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Solid: Sodium Ions

Introduction: The ceramic oxide known as ‘beta alumina’ exhibits remarkably high conductivity of sodium ions and, as a consequence, has been adopted as a key component in batteries that employ liquid sodium as the active material at the negative electrode. Most rechargeable (or ‘secondary’) batteries comprise solid electrodes and a liquid electrolyte. A separator is placed in the electrolyte between the plates to prevent a short circuit. | Solid Sodium Ions PT Moseley International Lead Zinc Research Organization Inc. Research Triangle Park NC USA 2009 Elsevier B.V. All rights reserved. Introduction The ceramic oxide known as beta alumina exhibits remarkably high conductivity of sodium ions and as a consequence has been adopted as a key component in batteries that employ liquid sodium as the active material at the negative electrode. Most rechargeable or secondary batteries comprise solid electrodes and a liquid electrolyte. A separator is placed in the electrolyte between the plates to prevent a short circuit. High-temperature sodium batteries on the contrary have electrode active materials that are liquid at the operating temperature 250-350 C with the ceramic beta alumina placed between them performing the twin functions of electrolyte and separator. The requirements for the material to act as electrolyte and separator in the cell are extremely demanding including total retention of integrity in aggressive environments at high temperatures. Also in view of the market demands for a device with a reliable capability of at least 1000 deep charge discharge cycles neither the mechanical properties nor the electrical specification for a high ionic and zero electronic conductivity can be allowed significant shortfall or degradation over long periods. Applications of Beta Alumina The convenient properties of beta alumina were first exploited in the concept of sodium sulfur cells. The ceramic is formed into open-ended tubes with one liquid electrode on the inside and the other round the outside in a concentric outer container. Liquid sodium forms the negative electrode and liquid sulfur in intimate contact with a conducting current collector material forms the positive plate. Energy is stored and released through reactions of sodium ions after passage through the electrolyte with sulfur to form a sequence of sodium sulfides. The electrode volumes are sealed from the atmosphere and the cell is operated at .