LISICON

The lithium analogues of NASICON are, in fact, quite different materials (Irvine and West, 1989). They are solid solutions based on stoichiometric phases such as y-Li2ZnGe04 or y-Li3(P, As, V)04, but containing 

Li2 + 2xZni Ge04 0.3 x 0.8 (limits vary with temperature) 

The crystal structures of the end-members with x = 0 are so-called y-tetrahedral structures , with distorted hexagonal close packed oxide arrays and cations distributed over various tetrahedral sites. In the solid solutions, Li ions are found, by powder neutron diffraction, to occupy partially various tetrahedral and octahedral interstitial sites, which link up to form an essentially three-dimensional conduction pathway. 

Stoichiometric Li4SiQ4 is a modest Li ion conductor but is a very good host material for doping (Irvine and West, 1989). Both Li interstitials and Li vacancies can be created resulting in high conductivities. In the substitution. Si A1 -t- Li, the A1 ions occupy Si sites with Li entering interstitial sites, to give 

Alternatively, the substitution, 3Li Al, leads to the creation of Li vacancies, with the general formula 

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An interesting feature of the conduction mechanism in these materials and the LISICONS is that it is, at least partially, an interstitialcy mechanism. Both structure types contain examples of face-sharing tetrahedral sites. Fig. 2.13. Such sites are much too close together for both to be occupied simultaneously. Crystal structure refinements show that often, on average, one site of each pair contains a Li ion but the occupancy appears to be random. This means that, during conduction, one site of each pair may contain a Li ion but this is ejected when an incoming... 

Li" ion enters the adjacent, face-sharing site. It is clear that, in these materials, Li ions do not move by means of isolated, random hops in the LISICONS there is clear evidence for clustering of lithium ions and indeed, migration may involve a process of continual reorganisation of the clusters (Bruce and Abrahams, 1991). 

The use of framework structures to minimize AH for alkali-ion electrolytes has been demonstrated to provide a means of opening up the bottlenecks to cation motion in a number of oxides (Goodenough, Hong and Kafalas, 1976). Framework structures may provide one-dimensional tunnels as in hollandite, two-dimensional transport in planes as in the )S-aluminas, or three-dimensional transport as in NASICON and LISICON. Since one-dimensional tunnels are readily blocked, the two-and three-dimensional conductors are the more interesting. 

NASICON have been studied (Kohler Schulg, 1985). LISICON type FICs are found to show negative activation volumes at high pressures (Bose et al., 1984). 

Crystalline solid electrolytes such as a-Agl, ji-alumina, NASICON, and LISICON, LLN, oxide ion conductors such as yttria-stabilized zirconia, etc ... 

Figure 7.23 Crystal structure of LISICON Li3. 5Zno.25Ce04 [234]. Striped tetrahedra — CeO4 gray tetrahedra — (Li,Zn)O4 the white polyhedra are partially occupied by lithium. The structures of Li3.75Geo.75Vo.25O4 and Li3.70Ge0.85W0.15O4 [235] differ only in minor details.

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]. 

Menil, F., Daddah, B.O., Tardy, P., Debeda, H. and Lucat, C. (2005) Planar LiSICON-based potentiometric CO2 sensors influence of the working and reference electrodes relative size on the sensing properties. Sens. Actuators B, 107 (2), 695-7. 

According to the results in the bibUography, although the majority of the works use NaSICON for the electrolyte, LiSICON is an option to take into account because its cross-sensitivity to water can be better lowered. Moreover, this electrolyte material shows a greater detection range, as shown in Fig. 16.4 (Fergus, 2008). 

As well known, air electrodes in systems with aqueous solutions feature the best characteristics in alkaline solutions. Unfortunately, the LiSICON-type materials are destroyed and lose ionic conductivity in alkaline solutions. Therefore, using neutral solutions, particularly, buffer solutions containing acetic acid and lithium acetate in lithium-air batteries is suggested. Certainly, the processes on the positive electrode in this case are not described by Equations (13.1) and (13.4), but by equations... 

The development of organic or inorganic lithium-ion conductor such as lithium super-ion conducting glass (LISICON). lithium iodide (Lit), solid polymer electrolytes(SPE) were activated with progress of a lithium battery. In these electrolytes, the technology of solid electrolyte is useful to improve the performance of batteries. 

Murayama, M. Sonoyama, N. Yamada, A. Kanno, R., Material design of new Uthium ionic conductor, thio-LISICON, in the Li2S-P2S5 system, Solid State Ionics 2004,170,173-180. 

C. Conductivity of PolycrystaUine LISICON Li2+2 Zni jGe04 and a Model for Intergranular Constriction Resistances, J. Electrochem. Soc. 130, 662-669. 

Lisicon. The eompound Lij4Zn(Ge04)4, a fast ion conductor (q.v.). 

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