A molten salt cell is a kind primary or secondary battery with a molten salt electrolyte, running at several hundred degrees C.
Mostly used by the military for their near-infinite shelf life due to no self discharge in the cold, frozen state near room temperature.
They can be sitting in a warehouse for decades, then be plugged into the weapon system, heated up by the included pyrotechnic charge, and provide full power and capacity.
I found the concept rather curious, but couldn't find much details or any previous DIY attempts, so i decided to make my own.
Best viewed in 1080p.
The ingredients are:
-KCl, LiCl salts to make the electrolyte
-Magnesium for one electrode
-Nickel for the other
Both LiCl and KCl have melting points over 600*C, but their mixture melts at a lower temperature.
The eutectic point is at around 60:40 molar ratio, giving 350*C.
In terms of weight, that's 1.26 gram of KCl per each gram of LiCl.
The melt is a clear liquid without any smell.
KCl is harmless and even edible, LiCl is slightly toxic.
Still, it's better not to do this in an unventilated space.
A quick proof of concept gives 1.6V open circuit for the fresh cell.
A more permanent setup finds the cell being able to power a green LED over a joule thief step-up converter.
A white LED does not run that well.
There were some bubbles in the electrolyte when shorted, but in the end it just turned gray-ish.
Once solid, the electrodes produce essentially no voltage.
With electrodes sticking in the liquid i get 20mA of short circuit current.
With a flat cell from the video i get 150mA.
Such cells are known for their high power density (amps given per cell size), achieving which will probably require a little bit of careful engineering and maybe some of the less safe chemicals.
In any case, it is a battery that works at 400-500*C, which curiously enough is the kind of temperature you can find on the surface of Venus.
If that's where we happened to live, that might have been the chemistry in our everyday AA cells, while the alkaline batteries were just some obscure cryogenic cell a few scientists heard about.
A fun what-if to consider.