This invention relates generally to batteries and more particularly to methods of activating molten salt electrolyte batteries.
A molten salt electrolyte battery is activated by transforming the electrolyte from its non-conductive solid state to its generally highly conductive molten state, where the conduction is in the form of anion and cation migration. To activate the battery, heat must be provided to melt and heat the electrolyte to the operating temperature of the battery. Further, depending on the particular battery, additional heat must be provided for heating other parts of the battery as well as for compensating for heat losses.
One approach to heating the electrolyte is the use of an external heating source, for example electrical heating elements. However, external heating means are more expensive, complex heavy and bulky than self-contained chemical starters.
Another approach is to use chemical combustion charges which melt the solid electrolyte. However, most of these chemicals (e.g. iron-potassium perchlorate) require a shock to a percussion cap or an electric spark to cause ignition.
Attempts have been made to eliminate the need for a spark or percussion cap. One method attempted was to cause the melting of the electrolyte by contacting chlorine with a mixture of the solid electrolyte and powdered lithium metal, but it was found that the reaction between chlorine and powdered lithium is not self sustaining at room temperature because of the formation of a protective layer of lithium chloride on the surfaces of the lithium particles. Moreover, while the addition of a potassium powder initiator apparently resulted in a more complete start-up reaction, the results were not sufficiently reproducible to demonstrate the practicability of that method. Further, the potassium had the disadvantage of not completely reacting with chlorine gas until the metal was at or above its melting point (60.3.degree. C). C.). SUMMARY OF THE INVENTION
Accordingly, one objective of this invention is to provide a means for activating a battery.
Another objective of this invention is to provide a self-contained activating means for a molten salt electrolyte alkali metal-halogen gas battery.
A further object of this invention is to eliminate the need for external heating sources to melt and heat the solid alkali halide electrolyte in alkali metal-halogen gas batteries.
Still another object of this invention is to melt the electrolyte of a battery and heat it and other parts of the battery to the operating temperature of the battery.
Yet another object of the invention is to provide a combustible composition for melting and heating solid electrolytes that can be ignited without the use of a percussion cap or a spark.
Yet a further object of this invention is to provide an ignition mixture which reacts spontaneously with chlorine gas at low temperature (0.degree. C.).
A still further object of this invention is to provide an ignition mixture which reacts completely with chlorine gas at low temperatures (0.degree. C.).
Still another object of this invention is to provide combustible materials which produce waste products which are compatible with the electrolyte.
These and other objects of this invention are accomplished by providing a method comprising placing a powdered alkali metal carbide selected from the group consisting of lithium carbide, sodium carbide, potassium carbide, rubidium carbide, cesium carbide and mixtures thereof into contact with the solid alkali halide electrolyte and then contacting the alkali metal carbide with a halogen gas selected from the group consisting of fluorine, chlorine, and mixtures thereof.