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Author Topic: Help needed on designing a battery  (Read 1035 times)

Offline luckp

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Help needed on designing a battery
« on: 05/04/2016 05:22:49 »
I need help with designing a battery that I'll be making for a class project and I would love to hear thoughts/ideas/feedback. It's sort of a competition between classmates, as there are bonus points that will be awarded based on certain criteria that are met.

Some of these bonus point criteria are:
weighs less than 15 grams
produces 1.5v
produces 2.5v
produces 40mA
produces 300mA
powers a small lightbulb for 30 seconds
powers a small fan for 30 seconds
powers a small motor for 30 seconds
powers a larger motor for 30 seconds
highest power to size ratio in class

I dont necessarily have to get all of those (though it would be nice too if possible!), but I'd like to maximize getting the most as possible!

We will have free access to most of the materials in the lab (copper, magnesium, zinc, NaOH, HCL, NaCl, lead, graphite, ect ect), and we can also buy just about any items from the store to use as well.

It has to be relatively safe to handle, doesn't leak when handled, and nothing extremely dangerous to mess with. ie Fluorine, Cyanide, ect. Lithium is borderline and I think it would be to reactive to safely use. I have access to Silver and other metals, as well as a couple weeks to order anything else I might need.



So this is what my idea is:

Since the first type of battery was a Voltaic pile using stacked coins, I thought I might improve and expand on that concept/idea and make something similar but more efficient. I'll make a Voltaic pile type battery using thin pieces of Magnesium foil alternating with Copper foil in round pieces like the size of a coin stacked together, with a piece of filter paper soaked in NaCl separating the metals. I would repeat this until i have several "cells" stacked high to have enough power. My reasoning behind using this is that foil is thin, so it is very lightweight and maximizes the surface area, thus maximizing the mA output potential. From my calculations, the reaction between Magnesium and Copper is fairly good and should produce a decent amount of voltage, and a strong NaCl as the electrolyte should be a good medium for this reaction to take place. The filter paper will only be damp, thus preventing leakage, and all the materials are relatively safe to handle.

Any thoughts behind this? Would there be a better electrolyte to use? Better combination of metals that might be more efficient? I'd love to hear any thoughts/input/advice!

Thanks


 

Offline chiralSPO

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Re: Help needed on designing a battery
« Reply #1 on: 05/04/2016 14:08:44 »
Sounds like you're on the right track!

Alternating magnesium and silver foils would give a greater voltage, but copper is a lot cheaper, and increasing the  the height of the stack will have a greater effect on the voltage (using Mg or Al and Cu or Ag, you won't need many cells to get well over the 2.5 V mark). To up the amperage you must increase the surface area of each cell, and/or increase the conductivity of the electrolyte. NaCl is a good choice, but you might be able to up it a little bit by using KI...

For a high power density, it might be better to use aluminum foil (likely easier to get a larger area of this than Mg foil). Also, although the reduction potential of aluminum is significantly lower than Mg, it can transfer 3 electrons per atom vs Mg's 2 electrons per atom (if coupled with Cu, the theoretical voltage of a single cell drops from 2.72 V to 2.00 V, so the overall power density goes up slightly).

Good luck!
 

Offline luckp

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Re: Help needed on designing a battery
« Reply #2 on: 05/04/2016 17:56:16 »
Thanks for the reply! I will get some KI for the electrolyte. Unfortunately I wasn't able to find any silver foil. But I did find .05mm and .1mm and .5mm thick magnesium foil as well as copper. What thickness would be the best? Thinner the better or will .05mm be too thin to hold up? I thought about using aluminum but I heard it oxidizes very fast and people tend to not get good results using it, what's your thought?

Also for surface area, discs about the size of a quarter wide enough to get enough amps? And maybe go 10 cells stacked high? Or should I focus on making the discs wider....Or would I be better off splitting into two small battery's and connecting parallel to get the amps?

So many options haha
 

Offline chiralSPO

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Re: Help needed on designing a battery
« Reply #3 on: 05/04/2016 18:33:14 »
I don't think the thickness of the metal foil will have too much influence on the amperage (copper metal will be the least resistive part of the whole cell, and the magnesium will be the next least resistive). The thicker the magnesium foil is, the longer the battery will last.

If you have access to magnesium foil, that will probably be best.

Theoretically, magnesium and copper should get you above the 2.5 V mark by a few hundred mV with just a single cell (I don't know how much you stand to lose from internal resistance). If you can get this potential with a single cell, then I guess you should focus on increasing the surface area of the electrodes (equivalent to having multiple cells in parallel). How large (width length) are your available foils? If they are large enough, it might work well just to make a 5-layered sandwich:

insulating layer (waxpaper or saran wrap etc.)
copper foil with a wire attached
paper (filter paper, paper towel, kimwipe etc.) soaked in electrolyte solution
magnesium foil with a wire attached
insulating layer (waxpaper or saran wrap etc.)

Then, roll the whole thing up and put it in a water-tight tube (or ziploc baggie) and voila!

I recommend experimenting with multiple setups to see which works best before submitting the final project.

I hope I have helped, but I can't give it all to you--both for academic integrity reasons, and because you will have to optimize  experimentally anyway to get the best result.

Good luck!
 

Offline luckp

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Re: Help needed on designing a battery
« Reply #4 on: 05/04/2016 20:46:39 »
Yes thanks so much for your input. I will most likely only be able to get 1 sheet of 115mm X 500mm for the Magnesium foil. Hopefully that's enough haha

Could you explain anymore about the use of wax paper/seran wrap for an insulator. What is the purpose of the insulator? To keep things seperated? Or to catch fluid that might leak or something? I hadn't thought about that part.

Thanks again!
 

Offline chiralSPO

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Re: Help needed on designing a battery
« Reply #5 on: 05/04/2016 21:24:38 »
When the battery is rolled up without insulation the anode and cathode would come into contact, resulting in a short circuit. Adding one layer of insulation would prevent that (and two will make it easier to wrap up, and less likely to fail without adding too much mass). See attached.
 
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Offline luckp

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Re: Help needed on designing a battery
« Reply #6 on: 10/04/2016 01:50:57 »
Any chance you could explain a little bit about why KI would be a better electrolyte to use than NaCl. I understand the purpose of needing a strong electrolyte, but I get confused when it comes to the differences between using different electrolytes. What makes one salt electrolyte better or worse than another? What more does KI contribute than NaCl does. There doesn't seem to be much information concerning electrolytes readily available on the internet.

From my calculations NaCl gives E = -4.07 and KI gives E = -3.46. Is the reason KI is slightly better is that the E value for KI is less negative than that of NaCl?

Thanks again!
 

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Re: Help needed on designing a battery
« Reply #6 on: 10/04/2016 01:50:57 »

 

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