Two phase electrolytes used as halogen traps in metal halogen secondary cells and batteries

#This invention relates to water insoluble organic electrolytes useful for complexing halogens and more particularly to two-phase electrolytes useful as an electrolyte for electrochemical cells and batteries of the type which utilize a halogen as its electrochemically active agent.

#Voltaic cells which include an aqueous solution of zinc or cadmium halide as an electrolyte are known, but are frequently characterized by a relatively high self-discharge rate, low capacity, and high internal resistance. Since elemental halogen is soluble in the aqueous electrolyte, it is difficult to keep metallic zinc or cadmium and elemental halogen apart while simultaneously achieving a system in which a good percentage of the theoretical energy storage capacity can be realized.

#Recently, various attempts have been made to prevent elemental halogen from migrating to the zinc or cadmium electrode. For example, U.S. Pat. No. 3,352,720 to G. R. Wilson et al teaches the use of water insoluble polymeric amine halogen complexes in place of the elemental halogen. While the structures disclosed in the Wilson et al patent function as halogen cells, they nevertheless suffer from less than optimum capacities and self-discharge rates because of the low stability of the polyhalogens employed.

#FIG. 1 is a cross-sectional view of a cell of the type in which the complexing electrolytes of the present invention are useful;

#FIG. 2 is a graph which illustrates ionic conductivities;

#FIG. 3 is a schematic of a regenerative fuel cell in which a recirculating electrolyte of the present invention is useful; and,

#At the outset, it is desirable to comment on certain terms that are used throughout this specification and claims. For example, the terms "zinc electrode" and "bromide electrode" are not intended to imply that the electrodes are formed from these material exclusively. As is conventional practice, the terms are used merely to indicate the electrochemically active element reacting. The metal and halogen electrodes of the cells with which the electrolytes of the present invention are employed, are electrically conductive, and preferably porous and noncorrosive. Carbon in its various forms is a preferred material. The carbon of the metal electrode serves as a plating surface for zinc or cadmium.

#Furthermore, although reference is made to one counter electrode and one metal electrode, it is obvious that the compounds of the invention are useful in cells which include more than one pair of electrodes and with batteries of two or more cells constructed in accordance with methods known to those skilled in the art. Because cadmium is electrochemically similar to zinc, it is also obvious that the zinc of the electrode and the electrolyte can be replaced by cadmium. Although bromine is used throughout this specification and claims, it will be apparent to those skilled in the art that chlorine, iodine, or any combination of bromine, chlorine, and iodine may be substituted therefore.

#During discharge of the well-known zinc bromine cell the following half reactions occur: