Thermal Battery Technology employs inorganic salt electrolytes. The working principle and applications of different types of thermal batteries (Thermocouple and AMTEC) are explained. The inorganic salt electrolytes are relatively non-conductive solids at ambient temperatures. Integral to the thermal battery are pyrotechnic materials scaled to supply sufficient thermal energy to melt the electrolyte.

Types of Thermal Battery

We can classify a thermal battery (direct conversion) in two main types. They are:

  • Thermo-couple converter, and
  • Alkali Metal Thermal Electric Converter (AMTEC)

Thermocouple Battery

Thermo-couple Battery works on the principle of Seebeck effect. Seebeck effect says that when two different electrical conductors or semiconductors in a close circuit are kept at different temperature, then a potential difference generates between them.

Image of Thermo-couple battery

Fig.1 – Image of Thermocouple thermal battery

Keeping this phenomena in mind, electricity is generated between two electrodes in a close circuit by physically heating one electrode and keeping the other electrode cool. this method has been in use from end 19th century to store electrical energy in the form of heat energy. Now a days this method is also being used for generating emergency supply for low power applications.

This method is surely not as energy efficient as chemical batteries or capacitors, yet they are very resourceful in remote locations where energy efficient batteries or capacitors cannot be installed / unavailable.

You can still see Modern gas powered batteries which works on this Seebeck effect in today’s world.  They have a large temperature operating range and are mostly used with solar /wind powered applications in order to facilitate emergency supply during dark/windless time. Don’t be surprised if I say that this type of thermal battery is also being used in spacecrafts.

Alkali Metal Thermal Electric Converter (AMTEC Thermal Battery)

An Alkali Metal Thermal Electric Converter (AMTEC Thermal battery) is an electro-chemical Thermal battery which works on the principle of  Electro-chemical heat engine. It uses a high temperature recirculating alkali metal (Na / K) vapor acting as a fluid which passes through a solid porous electrolyte in a close circuit.  This solid electrolyte separates the electrons from the ions which then can be used to provide electricity.

how an AMTEC battery works

Fig. 2 – how an AMTEC battery works


The efficiency of AMTEC batteries in terms of energy conversion is four times to Thermo-couple batteries.

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