Composite solid electrolyte systems

In most solid electrolyte systems, it is not possible to vary the composition sufficiently so as to have the complete spectrum of mobile ion concentrations, from n,. = 0 to n,. = 1. Instead, the properties are usually limited to one or other of the wings in the type of behaviour... 

Ionically conducting polymers and their relevance to lithium batteries were mentioned in a previous section. However, there are several developments which contain both ionically conducting materials and other supporting agents which improve both the bulk conductivity of these materials and the properties of the anode (Li)/electrolyte interface in terms of resistivity, passivity, reversibility, and corrosion protection. A typical example is a composite electrolyte system comprised of polyethylene oxide, lithium salt, and A1203 particles dispersed in the polymeric matrices, as demonstrated by Peled et al. [182], By adding alumina particles, a new conduction mechanism is available, which involved surface conductivity of ions on and among the particles. This enhances considerably the overall conductivity of the composite electrolyte system. There are also a number of other reports that demonstrate the potential of these solid electrolyte systems [183],... 

Uvarov N, lusupov V, Sharama V, Shukla K (1992) Effect of morphology and particle size on the ionic conductivities of composite solid electrolytes. Solid State Ionics 51 41-52 Uvarov NF, Ponomareva VG, Lavrova GV (2010) Composite solid electrolytes. Russ J Electrochem 46(7) 722-733 Vaidehi N, Akila R, Shukla A, Jacob KT (1986) Enhanced ionic conduction in dispersed sohd electrolyte systems CaFj-AljO, and CaF -CeO. Mater Res Bull 21 909-916... 

The possibility of plasma copolymerization and the production of composite materials allows to design at the molecular level thin films of very low electronic conductivity, but with very high ionic conductivity. Such films can be obtained in the polymer-like form (polymer electrolytes) and as ionic glasses (solid oxide electrolytes). These new solid electrolyte systems enable us to replace the conventional solid electrolytes by the much thinner elements, which in addition have all the other advantages of plasma fabricated materials, for example, selective permeability. Thin films of solid electrolytes produced by cold plasma deposition techniques have been of particular interest recently. 

The galvanic cell studied (shown in Fig. 5.24) utilizes a highly porous solid electrolyte that is a eutectic composition of LiCl and KCl. This eutectic has a melt temperature of 352 °C and has been carefully studied in prior electrochemical studies. Such solid electrolytes are typical of thermal battery technology in which galvanic cells are inert until the electrolyte is melted. In the present case, shock compression activates the electrolyte by enhanced solid state reactivity and melting. The temperature resulting from the shock compression is controlled by experiments at various electrolyte densities, which were varied from 65% to 12.5% of solid density. The lower densities were achieved by use of microballoons which add little mass to the system but greatly decrease the density. 

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. 

The lithium polymer battery (LPB), shown schematically in Fig. 7.21, is an all-solid-state system which in its most common form combines a lithium ion conducting polymer separator with two lithium-reversible electrodes. The key component of these LPBs is the polymer electrolyte and extensive work has been devoted to its development. A polymer electrolyte should have (1) a high ionic conductivity (2) a lithium ion transport number approaching unity (to avoid concentration polarization) (3) negligible electronic conductivity (4) high chemical and electrochemical stability with respect to the electrode materials (5) good mechanical stability (6) low cost and (7) a benign chemical composition. 

Instead of the system silica/silicate also other systems such as titania/titanate, zirconia/zirconate can be used as a reference system [xiv]. The response time of freshly fabricated thick-film sensors based on thin-film /3-alumina is very short (about 15 ms at 650 °C). After several weeks of operating this time increases 10 times (150 ms) [xv]. Solid electrolyte C02 sensors using Ni/carbonate composite as measuring electrode are suited for measuring of C02 in equilibrated water gases [xiv]. Using semiconducting oxides and carbonates like ITO (indium tin oxide) Nasicon-based C02 sensors are able to measure at room temperature [xvi]. 

Other than compounds, the activities of CaO in solid solutions have also been measured using CaFj solid electrolyte. The CaO-CdO system is one such example. Here also CaO and CdO are both having NaCl-type FCC lattice structure and are fully miscible in the entire composition range. Through the measurement of EMF of the following cell, the activities of CaO in the CaO-CdO solid solutions were determined Prasad et al, 1975)... 

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