Until recently, electrochemistry has been mainly involved with liquid electrolytes, traditionally molten and dissolved electrolytes. Because their domain of electroactivity is often too narrow and their selectivity is poor with respect to the nature of the charge carrier, these electrolytes have proved unsuitable for energy storage in high density energy storage batteries. Consequently, in recent years a great deal of research has been devoted to another type of electrolyte: crystallized solid state electrolytes. Roughly, there are two types of solid electrolytes. First there are electrolytes conducting through point defects. These include alkali and alkaline earth halides and some oxides. They have a compact crystalline structure, and ion displacement is only possible because of point defects such as vacancies or interstitial ions. These conductors present an intrinsic conduction, associated with the con centration of defects of thermal origin, Frenkel or Schottky disorder, and an extrinsic conduction associated with the concentration of point defects in the ionic or cationic sublattice created by impurities. Intrinsic and extrinsic conduction are both characterized by an activation energy. The intrinsic conduction activation energy is always high since it is the sum of two terms-one representing the energy needed to form a point defect, and the second the migration energy of this defect. In the extrinsic domain, at lower temperature, the activation energy is lower since it reflects only the migration energy. The value I eV often constitutes a boundary between the two types of conduction. Secondly, there are solid state electrolytes that conduct through dis order of the sub lattice of one of the ions. They include electrolytes such