Electrolyte materials

The electrolytes are required to be solid in applications where the electrochemical device must operate at temperatures too high for liquid electrolytes or thin films of the electrolytes. Solid electrolytes are materials exhibiting high ionic conductivity with negligible electronic conductivity and are thermodynamically stable under conditions of the application. Many of the mixed oxide systems satisfy this requirement. Mixed oxides with high conductivities of both ions and electrons are named mixed conductors and are used together with electrolytes in many applications. 

The mechanical properties of such electrolytes are mainly controlled by the segregation of vitreous phases at the grain boundaries. The optimization of the properties of ion-conducting materials is relatively limited, and both the construction and performances of the electrochemical celk are often determined by the properties of materials available. Therefore, the development of materials with satisfactory properties for high-temperature electrochemical applications is an important scientific task. 

Perovskites and Related Mixed Oxides Concepts and Applications, First Edition. 

Edited by Pascal Granger, Vasile I. Parvulescu, Serge Kaliaguine, and Wilfrid Prellier. 

Nanostructured materials have attracted great interest for many different applications, due to their unusual or enhanced properties compared with bulk materials [9-12]. An example of enhanced property of nanomaterials producing ad-value is the ionic conductivity. Therefore, the investigation of the nanostructured solid conductors, also known as nanoionics, has recently become one of the hottest fields of research. These nanomaterials can be used for advanced energy conversion and storage applications, such as SOFCs. Various synthetic routes, such as thermal evaporation [13], wet chemical processes including coprecipitation [14], the modified sol-gel method [15], the hydrothermal process [11,16], mixing freeze-dried precursors [17], or the combustion [18], have already been developed to produce solid electrolytes composed from nanosized crystallites. 

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All flashlight batteries, button batteries, compact rechargeable batteries and vehicle storage batteries operate under the same basic principles. An electrochemical cell is constructed of two chemicals with different electron-attracting capabilities. Called an electrochemical couple, these two chemicals, itntncrscd in an electrolyte (material that carries the flow of energy between electrodes), are connected to each other through an external circuit. 

Improve electrolyte material, using better conductors that are still chemically compatible with the electrodes. 

Identify electrode and electrolyte material that is inexpensive and readily available in order to achieve a low-cost battery. 

Unlike the PEM, the ionic conduction occurs for the oxygen ion instead of the hydrogen ion. SOFCs are made of ceramic materials like zirconium (Z = 40) stabilized by yttrium (Z = 39). High-temperature oxygen conductivity is achieved by creating oxygen vacancies in the lattice structure of the electrolyte material. The halfcell reactions in this case are... 

Hayashi et al. [50] investigated the electrolyte materials and their compositions with various carbonates and ethers as... 

Another influence that electrolyte materials have on the cycle life of a practical lithium cell results from the evolution of gas as a result of solvent reduction by lithium. For example, EC and PC give rise to [53] evolution of ethylene and propylene gas, respectively. In a practical sealed-structure cell, the existence of gas causes irregular lithium deposition. This is because the gas acts as an electronic insulator and lithium is not deposited on an anode surface where gas has been absorbed. As a result, the lithium cycling efficiency is reduced and shunting occurs. 

It is generally considered that the lithium surface film is produced by a reaction between the lithium and the electrolyte materials. However, by XPS we have detected vanadium on a lithium anode surface cy-... 

In solid-state systems it is often advantageous to have some of the electrolyte material mixed in with the reactant. There are two general advantages that result from doing this. One is that the contact area between the electrolyte phase and the electrode phase (the electrochemical interface) is greatly increased. The other is that the presence of the electrolyte material changes the thermal expansion characteristics of the electrode structure so as to be closer to that of the pure electrolyte. By doing so, the stresses that arise as the result of a difference in the expansion coefficients of the two adjacent phases that can use mechanical separation of the interface are reduced. 

Reactivity of e ol with Electrolyte Components - a Tool for the Selection of Electrolyte Materials... 

In the Na/S system the sulfur can react with sodium yielding various reaction products, i.e. sodium polysulfides with a composition ranging from Na2S to Na2S5. Because of the violent chemical reaction between sodium and sulfur, the two reactants have to be separated by a solid electrolyte which must be a sodium-ion conductor. / " -Alumina is used at present as the electrolyte material because of its high sodium-ion conductivity. 

Consequently the absolute potential is a material property which can be used to characterize solid electrolyte materials, several of which, as discussed in Chapter 11, are used increasingly in recent years as high surface area catalyst supports. This in turn implies that the Fermi level of dispersed metal catalysts supported on such carriers will be pinned to the Fermi level (or absolute potential) of the carrier (support). As discussed in Chapter 11 this is intimately related to the effect of metal-support interactions, which is of central importance in heterogeneous catalysis. 

If excess electrolytic materials are present, competition for charge will occur. The efficiency with which the analyte will be ionized depends upon the concentration of each of the species present and also the relative efficiency of the conversion of each to the gas phase. 

Alkaline solutions are generally known to lead to better catal5Tic activities than acidic solutions for many relevant electrode reactions. However, owing to the paucity in the development of suitable electrolyte materials, such as alkaline membranes, there has been much less fundamental work in the area of fuel cell catalysis in alkaline media. Nevertheless, there are a few hopeful developments in new alkaline polymer membranes [Varcoe and Slade, 2005] that are currently stirring up interest in smdying fuel cell catalytic reactions in alkalme solution. 

Boroxine ring-containing polymers have found extensive use in the development of polymeric electrolyte materials used in ion-selective transport membranes. Matsumi and Ohno cover this area in Chapter 6 of this book. 

SEM images indicate that both graphite samples have very similar morphologies. Negative electrode laminates with active materials of SL-20 and SLC-1015 were then prepared using similar compositions. These laminates were then used to prepare negative electrodes that were inserted into Li-ion cells having similar cathodes and electrolyte materials. 

The potential benefits of plasma spraying as an SOFC processing route have generated considerable interest in the process. In the manufacture of tubular SOFCs, APS is already widely used for the deposition of the interconnect layers on tubular cells, and has also been used for the deposition of individual electrode and electrolyte materials, with increasing interest in utilizing APS rather than EVD for electrolyte deposition due to the high cost of the EVD process [48, 51,104],... 

Zhitomirsky I and Petrie A. Electrophoretic deposition of electrolyte materials for solid oxide fuel cells. J. Mater. Sci. 2004 39 825-831. 

La O GJ, Hertz J, Tuller H, and Shao-Hom Y. Microstructural features of RF-sputtered SOFC anode and electrolyte materials. J. Electroceram. 2004 13 691-695. 

Intermediate Temperature Solid Oxide Fuel Cell (ITSOFC) The electrolyte and electrode materials in this fuel cell are basically the same as used in the TSOFC. The ITSOFC operates at a lower temperature, however, typically between 600 to 800°C. For this reason, thin film technology is being developed to promote ionic conduction alternative electrolyte materials are also being developed. 

Improvements in solid polymer electrolyte materials have extended the operating temperatures of direct methanol PEFCs from 60 C to almost 100 C. Electrocatalyst developments have focused on materials that have higher intrinsic activity. Researchers at the University of Newcastle upon Tyne have reported over 200 mA/cm at 0.3 V at 80 C with platinum/ruthenium electrodes having platinum loading of 3.0 mg/cm. The Jet Propulsion Laboratory in the U.S. has reported over 100 mA/cm at 0.4 V at 60 C with platinum loading of 0.5 mg/cm. Recent work at Johnson Matthey has clearly shown that platinum/ruthenium materials possess substantially higher intrinsic activity than platinum alone (45). 

Watakabe, A. 2005. Polymer electrolyte fuel cell, electrolyte material therefore and method for its production. US Patent 2005037265. 

These simple considerations lead to the following general criteria for the quality of a solid-electrolyte material to be used in an electrochemical cell. 

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