Copper-ion solid-state battery systems involving sulphonium iodide electrolytes
THE past 10 years has seen a considerable interest in solid-state battery systems involving electrolytes based on silver iodide1–3. Studies of electrolytes involving organic sulphonium iodides in conjunction with silver iodide have been reported3,5–9, but recently the possibility of using cuprous ions to replace silver ions as the mobile species has attracted attention, because of the potential advantage of lower cost and higher voltage. We report here the results of our investigations of sulphonium iodide–cuprous iodide electrolytes.
Solid state batteries containing silver sulphonium iodide electrolyte
THE high ionic conductivity α phase of AgI can be stabilised at room temperature by the addition of various inorganic or organic salts (such as Ag4RbI5, ref. 1) to the AgI. These systems have attracted considerable interest as electrolytes in solid state batteries2,3.
Solid Ionics—Solid Electrolyte Cells
The characteristics of the solid electrolyte cells Ag /RbAg4IJTe and Ag/RbAg4Is/Se have been studied. The open-circui t voltages of these solid electrolyte cells were 0.217V and 0.265V, respectively, at 20~ These cells could discharge in the temperature range of --75 ~ to 150~ Only a small polarization was observed at relat ively high current density discharge. Diffusion coefficients of Ag in these systems were also evaluated from the t imedependent behavior of the cell voltage as a function of current density. Although the various types of solid electrolyte cells have been investigated by many authors (1-3), most of them were able to discharge only in the microampere range at room temperature, the reason being the poor conductivi ty of the electrolyte used. Recently, as higher ionic conductivi ty solid electrolytes have been found (4-8), a high performance solid electrolyte cell operating in a mil l iampere range at ambient temperature has been developed. Previous investigations on solid electrolyte have dealt almost exclusively with the simple compounds like silver halides, the highest conductivi ty of which was between 10-6 and 10 -5 ohm -1 cm -1 at room temperature. In recent years, in o r d e r to find high ionic conductivi ty solids, the solid state reaction products of b inary and te rnary systems have been studied by Takahashi, Bradley and Owens, and Ag3SI (4), Ag2Hg0.25So.sI1.5 (5), Ag4HgSe212 (6), and RbAg415 (7, 8) have been found to have high ionic conductivities at room tempera ture (Table I) . Accordingly by using these high ionic conductivity solids as electrolytes, it is possible to make an excellent solid electrolyte cell by combining it with a suitable electrode. As silver ions are charge carriers in these compounds, silver is always used for the anode. The cathode mater ia l of solid electrolyte cells should have the properties of: (i) showing as positive a potential as possible, (ii) ease of forming thin film, (iii) a low discharge polarization, and (iv) discharge product funct ioning as a silver ion conductor. Requirements i and ii are necessary for at taining compactness and high voltage of the cell, while requirements iii and iv are for obtaining a high current density. Takahashi et al. (9) reported a solid electrolyte cell, Ag/Ag~SI/I2, and Argue et al. (10) the cell Ag/RbAg4IJRbI3, with cell voltages of 0.67 and 0.66V, respectively, and these cells can discharge at relat ively high current density. The ionic conductivi ty of solids such as Ag~SI and RbAg415 is relat ively unstable in iodine atmosphere, especially at high temperature, and iodine vapor is so highly corrosive for metals, that the celI must be gastight. In this paper a solid electrolyte cell is described in which the vapor pressure of the cathode mater ial is very low over a wide temperature range and the high voltage * E l e c t r o c h e m i c a l S o c i e t y A c t i v e M e m b e r . is main ta ined dur ing discharge even at a high current density. Results of our search for substances which satisfy the above stated requirements have indicated te l lur ium and selenium to be excellent. Te l lur ium is a solid having a very low vapor pressure and high electrical coDductivity (2.6 ohm -1 cm -1 at 20~ at room tempera ture and a mel t ing point of 450~ Fur thermore, te l lur ium is capable of forming a th in film easily by vacuum evaporation. The mel t ing point of selenium is 217~ and the vapor pressure at room tempera ture is low enough. The electrical conductivi ty of selenium, 10 -5 ohm -1 cm -1 at room temperature, is substant ial ly less than that of tel lurium. Selenium can also form a thin film readily by vacuum evaporation. In this paper, the performances of the cell Ag /RbAg4 l JTe or Se are described.