Solid electrolytes conduction

The electrical conductivity of the involved solid electrolytes must be exclusively ionic, the charge carrier being an ion associated with the oxidant (O2) or the fuel (H2> hydrocarbons, etc.). Then the choice is reduced to solid electrolytes conducting by O2 or H+. The required properties for these materials, fixed by both electrochemical constraints and the high operating temperature, are the following ... 

The response to the applied perturbation, which is generally sinusoidal, can differ in phase and amplitude from the applied signal. Measurement of the phase difference and the amplitude (i.e. the impedance) permits analysis of the electrode process in relation to contributions from diffusion, kinetics, double layer, coupled homogeneous reactions, etc. There are important applications in studies of corrosion, membranes, ionic solids, solid electrolytes, conducting polymers, and liquid/liquid interfaces. 

The development of novel oxygen solid electrolytes conducting at temperatures below 800 °C is of major importance in the large-scale development of applications. 

The dry glass core in a pH electrode exhibits solid electrolytic conductance, not semiconductive. The electrode is proton sensitive, but the small conductivity in the glass core stems from Li" ", Na" ", and K, which have mobilities 10 —10" larger than the protons. However, water is absorbed in the leached surface layers of the glass, and there the proton mobility is high and contributes to local DC conductance in an important way. 

Once considered rare among sohds, fast ionic conduction has been found characteristic of hundreds of compounds. R.V Kumar and H. Iwahara discuss the science and application of these rare-earth superionic conductors as solid electrolytes. Conduction by oxygen and fluorine anions as well as hydrogen and other cations associated with these electrolytes are emphasized. They deal with extrinsic and intrinsic types together with their associated structures and structural types including structural defects. They conclude by outlining the many phcations of these solid electrolytes. 

K. Funke, S. Bruckner, C. Cramer, and D. Wilmer [2002] Dynamics of Mobile Ions in Solid Electrolytes—Conductivity Spectra and the Concept of Mismatch and Relaxation, J. Non-Cryst. Solids 307-310, 921-929. 

In disordered solid electrolytes, conductivity spectra taken at different temperatures typically show a gradual transition from one universality to the other, as seen in the example of Fig. 4. 

Fig. 7.4 Potential profiles in a solid electrolyte conducting oxygen ions and at the contact with the metal (left and right of the frame) in the stationary state of an EMF measurement (oxygen concentration cell). By virtue of the high carrier density Ho -is constant in the electrolyte and /ig-in the metal and have been set arbitrarily here. All other potentials are obtained from the equilibrium conditions (see Eq. (7.8)). In order to define Jle-1 fte- o in the solid electrolyte, it is necessary that an (very small) electron conductivity be taken into account (see Section 7.2.2 and Fig. 7.7). Likewise in order to define /lO) Mo - 3tnd fiQ - in the contact metal it is necessary there to take account of a low oxygen conductivity. The difference in oxygen potential is assumed, for simplicity, to be so small that the specific conductivities can be considered to be constant (cf. Eq. (7.1)). (Space charge zones are regarded as negligible.)...

M.p. 296 C. Accepts an electron from suitable donors forming a radical anion. Used for colorimetric determination of free radical precursors, replacement of Mn02 in aluminium solid electrolytic capacitors, construction of heat-sensitive resistors and ion-specific electrodes and for inducing radical polymerizations. The charge transfer complexes it forms with certain donors behave electrically like metals with anisotropic conductivity. Like tetracyanoethylene it belongs to a class of compounds called rr-acids. tetracyclines An important group of antibiotics isolated from Streptomyces spp., having structures based on a naphthacene skeleton. Tetracycline, the parent compound, has the structure ... 

Mott N F and M J Littleton 1938. Conduction in Polar Crystals. I. Electrolytic Conduction in Solid Salts. Transactions of the Faraday Society 34 485-499. 

Solid Electrolyte Systems. Whereas there has been considerable research into the development of soHd electrolyte batteries (18—21), development of practical batteries has been slow because of problems relating to the low conductivity of the soHd electrolyte. The development of an all sohd-state battery would offer significant advantages. Such a battery would overcome problems of electrolyte leakage, dendrite formation, and corrosion that can be encountered with Hquid electrolytes. 

Fig. 5. Conductivity as a function of temperature for some highly conducting solid electrolytes, where X in CuX is Cl, Br, or I (11).

Figure 5.3 The dependence of the conductivity of typical solid electrolytes on the oxygen pressure, showing the limits of electrolytic behaviour where t o is very close to unity...

The electrical conductivities of the solid electrolytes vaty over approximately two orders of magnitude, in the sequence Bi > Ce > Zr > Th... 

An instructive use has been made of the solid electrolyte, Agl, which conducts by the migration of silver ions. If this material is used as an electrolyte in the cell... 

The electrical conductivity also increases with increasing metal oxide content, due to the high mobility of the metal ions. For example several glass compositions have been used as solid electrolytes in galvanic cells in which other metal ions apart from the alkaline and alkaline earth ions have been incorporated. The electrochemical cell... 

A completely separate family of conducting polymers is based on ionic conduction polymers of this kind (Section 11.3.1.2) are used to make solid electrolyte membranes for advanced batteries and some kinds of fuel cell. 

Increasing numbers of advanced batteries for all purposes depend on ionically conducting solid electrolytes, so it will be helpful to discuss these before continuing. It should be remembered that any battery can be described as an electron pump, and the role of the electrolyte is to block the passage of electrons, letting ions through instead. 

Typical dimensions for the /5-alumina electrolyte tube are 380 mm long, with an outer diameter of 28 mm, and a wall thickness of 1.5 mm. A typical battery for automotive power might contain 980 of such cells (20 modules each of 49 cells) and have an open-circuit voltage of lOOV. Capacity exceeds. 50 kWh. The cells operate at an optimum temperature of 300-350°C (to ensure that the sodium polysulfides remain molten and that the /5-alumina solid electrolyte has an adequate Na" " ion conductivity). This means that the cells must be thermally insulated to reduce wasteful loss of heat atjd to maintain the electrodes molten even when not in operation. Such a system is about one-fifth of the weight of an equivalent lead-acid traction battery and has a similar life ( 1000 cycles). 

Sodium-Sulfur Batteries. The sodium-sulfur battery consists of molten sodium at the anode, molten sulfur at the cathode, and a solid electrolyte of a material that allows for the passage of sodium only. For the solid electrolyte to be sufficiently conductive and to keep the sodium and sulfur in a liquid state, sodium-sulfur cells must operate at 300°C to 350°C (570°F to 660°F). There has been great interest in this technology because sodium and sulfur are widely available and inexpensive, and each cell can deliver up to 2.3 volts. 

Electrolyte a substance, liquid or solid, which conducts electrical current by movement of ions (not of electrons). In corrosion science, an electrolyte is usually a liquid solution of salts dissolved in a solvent, or a molten salt. The term also applies to polymers and ceramics which are ionically conductive. 

This relationship makes it possible to calculate the maximum ionic conductivity of solid electrolytes. Assuming that the mobile ions are moving with thermal velocity v without resting and oscillating at any lattice site, this results in a jump frequency... 

Making use of Eq. (25), the maximum conductivity of a solid electrolyte with monovalent mobile species is given by... 

Generally, solid electrolytes for battery applications require high ionic conductivities and wide ranges of appropriate thermodynamic stability. 

Though solid electrolytes for multivalent ions offer the advantage of a larger charge transfer, their conductivities are much lower than those of monovalent ions at ambient temperature because of a higher activation enthalpy for the ionic motion... 

Another way of looking at high ionic conductivities of solid electrolytes is to consider the activation enthalpy as illustrated in Fig. 8. Generally, the activation enthalpy is strongly correlated with the room-temperature ionic conductivity the higher the room-temperature ionic conductivity, the lower the activation enthalpy. The straight lines in the Arrhenius... 

---