fill the container. Use warm water and enough salt that it won't dissolve. Stir the solution to faciltate dissolving the salt and set aside.

In the Mark II I will be attaching a copper lead to get a good electrical connection with the can. Since aluminum cannot be soldered we're going to secure our drain mechanically with tape. We're going to use Duck Tape which was invented during WW II by Johnson and Johnson when the U.S. Navy needed a durable waterproof tape for use in the field. I understand this position is akin to posing a solution to "who writ Shakespare" but there you have it.

Step 3: Preparing the Cathode

Picture of Preparing the Cathode

The cathode is a carbon cathode with a copper lead to complete the circuit. The sponge is used to provide a bed to rest the carbon on. The copper mesh is secured to the grid and the carbon is heaped on top of it.

Take the sponge (dry is easier), invert the anode over it and draw a circle.the diameter of the can. Cut a circle from the sponge slightly smaller than the circle. The sponge will expand so you want to leave 1/8" or so all around.

Take the charcoal briquet and break it up into smaller and smaller pieces until you have a reasonably fine powder.

Put the briquet in a 1 gallon plastic garbage and break it with a hammer. Take care not to puncture the bag. I used a short length of PVC pipe as a rolling pin to grind down the charcoal. Remove any unburned particles of wood that you see.

The finer you make the powder the more power transfer will be available. Or at least that's my understanding. Its not clear at this point how much carbon is required in the cathode.

Step 4: Assembling the Battery..

Picture of Assembling the Battery..

Okay Macgyver we're off and running.

Place the sponge inside the aluminum can and pour in the salt water gradually allowing the sponge to expand. When the water just comes to the top of the sponge place the copper mesh on top of the sponge making sure it lays flat.

Now carefully pour the crushed carbon onto the copper grid.

Attach one lead from the voltmeter to the can, attach the other to the copper mesh. In this particular shot you can see the multimeter showing 3.6 mA, the intro shot shows the .5V reading.

If I've been reading everything correctly I believe this can be hooked up to a "Joule Thief" to power an LED.

Look for continuing updates to this project to reflect the Mark II design.


Aritusa (author)2009-05-26

Actually aluminum can be soldered, check out this site for an easy solution www. solder-it. com they have an aluminum soldering paste that also works with soldering aluminum to dissimilar metals. There are also special brazing rods for aluminum.

egbertfitzwilly (author)Aritusa2009-05-26

How to solder some of the more difficult metals such as aluminum would make an excellent and extremely useful instructable. I don't think most of us have ready access to welding equipment unless I can make an easy arc welder from like a boatload of aluminum cans....

Aluminum has a extremely low melting point. You can melt it over a small fire. If you had a really hot soldering iron, you could probably work with that.

AdrianG139 (author)Speedmite2017-11-28

Not that low. It is 660 degrees C. Lead is 327, Tin is 232 although Gold is 1,064 and Iron is 1538. Your soldering iron would need to be a very hot one.

static (author)egbertfitzwilly2009-06-02

The AlL "brazing" rods available only need a common simple propane torch to use, for small projects that don't sink the heat away fast. Their down side can be cost. Unless you find a motivated carnival/fair demenstrator with a large stock of the stuff to move. For most tape or alligator tips would work well enough.

germeten (author)egbertfitzwilly2009-05-29

Alumalloy welding rods, let you weld AL with just a propane torch. Bend-&-crimp works too.

maxhuey made it! (author)2017-03-01

Maybe find a way to get more air into the battery through the carbon electrode...

If you look at the picture of Fuji Pigment battery, they were able to get more air through the carbon electrode without leaking electrolyte out.

kedaar behera (author)2016-05-05

very good doud .

macrumpton (author)2009-05-28

Very cool projectIf you used the full height of the can wouldn't you get more output? For that matter what about using a 5 gal paint bucket lined with aluminum foil, or aluminum flashing? Back when I was a kid the microphones from telephone handsets used carbon somehow. I am not sure whether it changed the resistance proportionally to the sound or whether it actually generated power.

static (author)macrumpton2009-06-02

This is a primary battery. A larger physical size will only mean more total current will be available for use. As I recall the voltage that a battery can deliver has something to do with the location of the electrode materials on the periodic table of the elements. This supports my recollection, but doesn't give the "why" or The answer of why may be hidden somewhere in this search or I'm running behind with reading this weeks weekend builder so I'll let you have at it., if you wish :)

franken_stein (author)static2009-07-31

Actually, you should check out the reactivity series. For a battery, the further apart the materials are in the reactivity series, the more current generated. If I am not wrong...

static (author)franken_stein2009-08-12

Yes is the reactivity series it seems, but from what I can tell it still determines the battery voltage. I'm not to say anything for certain the topic gets pretty deep,too deep considering the point I was trying to make. That a factor other than pysical size determines output. Output was undefined in the comment I responded to. I assumed voltage because power (E x I=P) is rarely used to refer to the output of a battery.

egbertfitzwilly (author)static2009-08-12

Because the electrolyte and anodes can be replenished I believe this is properly called a fuel cell. If it were sealed it would be a battery.

It is my understanding, from sources I can't quote offhand, that Al-Air fuel cells (replenishable) are the leading candidate to replace conventional rechargeables in netbooks and cellphones. The most common battery type used in hearing aids is Zinc-Air so this makes sense.

Wikipedia has the math but it doesn't explain it:

"About 1.2 volts potential difference is created by these reactions"

I'm too stupid to figure out +2.71, +.40 and -2.31 produce a potential difference of 1.2.

Not a fuel cell, an electrochemical cell. A battery is just a group of cells. For example, a 9-volt battery is just six 1.5 volt cells connected in series. Cut one open and check it out. Technically, a AA battery is a cell, not a battery. A car battery, a lantern battery, and a 9-volt battery are all true batteries.

egbertfitzwilly (author)static2009-08-12

I believe its the electrode potentials rather than the basic reactivity series alone that determine voltages from a cell. This appears to be a standard table:

Now if I can just figure out what the entries mean I'll be set....

Moto13 (author)static2009-06-08

>This is a primary battery. A larger physical size will only mean more total current...something to do with the location...on the periodic table... Yup! As the electrons jump up/down from differing atom's electron shell sizes they release a proportional voltage and amperage...thas why to increase it you have to stack in series( + to - , for double voltage), or in parallel( -/- & +/+, for double the amperes).. most batteries are many "cells" in series, like a car battery that has 6 pairs of plates wired together to make 12 volts.. hope this clears it up least a bit :) Moto13

Yes, the device can be scaled up quite nicely. The only gotcha is that scaling up increases the current but not the voltage. The maximum possible voltage is 1.2V per cell (multiple cell in series for increased voltage). The carbon in older microphones was part of converting sound to electricity but I have no idea what the actual mechanism was.

lorenrad (author)egbertfitzwilly2009-05-29

The carbon produced a piezoelectric effect. Sound pressure on the carbon produced a voltage with an amplitude in proportion to the intensity of the sound waves impinging on it.

static (author)lorenrad2009-06-02

You are thinking of crystal microphone elements, the carbon mic element don't generate power.

buteman (author)static2010-01-28

That's right. The carbon was in the form of small granules. It was wired in series with a fixed resistor. They were fed with a fixed voltage. As it picked up sound waves the carbon compressed and relaxed in response. This varied the resistance of the carbon and so a variable voltage was generated between the junction of the fixed resistor and the carbon and ground, which of course meant it was acting as a variable resistor.

macrumpton (author)lorenrad2009-05-29

Making one of those would be a cool instructable.

static (author)egbertfitzwilly2009-06-02

My guess the internal resistance has something to do with the observed voltage drop if the individual cells arranged into a battery as compared to there open circuit voltage. have measured the voltage of the cells with a load applied?

static (author)macrumpton2009-06-02

The carbon microphone element doesn't create electricity. The element is essentially a variable resistor, that varies the current in a circuit, so information can be transmitted using DC, varying DC to be more exact

innerhealer108 (author)2015-09-18

Carbon which is used in water filters can also be used....?

Yes, I believe so.

Unsafe At Any Speed (author)2014-02-03

You have been charged with a salt and battery!

Dick Cappels (author)2009-05-28

With only 0.5 volts, you would probably only be able to get a joule thief to run if it is made with a Germanium transistor. Otherwise, you might try putting two cells in series.

Agreed. With my "Easy Carbon Electrode" I got as high as .925 mV. I'm putting together my Joule Thief this week. Will advise.


And....nothing ever happens on time or in budget....

nutsandbolts_64 (author)2010-04-26

Nice! I think Americans and Englishmen should agree on a general term that refers to an object that is spelled differently in both...... Like aluminium and aluminum and duct and duck tape. Honestly though, let's just refer to alumin(i)um to its ID in the periodic table. Back to topic of instructable, can I use homemade charcoal instead? People here don't sell charcoal briquettes (we prefer LPG). And what's the shelf-life of this battery?

Speedmite (author)2009-05-31

This looks like a fun battery. I make potatoes get 1.8 volts, which is more than pickles, onions, celery, grapefruit, a vinegar battery, lemons, and a few others. These were in pairs of halves, except the vinegar,which there was 2. But awesome, and simple. I think the activated charcoal would work better, but this does seem a little messy. I was also wondering if it smelled bad. Pickle and onion batteries stink very bad after only an hour.

Check out my Easy Carbon Electrode instructable. That's got a much, much cleaner design. No, there are no detectable odors as far as I can tell.

buteman (author)egbertfitzwilly2010-01-27

What is the conductive foam you find with computer motherboards made from and could it be used instead of the carbon?

egbertfitzwilly (author)buteman2010-01-27

I'm not familiar with a conductive foam, most electronics are packed in non-conductive materials. However I expect that any non-reactive, conductive material could work but keep in mind I'm not a scientist, I just play one on Instructables.

Actually many commerical aluminum oxide devices use metal electrodes. In my projects I use carbon to ensure that no confusion arises about the operation or results.

The al-oxide rig in Salt-Water-and-Aluminum-Foil-Night-Light/ might be a better test bed for that sort of experiment.

I would be very pleased to hear how this experiment comes out. Don't forget to put a porous non-conductive layer ( such as paper towels or something ) between the aluminum and the carbon (or foam) electrode.

buteman (author)egbertfitzwilly2010-01-28

Ok, thanks,
My wife does a lot of craft work so we often visit art and craft shops. In one I saw some perforated plastic sheet. Next time I visit the mainland I will buy some and see how that works out as the insulator.

egbertfitzwilly (author)buteman2010-01-29

silkscreen material, plastic screen or thin cloth can also be used.

buteman (author)egbertfitzwilly2010-01-30

Well that's disappointing.
I checked the black open cell foam, the semi transparent electronic items often come in and just to complete the checks also the pink closed cell foam.
All very high resistance >40Mohm over about 1/2".

egbertfitzwilly (author)buteman2010-01-31

Don't overlook the possibilities of the foam as an insulating layer in place of the sponge. Line the can with foam and fill with the charcoal, cap with the copper grid and open cell foam. Remember that oxygen needs to get to the carbon so the top should be open, maybe some cheesecloth or a single layer of the open cell.

Add some saline and you have a much tidier cell that could easily be wired in series to produce 3-6V.

cool. At first I saw 2 leads, a black and red from the carbon electrode. Then I figured out that the black was a shadow. =)

stoobers (author)Speedmite2010-01-07

The voltage is due to the reaction of the two half-cells.  One of the leads is usually copper, the other is usually zinc.  The vegetables contain the electrolyte to corrode the leads and generate the potential.

Sadly, it is not power from potatoes.  It is power from the metals reacting.  But its still fun.

static (author)2009-06-02

Your wikipedia link lead to this link IMO does a good job of explaining what's going on in a AL air battery. Appears the activated charcoal would be the better choice, but you do NOT want to crush it. Crushing it would destroys it's porosity, and permeability. Both make it the better choice, because will contain more are than powder charcoal. Reads as if adding weight will make a better performing battery. My guess is that the weight increases the conductivity of the activated charcoal. I would think your addition of the copper screening against the charcoal would make for a better performing battery. In the event you are really McGuivering it a coarser grind may prove better.For the irelavent; while Duck tape is(or can be) duct tape, not all duct tape is Duck tape. Looking foward to your other AL/air battery projects to be posted

egbertfitzwilly (author)static2009-06-03

Did you see this one Easy Carbon Electrode. Vastly improved output and significantly improved electrode.

minkette (author)2009-05-31

Possibly the sanding down of the can is required to get to a layer of 'pure' aluminium - I vaguely remember at school learning that aluminium is naturally soft and reactive, but the reason we can use it for its strength is that aluminium oxide naturally forms all around it like a protective shell and aluminium oxide is really hard.
So it's like you're cleaning the rust off _

This is just a hypothesis though, I'm no chemist!

kennyhaa (author)2009-05-26

Would it be possible to use activated carbon granules (i.e. aquarium filter carbon)? It may provide a carbon source that is more pure.

shanmugammpl (author)kennyhaa2009-05-28

yes get the charcoal tablets from the pharmacy, it is activated charcoal, powder it and use it. i tried it with aluminium foil and managed to get around 1 volt max.

What charcoal tablets from the pharmacy? Is this a dietary supplement or an aquarium filter thing?

well this isn't a dietary supplement not its not the aquarium filter as well. It is used for treatment of food poisoning. as the activated charcoal adsorbs the "poison" from your stomach and renders it safe. so just ask them for activated charcoal. it is cheap, then you just powder it.

Thank you very much for this information. I will investigate this alternative and update the instructable if it works out. What form does in come in normally? A solid chunk of carbon would also be extremely useful.

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