Building a Battery from Molten Salt

During World War II a scientist named Georg Otto Erb developed the molten salt battery for use in military applications. The war ended before Erb’s batteries found any real use, but British Intelligence wrote a report about the technology and the United States adopted the technology for artillery fuses.

Molten salt batteries have two main advantages. First, you can store them for a long time (50 years or more) with no problems. Once the salt melts (usually from a pyrotechnic charge), the battery can produce a lot of energy for a relatively short period of time thanks to the high ionic conductivity of the electrolyte (about three times that of sulfuric acid).

[OrbitalDesigns] couldn’t find a DIY version of a molten salt battery so he decided to make one himself. Although he didn’t get the amount of power you’d find in a commercial design, it did provide 1.6V and enough power to light an LED.

The electrolyte was a mixture of potassium chloride and lithium chloride and melts at about 350 to 400 degrees Celsius. He used nickel and magnesium for electrodes. Potassium chloride is used as a salt substitute, so it isn’t dangerous to handle (at least, no more dangerous than anything else heated to 400 degrees Celsius). The lithium compound, however, is slightly toxic (even though it was briefly sold as a salt substitute, also). If you try to replicate the battery, be sure you read the MSDS for all the materials.

37 thoughts on “Building a Battery from Molten Salt

  1. Reading up on the history of these batteries, you realize that WWII wartime innovation spawned some of the greatest ideas in the history of mankind, culminating with the atom bomb and the moon missions. Now we use science to build machines to play candy crush. Progress!

    1. You do understand that we’re facing a totally unprecedented technical challenge the size we haven’t seen since the industrial revolution, and we don’t have the advantage of untapped natural resources on the material side of it?

      Renewable energy such as solar PV or wind power generate the majority of their output energy during a minority of the operating hours; solar power at roughly 1/10th of the time and wind power roughly 1:5th of the time. The end result is that these energy sources combined in roughly equal measures have a peak-to-average power ratio around 7:1

      So, even in a fairly large grid that consists of a high portion of these renewable sources, during a regular day one can expect to either have a severe power shortfall or a massive glut of overproduction, because the chances that you get just enough power to power everything is practically nil, and the situation can change in a matter of two hours.

      That’s why batteries become absolutely essential. The US electrical power generation is about 500 GW at any given time, give or take depending on the time of day, which means there’s a need for 12 TWh of batteries to have one single day of buffer between the source and the load – and mind you, we might get a week-long lull in output very easily: 14% deficit over 7 days is the same as one full day with no output, so without the batteries it’s back to shoveling coal.

      How much is 12 TWh? The Tesla Gigafactory can crank out 35 GWh worth of batteries per year and will increase the worldwide demand for lithium by a fifth. Given a modest shelf/operating life for the batteries at 10 years per cell, we would need 34 Tesla Gigafactories in the US just cranking out spare batteries for the giant grid UPS that’s keeping our lights on when the wind isn’t blowing. As a result, the worldwide demand for lithium would increase by a factor of six. Taken worldwide, the problem is 20 times worse still because other countries need renewable power, so they too need batteries.

      That’s what our scientists are working to solve. The machines that play Candy Crush are just the side effect – means to fund it all – since our governments and people have completely misplaced their effort and stuck their heads too far up their collective asses to realize what a huge mission we’ve got just to survive the next 100 years as a culture and possibly as a species.

          1. More specifically, electricity use is only the tip of the iceberg which everyone is refusing to see.

            Ordinary household energy consumption is between 20-50% electricity, and nearly all of the rest comes from natural gas and fuel oil used for hot water, cooking, space heating. In some regions, district heating and sometimes cooling is used for efficiency, but there again the power comes from fossil fuels because they’re many times cheaper. Then there’s the car and the commute to work, and the power used at work etc. etc.

            Overall, only about a fifth of the energy we use is in the form of electricity, and despite efforts in efficiency and cutting off waste, the transition towards renewable energy will have to see electricity consumption increase – not decrease.

            Natural gas from a pipeline in California for example costs the distribution utility about 1.6 cents a kWh. In Germany, coal costs about $60 a ton or 0.9 cents a kWh. Both of these places are “spearheading” the renewable future, when in actuality they’re just shifting loads off the electric grid and powering them directly with fossil fuels because it’s becoming too costly otherwise.

          1. That’s a bit of a red herring; you need more energy to build a battery than it stores, too. It’s not like you can only use a dam once, then throw it away.

        1. Okay, I’ll talk about population control: It’s largely irrelevant, because developed countries have negligible or negative growth; world population is expected to peak around 2050.

  2. Don Sadoway’s group over at MIT is researching liquid electrolyte batteries with many of the same characteristics. They use electrodes of molten metal (such as lithium and lead), and an electrolyte of molten salt in the middle.

    The proposed use is for energy storage at point of generation: if your wind farm is generating at times when there is no demand for it, you can charge these batteries for later release into the grid when it’s needed.

    Any inefficiencies go into keeping the electrodes and electrolytes molten, and good thermal insulation isn’t hard to build. The batteries stay molten for a long time.

      1. This is something that also concerns me. When I hear molten anything and battery in the same sentence I cringe. The amount of energy to heat up the battery must by heavily outweighed by the described short but powerful output. Otherwise at this point the thermal energy alone would provide energy to run a steam engine generator or a Stirling engine.

        1. Dr. Sadoway’s battery is a storage battery.

          Liquid Magnesium and Antimony act as the electrodes, and their density is such that the Magnesium sinks and Antimony floats. In between these is the molten salt layer containing Antimony and Magnesium.

          Charging the battery pulls Magnesium from the salt mixture as molten metal, which floats to the top. Antimony is consumed and replaces the Magnesium in the salt layer.

          Discharging, Magnesium is electrochemically deposited into the salt layer, releasing Antimony which sinks to the bottom.

          Using density to separate the electrodes is an interesting innovation. Also, since the electrodes are continuously formed and reformed, they don’t degrade like solid electrodes.

          Here’s a brief article explaining the mechanism of the battery:

  3. Development of these batteries solved a critical issue with nuclear weapons. Previously they had to be left open so that a fresh cell battery could be inserted and sealed prior to being loaded onto a plane; batteries at the time had such short shelf lives the weapons couldn’t be manufactured with them included.

    Molen salt batteries and their high power density and long shelf life allowed the weapons to be developed “sealed pit” and never opened, since the battery was ready to go as soon as the incendiary charge was set off to melt the electrode.

      1. You’re right. I thought the battery advance was what was required to make a sealed pit weapon, but it turns out they were two separate advances, both required in order to be able to keep the warhead itself permanently shut.

        1. Actually this is a much bigger deal for missiles than nuclear warheads. The battery for a missile only needs to work for the flight time of the missile but a missile might be stored for years before it is used. It really does not matter if you are talking about an ICBM or a small anti-tank missile.
          BTW nuclear warheads are still not completely sealed because they often use Tritium and that has a pretty short half life and decays to He3 which is a fission poison.

  4. Do you know DES (deep eutectic solvent) and/or ionic liquids?
    Basically are molten salt at room temperature.
    Many researchers are working on that and they could change the world of batteries.
    That based on chloride, move chloride ion between two metals, one more electropositive than other.

    Also, take look to this to Akuto photorechargeable batteries: they can transform light into electrochemical energy and store it using…. hydrogen from water.

  5. In one of the longer MIT videos, he mentions that once up to temperature and in either a state of charge or discharge, a fair amount of heat is generated by the ion movement, sufficient that with decent insulation the battery will maintain its molten state on its own. An external source of heat would only be necessary to get it started. And since the “charge” is stored in the form of physically stable ions, yes it will hold a charge for a long time when cold. The charge/discharge cycles they observed had approximately a 70% efficiency, most of the loss probably being in the form of heat. This compares to pump-hydro (one of the most efficient competitors) at about 60% and hydraulic hydro at about 40%. Consumer grade lead acid batteries with an inverter/charger run about 40% efficiency.

    So yes, the idea of using molten metal/salt as a battery is radical and not likely to catch on for pocket devices. It’s probably ONLY feasible on a massive scale, but then that was the entire intention of the development. His hope isn’t to store a couple days of energy for an off-grid survivalist’s house. His hope is to store a couple months energy for a major city…

    1. Hi I have build a molten battery with a solar panel, plate heat exchanger and Grundfos water ss pump to heat a pool.
      No need to produce a high voltage just the led lined ss box with a flow and Return. I have 2 port valves for heating and water cylinder.

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