Conduction mechanism, molten carbonate electrolytes

Structural studies in fused salts by means of careful and thorough high-temperature measurements of electrical conductivity, density, viscosity, and laser- Raman spectroscopy have been reviewed. Four problem areas are discussed (1) melting mechanisms of ionic compounds with large polyatomic cations, (2) salts as ultra-concentrated electrolyte solutions, (3) structural aspects and Raman spectroscopy, and (4) electrolysis of molten carbonates. The results in these areas are summarized and significant contributions to new experimental techniques for molten-salt studies are discussed.275 The physical properties and structure of molten salts have also been reviewed in terms of operational (hole, free volume, partly disordered crystal) and a priori (intermolecular potential) models.276 Electrochemistry... 

O.K. Davtyan of the Soviet Union did many experiments to increase the conductivity and mechanical strength of the electrolyte in the 1940s. Many of the designs did not yield the desired results, but Davtyan s and Baur s work contributed to the necessary preliminary research for today s current molten carbonate and solid oxide fuel cell devices [11,13, 35]. 

Lithium batteries use nonaqueous solvents for the electrolyte because of the reactivity of lithium in aqueous solutions. Organic solvents such as acetonitrile, propylene carbonate, and dimethoxyethane and inorganic solvents such as thionyl chloride are typically employed. A compatible solute is added to provide the necessary electrolyte conductivity. (Solid-state and molten-salt electrolytes are also used in some other primary and reserve lithium cells see Chaps. 15, 20, and 21.) Many different materials were considered for the active cathode material sulfur dioxide, manganese dioxide, iron disulfide, and carbon monofluoride are now in common use. The term lithium battery, therefore, applies to many different types of chemistries, each using lithium as the anode but differing in cathode material, electrolyte, and chemistry as well as in design and other physical and mechanical features. 

Although in refractory practice there are hundreds of heat insulation materials, the list of heat insulation materials for the lining of reduction cells is rather limited. For one thing, economic considerations add some limitations, but for another, the heat insulation materials in reduction cells should withstand mechanical compression loads without deformation at temperatures up to 900 °C for a long time, and numerous inexpensive fiber heat insulation materials don t correspond to this requirement. In the Hall-Heroult reduction cell, the heat insulation materials should withstand the pressure of the layer of the electrolyte, the layer of molten aluminium, cathode carbon blocks (taking into account collector bars), and the refractory layer. Currently, only four or five heat insulation materials are used in the lining of reduction cells diatomaceous (moler) and perlite bricks, vermiculite and calcium silicate blocks (slabs), and sometimes lightweight fireclay bricks (but their thermal conductivity is relatively big, while the cost is not small) and fiber fireclay bricks. 

---