Solid state cells

There are two classes of materials which may be used as electrolytes in all-solid-state cells polymer electrolytes, materials in which metal salts are dissolved in high molar mass coordinating macromolecules or are incorporated in a polymer gel, and ceramic crystalline or vitreous phases which have an electrical conductance wholly due to ionic motion within a lattice structure. The former were described in Chapter 7 in this 

The second necessary condition for crystalline or vitreous solid to have high ionic conductivity is that the mobile ions have a high diffusion coefficient, i.e. it is indeed a fast ion conductor . Much attention has been given to developing models of ionic motion. The simple hopping models applied successfully in the case of defect transport are not appropriate because of the high density of mobile ions in solid electrolytes, and 

Since the discovery of the MAg4I5 compounds, very many more solid electrolytes have been reported. Sodium, lithium, copper, proton, oxide and fluoride solid electrolytes are now well known. An important example is sodium /3-alumina which was discussed in Chapter 8. The conductance 

However, high electrolyte conductivity on its own does not necessarily guarantee low polarization in a solid state cell. Electrode/electrolyte inter-facial resistance must also be taken into account, and in contrast to the more familiar situation with conventional aqueous systems where the solid electrodes are uniformly wetted by the liquid electrolyte, the all-solid configuration of the cell may create non-uniform contact at the interfaces. Differential expansion and contraction of electrodes and electrolyte may lead to poor contact (and consequent high internal resistance due to low effective electrode/electrolyte interfacial area) or even to a complete open circuit during cell operation. The situation is even more serious with secondary cells, as illustrated schematically in Fig. 9.4, where the effects 

The only commercial ambient solid state batteries so far produced have been based on either silver or lithium anodes and these will now be described. 

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What is the practical usefulness of the soe scale of solid state electrochemistry As in aqueous electrochemistry, it is limited but not trivial. When a potential Uwr of, e.g. -300 mV is measured in an YSZ solid state cell at 673 K vs a reference electrode at p02=l atm, the implication is that the work function of the reference electrode is 5.14 eV and that of the working electrode 4.84 eV regardless of the material of the two electrodes. 

III, F. More phase diagrams of complex fluorides have been explored using Knudsen cell mass spectrometry (13, 15), and electron impact studies have yielded enthalpies and bond energies (1,3). The heat of formation of MoFmi) has been confirmed (12). Solid state cells have been used with lanthanide trifluorides (24) and NaNiF3 (21). 

It is now time to look at the Nyquist impedance plot of a real cell. Figure 8.12(a) shows such an impedance plot for the all-solid-state cell, IT0/W03/PE0-H3P04/1T0(H), at 8°C. The two ITO layers are needed as transparent electronic conductors (cf. Section 8.1.2). 

Figure 8.12 (a) Nyquist plot obtained for the all-solid-state cell, ITOAVO3/PEO-H3PO4/ ITO(H) at 8°C, with the electrolyte being unplasticized. The WO3 layer was 0.3 pm in thickness (as gauged during vacuum evaporation with a thin-film monitor), while the electrolyte thickness was 0.24 mm (achieved by using 0.3 mm spacers of inert plastic placed between the two ITO electrodes), (b) Schematic representation of the equivalent circuit for this cell. 

At this time the only commercially available all-solid-state cell is the lithium battery containing Lil as the electrolyte. Many types of solid lithium ion conductors including inorganic crystalline and glassy materials as well as polymer electrolytes have been proposed as separators in lithium batteries. These are described in the previous chapters. A suitable solid electrolyte for lithium batteries should have the properties... 

More recently, TiCVCuSCN heterostructures have been used in multilayer solid-state cells characterized by a broader spectral response. It has been shown that the electron injection from a photoexcited dye can occur through ultrathin layers... 

Fig. 2.9 Current pathways in a solid state cell the electrode consists of granular silver metal and solid electrolyte...

Almost all modern practical aqueous primaries are referred to as dry cells . This designation should not be confused with the rather specialized solid state cells which make use of the recently discovered true solid electrolytes. Rather, the term implies that the aqueous electrolyte phase has been immobilized by the use of gelling agents or by incorporation into microporous separators. Such procedures permit the cells to operate in any orientation and reduce the effects of leakage should the container become punctured. 

Fig. 9.5 Ag-Rbtj solid state cell. (By permission of John Wiley B.B. Owens, Advances in Electrochemistry and Electrochemical Engineering, vol, 8, eds P, Delahay and C, W, Tobias. 1971, p. 1.)...

Fig. 9.10 Construction of lithium-iodine solid state cell for PCB mounting. (By courtesy of Catalyst Research Corporation.)...

Another type of lithium solid state cell which reached the quasi-commercial stage was developed in the mid-1980s by Eveready. This cell used a vitreous inorganic electrolyte formed by a mixture of Lil and Li8P4Oo,25S 13.75. This solid electrolyte had a reasonably high conductivity which allowed cell operation at ambient temperatures. A disadvantage was its high reactivity which imposed the use of severe fabrication controls (e.g. assembly in a strictly moisture-free environment). 

Fig. 9.16 Discharge characteristics at 218C of the Li-TiS2 solid state cell, type XR 2016. (By permission of Eveready.)...

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