Glassy electrolytes

The polymer electrolytes discussed so far suffer from a number of disadvantages. Firstly, they exhibit low conductivities in comparison with liquid or solid (crystalline or glassy) electrolytes at or below room temperature. The best all-amorphous systems have conductivities less than 10"4 S cm-1 at room temperature. These ambient... 

All ion-exchanger membranes with fixed ion-exchanger sites are porous to a certain degree (in contrast to liquid membranes and to membranes of ion-selective electrodes based on solid or glassy electrolytes, such as a single crystal of lanthanum fluoride). 

This type of membrane consists of a water-insoluble solid or glassy electrolyte. One ionic sort in this electrolyte is bound in the membrane structure, while the other, usually but not always the determinand ion, is mobile in the membrane (see Section 2.6). The theory of these ion-selective electrodes will be explained using the glass electrode as an example this is the oldest and best known sensor in the whole field of ion-selective electrodes. 

Another approach has been developed by Bruno and Della Monica [24-26], This work takes the Vogel-Tamman-Fulcher (VTF) equation, which has been used to rationalize transport properties in molten salts and glassy electrolytes, and modifies it for nonaqueous solutions. The work follows the development of Angell and co-workers [27,28], who carried out a similar development for aqueous solutions. The expression used is... 

The data presented in Table 1 permit several conclusion to be drawn on the potential use of these materials as electrolytes in electrochemical devices with practical values for the area-specific resistance. Only the j0"-alumina and NASICON electrolytes possess sufficient conductivities for use as membranes with thicknesses of 1 mm or greater. The sodium ion conductivities of polycrystalline NASICON and /l"-alumina are comparable. The glassy electrolytes must be used in the form of thin films ( < 50 pm and possibly under 10-15 pm) or as capillary tubes with very thin walls (10-50 pm). 

The understanding of transport in glassy electrolytes appears to be even less developed than that in polymers. Glassy electrolytes are inhomogeneous on a 1-10 nm scale and the conductivity has been discussed in terms of intra and intercluster jumps . For iono-covalent hard glasses, a... 

Knodler D, Dieterich W, Petersen J (1992) Coulombic traps and ion conduction in glassy electrolytes. Solid State Ionics 53 1135-1140... 

Chandra A, Bhatt A, Chandra A (2013) Ion conduction in superionic glassy electrolytes an overview. J Mater Sci Technol 29 193-208... 

Although higher conductivities are preferable, 100-fold or 1000-fold increases are not essential, as a thin-film electrochemical cell configuration can largely compensate for these lower values. Less favorable is the tendency for ion association and low cationic relative mobility (a property shared with aprotic liquids, as opposed to ceramic or glassy electrolytes) in polyether-based materials. These fundamental properties can affect cell performance and must influence the design of new polymeric electrolytes to make them competitive as battery materials. 

The polymer electrolytes discussed so far suffer from a number of disadvantages. Firstly, they exhibit low conductivities in comparison with liquid or solid (crystalline or glassy) electrolytes at or below room temperature. The best all-amorphous systems have conductivities less than 10 S cm at room temperature. These ambient temperature conductivities may be insufficient in some cases for the power required by a lithium battery. Secondly, the interfacial impedances present at both the lithium anode (passivation) and composite cathode (passivation, contact) are in addition to the ohmic losses in the electrolyte. Thirdly, the lowness of cation transference number, although similar to the values in liquid systems, is a major issue since the total conductivity is lower and could limit the use of solvent-free polymer electrolytes except in the form of extremely thin films or above room temperature. 

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