Thermite is chemically powerful. It stores immense energy with very common materials, namely aluminum metal and iron oxide. The oxide provides the oxygen to the aluminum which enables the reaction to run extremely hot without requiring external air, so it will work underwater or in a closed space if need be. This mostly gets used in military applications, but there's a few industrial applications where it can be used for welding or demolitions. There's even a type of welding that uses explosives to mechanically join thick plates of steel by bashing them together. I spent two years learning welding, and I learned some metallurgy in the process.
The limitation of thermite is the process only goes one way. And its very hot, an out of control reaction you start, then run away while it consumes its materials until the oxidation is finished. The US military uses slabs of aluminum to power their emergency radios for nuclear bomb launches, which makes a really weird noise btw. The radios, I mean. Not the bombs. Aluminum used like this oxidizes in the air, turning into powder, into dust. It falls off exposing more to the air to oxidize and releases electricity in the process. And lots of heat. But its very reliable and requires no external power source beyond a battery to start it going. You can't reverse this process because you can't pull the oxygen off the aluminum metal. Which is a real shame.
I'd been pondering this question since shortly after learning just how few types of rechargeable batteries there are. And learning that most sit in either acid baths or brines. Acids allow for easy exchange of hydrogen and hydroxide ions with metals via anode and cathode, so you can add or remove electricity very methodically, and those batteries stop working when they dry out. This is why you can often fix a bad battery that stops working after you overheat your engine by popping the top and adding some bottled water till it fills back up. Recharge and boom, it works again. Had this happen when someone who should have known better did that, and saved myself about $140 with a $1 bottle of water. Just like that.
I have to wonder of the aluminum electrolysis reaction will work in water, and if it requires either acid or a salt-brine of some kind to catalyze the reaction. Buffer it down so it won't overheat, won't run away and melt what its been put into, won't tear the water into hydrogen gas and explode, and will allow you to put electricity back into it to return it to metal, and charge it back up. In essence, what combination will turn thermite from a burning explosive into a battery. A battery with materials so common everybody on earth could have a vehicle powered by this, and have plenty of those materials left over. As it happens, Iron and Aluminum are extremely common elements. You find them in most soils. Clay is aluminum oxide with some silicates and other stuff, but pure clay, used to make electronics is also the raw materials for sapphire and ruby. And still aluminum oxide. Aluminum 2, Oxygen 5. Strip out the oxygen using electricity and you get aluminum metal. Its that stripping which needs to be reversible and done on demand without overheating. That's your battery.
The energy density, depending on the buffering efficiency, is still better than lithium, so you'd need something like 1/3 as much battery pack to get the same amount of useful power as a lithium battery. If the buffering catalyst is stronger, the battery runs cooler but needs more bulk for accessible power. I think we do need to accept that batteries need cooling. Heat sinks. And possibly heaters. Their chemical reactions do release heat. Not as noisy or noticeable as an internal combustion car engine, but heat just the same.
I hope that somebody is doing these experiments, methodically trying to find a catalyst that works for aluminum oxide. There's really no real need for iron in this equation, just a source of oxygen to react with the aluminum metal and back again. If I had a chemistry lab, I'd do it myself. Probably starting with reading up on physical chemistry so I can understand what's going on, then run some simulations, and test the likely ones to see if they actually match or if the data in them is wrong.
If a military had discovered this trick, they'd likely keep it secret for an advantage, though at this point, we're looking at interstate genocide using fracking, causing cancer, earthquakes, and eventually killing millions for those last drops of expensive oil. Isn't a super-battery a better strategic move that saves lives and prevents wars, and lets us leave the oil in the ground? And our water untainted? This is why I hope the solution isn't already discovered. Ignorance is better than sadism.
Other than electric cars, and electric buses, you could also use these batteries for electric delivery vehicles, for electric bicycles much lighter than current ones, since it would fit inside the frame, and new computer batteries for laptops and cellphones which should last all day or week on a charge, and no charge memory. It's not lithium or cadmium.
The brine solution might be something as simple as boron in water, which readily breaks apart into ions and would transport well, but doesn't generally bond with aluminum so should allow it to be a two way reaction instead of forming a new boron-aluminum mineral, something we try to avoid with a battery. Boron is the active part in borax soap. Another option would be sodium, from table salt. Sodium chloride might work well with aluminum, but I'd probably want to research any minerals those form. If there's a mineral, then its a stable outcome, which would cause the reaction to stop working as the crystal grows, meaning it would stop being a battery and "wear out" eventually. Not a desired outcome. A professional chemist, one not completely bound by their own narcissism (I have worked with professional chemists for years, and yes, that's a serious character flaw of that field), might know some shortcuts, or be willing to mathematically examine it. Electronics is all about the weird tweaks of chemistry, after all.
Maybe there's some tweak for this century's equivalent of the incandescent lightbulb filament? Only this time, it saves a billion lives. That's what electric vehicles could do, best case. Electric tractors to grow food, remember. When the oil runs out, we lose a lot of food production. And algae that makes diesel fuel is just asking to fill out drinking water and oceans with fire. Not a bright idea. This is safer. This is less destructive. This would save more lives.
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