Sodium and lithium ion conductors

The fact that silver iodide is an ion conductor was first observed in 1914 by Tubandt and Lorentz. They noted that when a current was passed between Ag electrodes separated by solid Agl, the mass of the electrodes changed. At room temperature, Agl can exist in either the P- or y-form. On heating to 419 K, both phases transform to a-Agl, and this is accompanied by a dramatic increase in ion conductivity. In ot-Agl, the 1 ions are in a body-centred cubic arrangement. The Ag ions randomly occupy tetrahedral 

A solid oxide fuel cell consists of a cathode (at which O2 from the air is reduced to and an anode (at which H2 is oxidized), and an electrolyte. The cell operates at 1300K. Explain why stabilized zirconia Zr02 doped with CaO or Y2O3 is a suitable material for the electrolyte. What is the product at the anode  

Current developments in battery technology, electrochromic devices (see Box 22.4) and research into electrically powered vehicles make use of solid electrolytes (see Box 10.3). The sodium/sulfur battery contains a solid 3-alumina electrolyte. The name (3-alumina is misleading since it is prepared by the reaction of Na2C03, NaN03, NaOH and AI2O3 at 1770K and is a non-stoichiometric compound of approximate 

Na P-alumina can be replaced by cations such as Li+, K+, Cs+, Rb+, Ag, Tl and H+. However, the conductivities of these materials are lower than that of Na P-alumina the match between the size of the Na ions and the interlayer channels in the host lattice leads to the most efficient cation mobility. The conductivities of Na P-alumina and selected cation and anion conductors exhibiting relatively 

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Quite a large variety of interesting fast lithium-ion solid conductors is now known, as compiled in Fig. 9 and Table 1. In the case of sodium- and potassium-ion conductors only the / / / " -alumina fam-... 

Quite a large variety of interesting fast lithium-ion solid conductors is now known, as compiled in Figure 19.9 and Table 19.1. In the case of sodium-and potassium-ion conductors only the /l/)3"-alumina family, and for sodium the NASICON structure, were considered for practical application, due to the high ionic conductivities of these materials which are unmatched by any other sodium- or potassium-ion conductor. However, for 73/73"-alumina, NASICON and structurally related ionic conductors, the ionic conductivities and activation enthalpies are... 

Lithium carbonate can be used more directly as the auxiliary electrode with a lithium ion conductor, since the in situ formation of another carbonate phase is not required. Lithium ion conductors used with Li2CO3 include LISICON [163] and other Li3PO4-based electrolytes [164—173]. As with sodium ion conductors, Li2CO3-containing carbonates are used with lithium ion conductors [174, 175], The outputs of some examples of these lithium ion-conducting electrolyte-based sensors are shown in Figure 13.11 [163, 172-174]. 

In several cationic conductors, for example sodium-ion conductors based upon Na2S04 and perovskite-type lithium-ion conductors, rare-earth elements are important constituents, which directly or indirectly aid the ionic conduction in such solids. Somewhat unexpectedly, rare-earth elements in oxidation state (III), despite their large size and high charge, themselves may be the mobile component in solid electrolytes such as P-alumina, LaNb309 and Sc2(W04)3 oxides. 

It is also noteworthy that the ionic conductivity of a simple mixture of PEO and alkali metal salt was improved 10 to 100 times by employing larger cations such as sodium or potassium ions [17], whereas numerous lithium cation conductors are known to date. The improved ionic conductivity is attributed to the weaker... 

Many solid electrolytes are known today and it can be expected that their importance will further increase, especially for electrochemical devices. For example, beta-alumina solid electrolyte (BASE) is a fast ion conductor, which is used as a membrane in electrochemical cells. It can contain small ions like sodium, which show a high mobility. More classical examples are electrolytes based on lithium or silver iodide where the small cations are very mobile [13]. Note that solid polymer electrolytes are also a rapidly growing field [14]. 

For hthium, counterparts structurally related to the sodium and potassium and NASICON with similar high ionic conductivities were not found, possibly because of the small ionic radius of lithium. Therefore, much intensive work has been done on developing lithium-ion sohd conductors during recent years, in view of the interest in high-energy-density batteries. 

The Group 1 elements—lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr)—are called the alkali metals. The alkali elements are soft, silvery-white metals and good conductors of heat and electricity. Their chemistry is relatively uncomplicated they lose their s valence electron and form a 1 + ion with the stable electron configuration of the noble gas in the preceding period. 

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