LISICON materials

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). 

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... 

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. 

---