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Automotive
- Nov 24, 2024
- 1
I've been reading into metal air batteries lately and I found them quite interesting, particularly Al-air and Li-air batteries. I found that a big issue in metal air batteries is the self corrosion of the metal anode due to water in the electrolyte reacting with the metal and cathode clogging due to byproducts of the reaction. I've been reading up on strategies to mitigate the self corrosion and I found a few interesting techniques.
I had some ideas myself on how to mitigate the self corrosion issue and I've been thinking about building a small model at home to test them out. However, I'm not sure if these ideas are practically sound and how I would be able to test them out at home, so any insight would be great.
My first idea would be to make an metal air battery using a regular alkaline electrolyte like KOH or NaOH but with additional steps to decrease self corrosion. Some methods that are being tested currently are alloying the metal with other materials to increase hydrogen overpotential or putting in additives (such as ZnO here and here) into the electrolyte to inhibit the self corrosion reaction.
An idea I had to inhibit the self corrosion while the battery is not in use to utilize an metal strip feed, where the metal itself is fed through the electrolyte from a roll which is situated outside the battery. The metal would oxidize as it is fed through the electrolyte and exit into a waste tank. This way the metal does not react with the electrolyte when the battery is not in use. The strip could be fed in on a carrier or be mounted on a binder to ensure that the oxide power does not disintegrate and enter into the electrolyte. Another possible method would be to feed in aluminum powder which is bound onto a sticky strip (like fly paper).
To inhibit the self corrosion, an possible solution would be to add a microporous mesh made of an inert material inside the electrolyte in contact with the metal feed on both sides. The mesh would maintain a small negative charge (just enough to inhibit the self corrosion without drawing too much energy) to induce the metal ions to separate from the metal into the electrolyte and repel the electrons from the water molecules. The metal roll would be mounted to a conductive material which would carry the electrons out through the circuit. Where the electrical contacts are located, there would be a slight positive charged maintained on a non conductive material which is in electrical contact with the roll. This would draw the electrons to separate from the metal and go into the circuit. Overall, this method should inhibit the reaction with the water molecules as there is additional incentive for the metal ions to dissolve in the solution vs reacting with the water molecules.
The idea is to use some or all of these methods to inhibit the self corrosion of the anode. The aluminum fuel could just be quick swapped by replacing the roll and no further maintenance is required when refueling.
Another idea is to use a non aqueous electrolyte as these tend to react less with the metal. From what I've been able to find out, solid state electrolytes are generally non reactive but have low ionic conductivity so I wouldn't want to use one of those. Ionic liquids are non reactive and have some good properties but have low conductivity (compared to alkaline electrolytes, still higher than solid state) due to high viscosity, and high cost due to low manufacturing. (here)
An idea would be to add inert liquids to the ionic liquid to form a mixture and increase the viscosity without affecting the chemical properties. Or, possibly to mechanically swirl the mixture so that the ion transport is faster.
Another non-aqueous electrolyte that could be used is an ammonia-based electrolyte. Ammonia is a good solvent so it should be able to conduct an ionic current and is quite non reactive towards most metals. It does have a low boiling point (-30c) but this could possibly be solved by adding solvents to increase boiling point or lowering the temperature in the battery.
For Li-air batteries, an idea I had to prevent cathode clogging would be to build a cylinder shaped cathode that would rotate out of the electrolyte into a solution like KOH which would dissolve the lithium peroxide. The cathode would then rotate out of the electrolyte into open air where it would dry, then be submerged in the electrolyte again, so there would be a third of the cathode at any given time submerged in the electrolyte. The 3 separate sections would be electrically isolated to prevent the dissolution process from interfering with the battery current.
I had some ideas myself on how to mitigate the self corrosion issue and I've been thinking about building a small model at home to test them out. However, I'm not sure if these ideas are practically sound and how I would be able to test them out at home, so any insight would be great.
My first idea would be to make an metal air battery using a regular alkaline electrolyte like KOH or NaOH but with additional steps to decrease self corrosion. Some methods that are being tested currently are alloying the metal with other materials to increase hydrogen overpotential or putting in additives (such as ZnO here and here) into the electrolyte to inhibit the self corrosion reaction.
An idea I had to inhibit the self corrosion while the battery is not in use to utilize an metal strip feed, where the metal itself is fed through the electrolyte from a roll which is situated outside the battery. The metal would oxidize as it is fed through the electrolyte and exit into a waste tank. This way the metal does not react with the electrolyte when the battery is not in use. The strip could be fed in on a carrier or be mounted on a binder to ensure that the oxide power does not disintegrate and enter into the electrolyte. Another possible method would be to feed in aluminum powder which is bound onto a sticky strip (like fly paper).
To inhibit the self corrosion, an possible solution would be to add a microporous mesh made of an inert material inside the electrolyte in contact with the metal feed on both sides. The mesh would maintain a small negative charge (just enough to inhibit the self corrosion without drawing too much energy) to induce the metal ions to separate from the metal into the electrolyte and repel the electrons from the water molecules. The metal roll would be mounted to a conductive material which would carry the electrons out through the circuit. Where the electrical contacts are located, there would be a slight positive charged maintained on a non conductive material which is in electrical contact with the roll. This would draw the electrons to separate from the metal and go into the circuit. Overall, this method should inhibit the reaction with the water molecules as there is additional incentive for the metal ions to dissolve in the solution vs reacting with the water molecules.
The idea is to use some or all of these methods to inhibit the self corrosion of the anode. The aluminum fuel could just be quick swapped by replacing the roll and no further maintenance is required when refueling.
Another idea is to use a non aqueous electrolyte as these tend to react less with the metal. From what I've been able to find out, solid state electrolytes are generally non reactive but have low ionic conductivity so I wouldn't want to use one of those. Ionic liquids are non reactive and have some good properties but have low conductivity (compared to alkaline electrolytes, still higher than solid state) due to high viscosity, and high cost due to low manufacturing. (here)
An idea would be to add inert liquids to the ionic liquid to form a mixture and increase the viscosity without affecting the chemical properties. Or, possibly to mechanically swirl the mixture so that the ion transport is faster.
Another non-aqueous electrolyte that could be used is an ammonia-based electrolyte. Ammonia is a good solvent so it should be able to conduct an ionic current and is quite non reactive towards most metals. It does have a low boiling point (-30c) but this could possibly be solved by adding solvents to increase boiling point or lowering the temperature in the battery.
For Li-air batteries, an idea I had to prevent cathode clogging would be to build a cylinder shaped cathode that would rotate out of the electrolyte into a solution like KOH which would dissolve the lithium peroxide. The cathode would then rotate out of the electrolyte into open air where it would dry, then be submerged in the electrolyte again, so there would be a third of the cathode at any given time submerged in the electrolyte. The 3 separate sections would be electrically isolated to prevent the dissolution process from interfering with the battery current.
