Electrolyte for lithium-sulfur dioxide electrochemical cell

DETAILED DESCRIPTION OF THE INVENTION We have found that the presence of chemically uncombined aluminum chloride in the electrolyte of a lithium-sulfur dioxide electrochemical cell serves to improve the discharge capacity of the cell.
In addition, the aluminum chloride also serves to improve the cycling characteristics of rechargeable lithium-sulfur dioxide electrochemical cells.
The aluminum chloride of this invention can, of course, be solvated by the electrolyte solvent or solvents.
However, it is otherwise chemically uncombined and refers to that aluminum chloride which is in excess of any that may react chemically with any other materials that are used in preparation of the electrolyte or are introduced into the electrolyte.
For example, lithium chloride (LiCl) reacts with aluminum chloride (AlCl.
sub.
3) to yield lithium tetrachloroaluminate (LiAlCl.
sub.
4), a lithium salt.
With reference to an electrolyte prepared by dissolving lithium chloride and aluminum chloride in a suitable solvent system, the aluminum chloride of this invention refers to that material which is in excess of the amount consumed by chemical reaction with the lithium chloride.
In addition to aluminum chloride, the electrolyte used in the practice of this invention additionally comprises at least one lithium salt.
This salt serves to improve the conductivity of the electrolyte.
In addition, a high lithium cation (Li.
sup.
+) concentration in the electrolyte is highly desirable since this is believed to promote the formation of a pasivating film of lithium dithionite on the lithium anode.
Further, this lithium salt serves as a source of lithium for electrodeposition.
Suitable lithium salts for use in the practice of this invention include all lithium salts which are soluble in the electrolyte system.
For example, the electrolyte of this invention can be prepared by combining a lithium salt such as lithium chloride, lithium dithionite or lithium trifluoromethanesulfonate with aluminum chloride in a suitable solvent system