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.
Search for new silver-ion solid electrolytes for use in batteries
THE α-phase of AgI, which is stable above 146 °C, has a silver-ion conductivity of 1 Ω−1 cm−1 at 150 °C (ref. 1), which would make it a suitable solid electrolyte for high temperature batteries. The room-temperature conductivity of the stable phase of AgI is disappointingly low (10−6−6 Ω−1 cm−1) and although samples with conductivities approaching 3 × 10−4 Ω−1 cm−1 can be prepared2, such values are insufficient to make it of use as an electrolyte in solid state batteries at room temperature. There is, however, considerable interest in producing solid electrolytes, based on AgI combined with organic cation iodides to give high silver-ion conductivity at room temperature4–9. We report here on the conductivities of representatives of three hitherto unexamined classes of compounds, AgI–selenonium iodide, AgI–telluronium iodide and AgI–bis-sulphonium diiodide.
Recent progress in the development of solid electrolyte batteries
Solid electrolyte batteries may be loosely defined as power sources within which the transfer of the ionic species between the cathode and anode plates occurs by migration through a solid as opposed to a liquid phase. Within this definition one may include those systems which have, for example, a gaseous depolarizer and which can not therefore be classified in the strictest sense as "all-solid" batteries. Again, it should be pointed out that the use of the term "solid" does not imply that such systems may be thought of as "dry". Indeed, there is a considerable volume of evidence, which will be mentioned later, to indicate that no solid electrolyte system which has been developed to date can operate without the presence of a trace liquid phase. In spite of these limitations, however, solid electrolyte systems have a number of quite unique advantages which can not be as readily fulfilled by present day state of the art liquid electrolyte units. For example, such systems can be assembled into extremely rugged configurations and may thus be used in applications which require a battery that will withstand acceleration forces of the order of several thousand times that due to gravity coupled with spin rates of several hundred revolutions per second. Further, with liquid electrolyte batteries one is limited to that range of temperatures between which the electrolyte freezes and boils and also with loss of the electrolyte on long term standby processes of evaporation and leakage. To a large extent such problems may be avoided by the use of solid electrolytes though for those systems which utilize a gaseous depolarizer one also encounters problems associated with the sealing of the unit. Perhaps the most the use of a solid miniature batteries important advantage associated with electrolyte is the ease with which may be produced. As a general statement it is true to say that the power requirements of electronic devices are continually being reduced by the development of more sophisticated micro-electronic circuit components and hence if the advances made in these areas are to be utilized to the fullest extent there must be a corresponding reduction in the size of the power source. With the present day liquid electrolyte systems, however, the problem of containment of the liquid phase constitutes an increasingly greater problem