Properties and Applications of Solid Solution Electrodes

Abstract

Selected materials can function as a host lattice for the incorporation of elements such as hydrogen, oxygen, copper, lithium, sodium which may be employed as the electroactive species in a variety of electrochemical devices. Providing the solubility of the relevant species is relatively large and that the rate of dissolution is fast then these materials can be used as SOLID SOLUTION ELECTRODES (S.S.E.) in appropriate electrochemical cells. The criteria for a non-stoichiometric S.S.E., AxMXy incorporating electroactive species A have been discussed by Steele (1) and may be summarised as follows: 1. Good electronic conductor 2. Large range of homogeneity e.g. 0<x<1 3. ΔḠa (ΔHa) relatively constant over wide range of composition 4. Rapid chemical diffusion (Da) of electroactive species within non stoichiometric electrode in both directions. As a shallow ΔḠ - composition curve is specified (3rd criterion), then the magnitude of the relevant chemical and self diffusion coefficients will be similar (Da ~ Da *~ 10−6 cm2/s). The S.S.E. should therefore be a good ionic conductor. 5. Rapid transfer of electroactive species A across the S.S.E. / electrolyte interface. 6. Ability to form stable interfaces with relevant electrolyte phase. 7. For mass production constituents should be cheap, abundant, and easily fabricated into desired component.