In view of the growing interest in high-temperature storage batteries, there arises an urgent demand for investigations of new chemical materials capable of satisfying the needs of modern technology.One such promising material is the CuCl-CuCl 2 salt melt that can be used as cathodic material in high-temperature chemical current sources (HTCCS). Earlier we have established that such a system in the temperature range 800-1000 K and at a pressure P C 1 2 = one bar, possesses an electronic conductivity 2.5 to 3 times the ionic.This property, together with good thermodynamic characteristics of the system, gives promise that the power characteristics of HTCCS can be increased considerably.In the course of any current-producing reaction, for example, in lithium or sodium HTCCS:In the cathodic half-cell there accumulates a component not participating in the electron transfer of lithium or sodium chloride. This changes the electrochemical and physiochemical properties of the melt.The purpose of this investigation was the measurement of density, ratio of concentrations of mono- and divalent copper, electrical conductivity and electron transfer numbers of the CuCl-CuCl 2 ionic-electronic salt melt, diluted with lithium chloride or sodium chloride (0 to 90 mole%), over the range T = 750-1000 K and at P c 1 2 = one bar. We have used an original technique of ours, based on the non-correspondence of current output to Faraday's law, to measure electron transfer numbers. Electrical conductivity was measured using the standard capillary method and a cell with a known constant.The ratio of concentrations of monovalent and bivalent copper was determined by chemical analysis of specimens selected by the quick quenching method. Density was measured by the dilatometric method.The electronic and ionic components of electrical conductivity were calculated using experimental data.The results show that the introduction of the lithium or sodium chloride into the CuCl-CuCl 2 melt leads to a drop in electronic conductivity. The introduction of sodium chloride produces a greater drop in the electronic component than does lithium chloride. Nevertheless, even with sufficiently large dilutions the electron transfer remains considerable.This experimental fact shows great promise for the use of CuCl-CuCl 2 melt as a cathodic material in high-temperature batteries employing Li/CuCl-CuCl 2 and Na/CuCl-CuCl 2 electrochemical systems.We used the Nernst-Einstein equation to calculate the effective values of electron diffusion coefficients. The latter greatly exceed the values of Li + and Na + diffusion coefficients, usual for chloride melts, with dilution they drop in value and gradually become equal to zero.We examined various mechanisms of transfer of electrons from cation Cu + to Cu 2 + in the investigated systems. It was assumed that the contribution to the electron transfer is made not by the direct interaction between cations Cu + and Cu 2 + but by their interaction through the medium of a Cl - anion.