Battery design

[yoursoawsome]

Hello,

I am wanting to design an eco friendly battery for a science fair project. So far I know how a battery works and how to make one. I am really stuck on choosing what materials to use for the cathode, electrolyte and anode. I want the materials to be abundant, safe and eco-friendly. I was thinking carbon would make a good cathode and aluminium would make a good anode. And either citric acid,  vinegar,  salt water or Gatorade would make a good electrolyte. Any suggestions would be nice thanks.

[Paul Price]

Google it. Lots of ways to do this with citrus/potato/apple etc.




www.google.com/search?q=fruit+battery&client=firefox-a&hs=gL2&rls=org.mozilla:en-US:official&channel=fflb&tbm=isch&tbo=u&source=univ&sa=X&ei=X8_EVK3DIMTNygP51oKYCw&ved=0CC4QsAQ&biw=1280&bih=895

Just stick two different metals(nails, pins) into a orange and you've made a really funky low-power battery.

[T3sl4co1l]

Hmm, something like an iron-air battery (vinegar electrolyte, plus salt to increase conductivity?) would be pretty damn cheap to make anywhere in the world, and from nontoxic everything.  Terrible performance though (0.3-0.5V per cell!).

Aluminum offers a mess of voltage (not as much as lithium, but up there) and charge (three electrons per atom, whereas lithium only offers one), but it can't be used in water (which reacts spontaneously with metallic aluminum*).  Zinc is the highest reduction potential that can be used with water, hence its long standing popularity (alkaline and "dry" cells).

*Aluminum normally forms an oxide layer, which is your biggest obstacle.  If you defeat it (e.g., by forming a mercury amalgam -- hey, bear with me here), the self-discharge rate is huge, and you still only get to keep so much voltage (because water breaks down at 1.2V).

Magnesium metal is also pretty cheap and available (and like aluminum, certainly not toxic), and easier to build a battery with (the oxide product is easier to deal with), but still limited by water.

Tim

[LabSpokane]

If you want try something different,  but also an energy storage device, build a pumped hydro energy storage system.  Water is pretty Eco friendly. Two reservoirs, one high, one low. Use your renewable power source to fill the high reservoir with a pump. Discharge the high to low and run the pump backwards as a generator to discharge your "battery."

[yoursoawsome]

Hmm, something like an iron-air battery (vinegar electrolyte, plus salt to increase conductivity?) would be pretty damn cheap to make anywhere in the world, and from nontoxic everything.  Terrible performance though (0.3-0.5V per cell!).

Aluminum offers a mess of voltage (not as much as lithium, but up there) and charge (three electrons per atom, whereas lithium only offers one), but it can't be used in water (which reacts spontaneously with metallic aluminum*).  Zinc is the highest reduction potential that can be used with water, hence its long standing popularity (alkaline and "dry" cells).

*Aluminum normally forms an oxide layer, which is your biggest obstacle.  If you defeat it (e.g., by forming a mercury amalgam -- hey, bear with me here), the self-discharge rate is huge, and you still only get to keep so much voltage (because water breaks down at 1.2V).

Magnesium metal is also pretty cheap and available (and like aluminum, certainly not toxic), and easier to build a battery with (the oxide product is easier to deal with), but still limited by water.

Tim

What requirements do the cathode and anodes have to have?  What make one metal good and the other not as good? What characteristics do they need?
Thanks

[Refrigerator]

This one is a great example:

[mtdoc]

Build a Nickel Iron Battery aka an "Edison Battery".  More of a challenge than the potato or citrus battery though.

Here's a you tube video with more info about the history and how to make one at home:

[T3sl4co1l]

What requirements do the cathode and anodes have to have?  What make one metal good and the other not as good? What characteristics do they need?
Thanks

The first most obvious problem is not reacting with the electrolyte.  So if you want more than 1.2V from the anode, you have to use something other than water.  (Lithium cells use something weird like diethyl carbonate plus something ionic dissolved in it.)  After that, a whole mess of complex and mucky chemistry gets involved: free energy (kinetics: how fast it reacts, under various conditions), surface activity, oxidation products and how well they adhere (you need an adherent oxidation product for it to be rechargeable; lead metal forms adherent lead sulfate in the lead-acid battery, but zinc does not, hence little of the zinc hydroxide byproduct can be reversed in an alkaline cell -- and this is part of the reason why they are not rechargeable), the list goes on.

Really good batteries are hard to design because the chemistry and materials science are all very complex; they're often discovered as much by accident as by intent.  You might have some vague idea of a starting point, like, let's use lithium metal because it's got the most voltage -- and then just try a thousand variations of electrolyte, carrier, cathode and so on, and hope that you'll find something useful.

Just for playing around, the biggest drawback is internal resistance.  Yes you can put two hunks of dissimilar metal in vinegar and measure a voltage, but that doesn't mean it's useful.  To minimize resistance, and therefore maximize the amount of power that can be drawn from the cell, you need to get the electrodes as close together as possible (usually, using a soaked, permeable membrane to prevent the electrodes from shorting out!), the area as large as possible (which is why spiral wound structures are so popular, using long, thin sheets of metal for the electrodes), and the electrolyte as conductive as is practical.

Electrolyte examples:
The dry cell uses ammonium chloride, which dissolves something like 40% strength in water.  Sodium chloride saturates at 25%, and potassium chloride around 33%.
The alkaline cell uses something like 20% KOH, a strong base.
The lead-acid cell uses 20-40% sulfuric acid, as its name implies.
All of these are pretty strong (near saturation), and good ionic conductors.

In the case of sulfuric acid, both the pure substance and the solution are liquids, so any strength from 0% to 100% could be made.  But as it happens, it's most conductive (most strongly ionized) around this strength.  Sulfuric acid can give up multiple ions when it dissolves, so it can make a more conductive solution, but only when dissolved sufficiently.  This, despite being weaker in solution!

Tim

[yoursoawsome]

What requirements do the cathode and anodes have to have?  What make one metal good and the other not as good? What characteristics do they need?
Thanks

The first most obvious problem is not reacting with the electrolyte.  So if you want more than 1.2V from the anode, you have to use something other than water.  (Lithium cells use something weird like diethyl carbonate plus something ionic dissolved in it.)  After that, a whole mess of complex and mucky chemistry gets involved: free energy (kinetics: how fast it reacts, under various conditions), surface activity, oxidation products and how well they adhere (you need an adherent oxidation product for it to be rechargeable; lead metal forms adherent lead sulfate in the lead-acid battery, but zinc does not, hence little of the zinc hydroxide byproduct can be reversed in an alkaline cell -- and this is part of the reason why they are not rechargeable), the list goes on.

Really good batteries are hard to design because the chemistry and materials science are all very complex; they're often discovered as much by accident as by intent.  You might have some vague idea of a starting point, like, let's use lithium metal because it's got the most voltage -- and then just try a thousand variations of electrolyte, carrier, cathode and so on, and hope that you'll find something useful.

Just for playing around, the biggest drawback is internal resistance.  Yes you can put two hunks of dissimilar metal in vinegar and measure a voltage, but that doesn't mean it's useful.  To minimize resistance, and therefore maximize the amount of power that can be drawn from the cell, you need to get the electrodes as close together as possible (usually, using a soaked, permeable membrane to prevent the electrodes from shorting out!), the area as large as possible (which is why spiral wound structures are so popular, using long, thin sheets of metal for the electrodes), and the electrolyte as conductive as is practical.

Electrolyte examples:
The dry cell uses ammonium chloride, which dissolves something like 40% strength in water.  Sodium chloride saturates at 25%, and potassium chloride around 33%.
The alkaline cell uses something like 20% KOH, a strong base.
The lead-acid cell uses 20-40% sulfuric acid, as its name implies.
All of these are pretty strong (near saturation), and good ionic conductors.

In the case of sulfuric acid, both the pure substance and the solution are liquids, so any strength from 0% to 100% could be made.  But as it happens, it's most conductive (most strongly ionized) around this strength.  Sulfuric acid can give up multiple ions when it dissolves, so it can make a more conductive solution, but only when dissolved sufficiently.  This, despite being weaker in solution!

Tim

Thank you so much for this information! Where did you learn this? I am deciding on using aluminium as the anode and carbon as the cathode. I am hoping to use vinegar with salt for the electrolyte. Will the carbon or aluminium react with it?  will aluminium foil work? What do I have to change to make this rechargeable? I understood something about being adherent.

Thank you so much

[IanB]

Thank you so much for this information! Where did you learn this? I am deciding on using aluminium as the anode and carbon as the cathode. I am hoping to use vinegar with salt for the electrolyte. Will the carbon or aluminium react with it?  will aluminium foil work? What do I have to change to make this rechargeable? I understood something about being adherent.

Detailed information about how batteries work would be found in college level chemistry, when studying electrochemistry. There you will find terms like standard electrode potentials, reduction potentials and half-cells.

For constructing an actual working cell, it may be better to reproduce an existing known design, since this is likely to produce a more interesting amount of electricity, to light a bulb or run a motor. A place to begin might be to look at the Leclanché cell and see if you can make one of those. (Some of the parts to make one, such as zinc and manganese dioxide, can be cheaply obtained by disassembling an ordinary "super heavy duty" dry cell from a dollar store.)