NASICON materials

As in 3 alumina, the sodium in NASICON can be replaced with other ions [60]. The conductivity increases with increasing silicon content, and the maximum conductivity occurs at a composition of about Na3Zr2PiSi2Oi2 (x 2) [61, 62]. The conductivities of some NASICON materials are shown with the ranges of conductivities for YSZ and 3 alumina in Figure 13.5 [63-68]. 

One of the typical examples is NASCION compound (Fig. 9.1), an acronym for A/d mper /on conductor. Before attracting interest as a cathode-active material, NASICON has a long research history of over 20 years as a solid electrolyte. Since Dehnas reported - that while LiTi2(PO )3 works as a lithium intercalation host and NaTi3(PO )3 works as a Na intercalation host, many attractive cathodes have been proposed based on the NASICON material group. 

As well as the solid solution formula given above, there have been suggestions that compositions off the join may also give single-phase NASICON. Part of the problem in determining solid solution stoichiometries and limits in materials such as NASICON arises because of the... 

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... 

A number of researchers, ° ° particularly in Japan, have been pursuing the oxides of iron as potential cathode materials for lithium cells. However, materials of the type LiFeOz have shown little ability for lithium removal. A number of other iron compounds have been studied over the years, including FeOCl, ° FePS3, ° KFeSz, and FeSz, but none showed much reversibility. Although metal phosphates have been studied for more than 20 years since the discovery of fast ion transport in NASICON, it is only recently that they have been considered as cathodes or anodes " of lithium batteries. 

Recently, LiFeP04, which adopts the olivine structure, has been widely studied as a possible cheap cathode material.Although the specific capacities of this material and the related NASICON structures are relatively low (typically 100 mAhg ), these compounds are cheap and open up new avenues for research. Li MAS NMR studies of a series of olivines LiMP04 with M = Mn, Fe, Ni, and Co were carried out by Tucker et A single resonance with large... 

A novel LiNiV04 positive material, having a voltage of approximately 4.8 with respect to Li, has been characterized and proposed for high voltage lithium ion batteries. However, its practical use may be limited by the lack of electrolytes capable of withstanding its high oxidation potential. Other recent developments include NASICON-related framework structures, such as a Fe2(S04)3-based compound. 

Other crystalline sodium ion conductors, the so-called NASICON compounds of general formula Na1+JCSiJtZr2P3 JtO 2 for 1.8 [Pg.251]

Reversible electrochemical lithium deintercalation from 2D and 3D materials is important for applications in lithium-ion batteries. New developments have been realized in two classes of materials that show exceptionally promising properties as cathode materials. The first includes mixed layered oxides exemplified by LijMn Nij, Co ]02, where the Mn remains inert to oxidation/reduction and acts as a framework stabilizer while the other elements carry the redox load. Another class that shows much potential is metal phosphates, which includes olivine-type LiFeP04, and the NASICON-related frameworks Li3M2(P04)3. 

Appreciable ionic conductivity is found in open framework or layered materials containing mobile cations (see Ionic Conductors). Several phosphates have been found to be good ionic conductors and are described above NASICON (Section 5.2.1), a-zirconium phosphates (Section 5.3.1), HUP (Section 5.3.3), and phosphate glasses (Section 5.4). Current interest in lithium ion-conducting electrolytes for battery apphcations has led to many lithium-containing phosphate glasses and crystalline solids such as NASICON type titanium phosphate being studied. ... 

FIGURE 12.12 Examples of FGM CMCs (left) the combination of NLM Nicalon SiC fiber reinforced zirconia (in white) and mullite (in black) matrices (right) a Nasicon matrix reinforced with mullite (Nextel) and SiC (NLMTM) fibers (see the sketch). (Reprinted from Colomban, R, Process for fabricating a ceramic matrix composite incorporating woven fibers and materials with different compositions and properties in the same composite, Mater. TechnoL, 10, 89, 1995. With permission.)... 

The measurement of local mechanical properties is an important step in understanding of the macroscopic behavior of multiphase materials. The indentation hardness test is probably the simplest method of measuring the mechanical properties of materials. Figure 12.2b shows the evolution of the microhardness as a function of the thermal treatment temperature of a Nasicon sample. The use of load-controlled depth-sensing hardness testers which operate in the (sub)micron range enables the study of each component of the composite more precisely. 

Padhi, A.K., Manivannan, V., and Goodenough, J.B., Tuning the position of the redox couples in materials with NASICON structure by anionic substitution, J. Electrochem. Soc., 145, 1518, 1998. 

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