Design Aspects of Solid Electrolytes

Generally, the interpretation and reliability of published experimental data for solid electrolytes should be regarded with care. The most important experimental methods are presented in Sec. 9.6. 

In spite of the extraordinarily high ionic conductivity of silver- and copper-ion conductors, these materials suffer from their low capacity and energy density. In addition, only a few positive electrode materials have been found until now. 

Some fluorine-ion conductors exhibit high ionic conductivities, even at room temperature [4], which are not equaled by other halide-ion conductors. However, there is a lack of known electrode materials. Further research on this topic is very worthwhile. 

Apart from applications in sensons [21, 22], divalent-ion conductors, e.g., for Mg ions, are of great interest for thin film batteries which may be incorporated into microelectronics as memory backups and into other applications. For these batteries high volumetric specific energy densities rather than high current densities are required, and thin films offer in addition a major decrease in the total ionic resistance. 

Most of the recent research focuses on proton, lithium, sodium and potassium batteries. This is not only for the reasons discussed above. The availability of a large variety of electrodes also plays an important role. Furthermore, high voltages rather than high currents are favorable from a practical point of view. 

Four major aspects should be taken into consideration for the design of suitable solid electrolytes  

However, in the case of the perovskite, even the application of sintering temperatures as high as 1200°C did not result in a higher overall ionic conductivity. Since the total ionic conductivity is 2 orders of magnitude lower than the bulk conductivity in polycrystaUine Lio.34 Lao.si Ti02.94, an improvement by way of the preparation route is necessary rather than changes in the lattice by the addition of dopants. 

The third aspect the stability range of solid electrolytes, is of special concern for alkahne-ion conductors since only a few compounds show thermodynamic stability 

Traditionally, the chemical stabihty of the electrode/electrolyte interface and its electronic properties have not been given as much consideration as structural aspects of solid electrolytes, in spite of the fact that the proper operation of a battery often depends more on the interface than on the solid electrolyte. Because of the high ionic conductivity in the electrolyte and the high electronic conductivity in the electrode, the voltage falls completely within a very narrow region at the electrolyte/electrode interface. 

Some further important aspects for the design of sohd electrolytes and solid electrodes for battery-type applications are the following  

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Unique Performance Parameters and Design Aspects of Solid Electrolyte Cells... 

Outstanding performance capabilities and design aspects of solid electrolyte cells are briefly summarized as follows ... 

The third aspect, the stability range of solid electrolytes, is of special concern for alkaline-ion conductors since only a few compounds show thermodynamic stability with, e.g., elemental lithium. Designing solid electrolytes by considering thermodynamic stability did lead to very interesting compounds and the discovery of promising new solid electrolytes such as the lithium nitride halides [27]. However, since solid-state reactions may proceed very slowly at low temperature, metasta-... 

In the past decade, much development has taken place in regard to measuring the forces involved in these colloidal systems. In one method, the procedure used is to measure the force present between two solid surfaces at very low distances (less than micrometer). The system can operate under water, and thus the effect of addictives has been investigated. These data have provided verification of many aspects of the DLVO theory. Recently, the atomic force microscope (AFM) has been used to measure these colloidal forces directly (Birdi, 2002). Two particles are brought closer, and the force (nanoNewton) is measured. In fact, commercially available apparatus are designed to perform such analyses. The measurements can be carried out in fluids and under various experimental conditions (such as added electrolytes, pH, etc.). 

In the late 1970s, polymer electrolyte materials were proposed for use in solid-state battery designs." A considerable development effort has resulted in a number of review arti-cles" " describing the status of such batteries in some detail. The unique aspect of these batteries is that the electrolyte is a soM flexible film comprised of a polymer matrix and an ionic salt complexed into the matrix. Thin-film solid-polymer electrolyte batteries offer tbe possibility of an intrinsically safe battery design in combination with good high-rate capability. 

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