Ion conduction

Ion movement can make a major contribution to o, particularly if the material has a large Eg. Conductivity resulting from ion migration is important in several ceramics. It is also the major conduction mechanism in ionic salts such as the halides. 

When we describe the mobility of ions we often use the absolute mobility, B  

The absolute mobility, and hence o, is directly related to the diffusion coefficient, D, through the Nernst-Einstein equation  

The diffusion coefficient is given by an Arrhenius equation, which means that there is an activation energy that must be overcome for the ions to move through the material as illustrated in Eigure 30.20. We can 

FIGURE 30.20 Potential energy barrier to ion movement, (a) In the absence of an applied field and (b) with an applied field. a is the activation energy and a the jump distance between ion sites. 

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Figure Bl.19.40. The scanning ion-conductance microscope (SICM) scans a micropipette over the contours of a surface, keepmg the electrical conductance tlirough the tip of the micropipette constant by adjusting the vertical height of the probe. (Taken from [211], figure 1.)...

Flansma P K, Drake B, Marti O, Gould SAC and Prater C B 1989 The scanning ion-conductance microscope Science 243 641... 

AHopregnanolone and similar A-ring-reduced pregnanes potentiate GABA effects at these receptors. These steroids mimic the effects of the benzodiazepines, changing chloride ion conductance and producing sedative and hypnotic behavioral effects (276,277). Neuroactive steroids can be therapeutically useful as anticonvulsants, anxiolytics, or anesthetics (qv) (see also Hypnotics, sedatives, anticonvulsants, and anxiolytics). 

X-ray fluorescence, mass spectroscopy, emission spectrography, and ion-conductive plasma—atomic emission spectroscopy (icp—aes) are used in specialized laboratories equipped for handling radioisotopes with these instmments. 

Fast-Ion-Gonducting Glasses. One possible appHcation of fast-ion-conducting glasses is in soHd-state batteries (qv) for automobiles. The glasses might also be used in electrochromic displays or as sensors (qv) (25). 

Ion channels combine ion selectivity with high levels of ion conductance... 

Each porin molecule has three channels Ion channels combine ion selectivity with high levels of ion conductance The K+ channel is a tetrameric molecule with one ion pore in the interface between the four subunits... 

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). 

The first use of ionic liquids in free radical addition polymerization was as an extension to the doping of polymers with simple electrolytes for the preparation of ion-conducting polymers. Several groups have prepared polymers suitable for doping with ambient-temperature ionic liquids, with the aim of producing polymer electrolytes of high ionic conductance. Many of the prepared polymers are related to the ionic liquids employed for example, poly(l-butyl-4-vinylpyridinium bromide) and poly(l-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide [38 1]. 

The external set-up of different battery systems is generally simple and differs in principle only little from one system to another. A mechanically stable cell case bears the positive and negative electrodes, which are separated by a membrane and are connected with electron-conducting poles. Ion conduction between the electrodes is guaranteed usually by fluid or gel-like electrolyte [13]. 

The deposition points on the lithium electrode are the points at which the protective film has a higher lithium-ion conductivity. One example of these deposition points are the pits on the lithium anode caused by discharge. Crystalline defects and the grain boundaries in lithium may also initiate deposition. 

This section reports on the current state of knowledge on nonaqueous electrolytes for lithium batteries and lithium-ion batteries. The term electrolyte in the current text refers to an ion-conducting solution which consists of a solvent S and a salt, here generally a lithium salt. Often 1 1-salts of the LiX type are preferred for reasons given below only a few l 2-salts Li2X have attained some importance for batteries, and 1 3-salts Li3X are not in use. 

Purification of solvents and salts is essential for reliable electrochemical studies and measurements. A water content of 20ppm already corresponds to a 10 3molL solution. This is in the concentration range of dilute solutions used in conductivity studies for the determination of association constants (see Sec.7.3.2). Traces of water may affect chemical equilibria and therefore act on specific conductivities and limiting ion conductivities. For example, addition of 30 ppm water to a 2xl0-4 mol LT1 solution of LiBF4 in THF at 15 °C increases its conductivity by 4.4 percent (precision of measurements about 0.02 percent) 380 ppm water causes an increase by 51.7 percent see Fig. 3 [20J. 

It is worth mentioning that single-ion conductivities of lithium ions and anions at infinite dilution, and transference numbers of ligand-solvated lithium ions estimated therefrom, increase due to the replacement of more than one (generally four) solvent molecules. Table 6 demonstrates this beneficial feature. 

Table 6. Single-ion conductivities of solvated lithium ions and anions at 25 °C in PC at infinite dilution [13]...

There is a difference in the behavior of benzenediolatoborate and naphthalenedio-latoborate solutions on the one hand, and lithium bis[2,2 -biphenyldiolato(2-)-0,0 ] borate (point 5 in fig. 8) lithium bis[ sali-cylato (2-) Jborate (point 6) or benzene-diolatoborate/phenolate mixed solutions on the other (Fig.8). This can be tentatively explained by the assumption of different decomposition mechanisms due to different structures, which entail the formation of soluble colored quinones from benzenediolatoborate anions and lithium-ion conducting films from solutions of the latter compounds (points 5 and 6) [80], The assumption of a different mechanism and the formation of a lithium-ion conducting, electronically insulating film is supported by... 

Figure 10 shows the voltage windows of chelatoborates. The question mark ( ) indicates the formation of lithium-ion conducting films, preventing the electrolyte from decomposition the numbers refer to the compounds mentioned in this section of the text. 

Conductivities k of electrolytes are related to molar conductivities A, ion conductivities A, and ionic mobilities w(- by Eq. (57)... 

Addition of both ion-conducting and inert ceramics enhances the conductivity of a polymer electrolyte. This increase is attributed to an increase in volume fraction of the amorphous phase [133-136]. No... 

The co-precipitation technique starts with an aqueous solution of nitrates, carbonates, chlorides, oxychlorides, etc., which is added to a pH-controlled solution of NH4OH, allowing the hydroxides to precipitate immediately. This method requires water-soluble precursors and insoluble hydroxides as a final product. The hydroxides are filtered and rinsed with water when chlorides are employed as starting materials and chlorine is not desired in the final product. After drying the filtrate, it is calcined and sintered. This method is being applied very successfully for oxygen-ion conducting zirconia ceramics [30],... 

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