Nasicon Family

Very similarly, the Naj xHf2Si, P3, eO 2 system [140, 141] shows maximum volume, minimum and maximum conductivity at % = 2.2. An additional NASICON analogue is Phoscan, Na3Sc2P3Oi2 however, the polymorphism of this is more complex and dependent on the processing conditions [2, 142-145]. 

---

Other ceramic ion conductors similar to /3-alumina were introduced by Goodenough et al in 1976 they belong to the so-called Nasicon family. Nasicon is a solid solution of the composition Na3Zr2Si2P012, exhibiting a Na+ conductivity of 0.2 S/cm at 300°C. Numerous Nasicon derivatives,... 

Sodium ion conduction in /S"-alumina is anisotropic and ceramic electrolytes produced from this material not only can be sensitive to exposure to moisture but also are somewhat difficult to densify (e.g., because of problems related to NaaO evaporation, conversion to single-phase / -alumina, and control of exaggerated grain growth). For these reasons. Serious attempts have been made to find alternative materials that have Na" ion conductivities comparable to or higher than / "-alumina but are easier and/or potentially more economical to fabricate. Here we review attempts to develop alternatives. They fall into two classes of materials the crystalline NASICON family of compounds and conducting glasses. 

This atomic arrangement results in a hexagonal skeleton of space group Ric with large structural vacancy sites per unit cell of octahedral symmetry (Ml) occupied by cations with the coordination number [6] such as titanium or zirconium and trigonal-prismatic symmetry (M2) occupied by vacancies as in Nb2(P04)3, by two-valent ions as in Ca05Ti2(PO4)3 or three-valent ions as in Lao, 33Ti2(P04)3. These vacancies account for the structural variability of the NASICON family as well as their ionic conductivity. 

Figure 7.21 Orthorhombic crystal structure of Li3Sc2(PO4)3 (Pbcn) alSOO C [209], (I) A M2T3O6O12/2 lantern , a common building block of NASICON and Li3M2(PO4)3 family (II) A fragment of Sc2(PO4)3 framework the shaded and unshaded areas are identical lanterns in...

NASICON is a family of high-conductivity Na conducting solid electrolytes, described in the previous chapter. The NASICON structure has a three dimensional network, where PO4 tetrahe-dra and Zr06 octahedra are linked by shared oxygens. The first report on trivalent cation conduction in a NASICON-type solid was for Sci/3Zr2(P04)3 obtained by a sol-gel... 

Crystalline inorganic electrolytes for Li-ion batteries can be divided into four main families of compounds, depending on their crystal strucmre (1) A-site deficient perovskite-type Li-ion conductors (2) Garnet-type Li-ion conductors (3) NASICON-type Li-ion conductors (4) LISICON-type Li-ion conductors. 

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... 

Recently, the concept of inductive effect have been applied to replace (P04) for (804) in polyanionic cathode materials [35, 36, 93-119]. Table 8.3 summarizes the structural properties of some fluorosulfate compoxmds. The fluorosulfates LLMSO4F constitute a wide family showing a good mix of properties, especially, both electrochemical and safety issues. However, we notice that the electroactive compounds appeared only in 2010 after the synthesis of newest member of the tavorite family LiFe (S04)F [36]. For instance, a simple substitution in Nasicon Li cM3(X04)3 networks increases the redox potential by 800 mV independently of the 2>d transition-metal ion [2]. Recent review by Rousse and Tarascon [119] deals with the crystal chemistry and structural-electrochemical relationship of new fluorosulfate polyanionic LiMS04p electrode materials. The lithiated fluorosulfates present an interesting family from the view point of crystal chemistry with the three main types of structure that depend on the nature of the transition-metal ion ... 

LiaN is another excellent two-dimensional conductor, but unfortimately it is very reactive [360]. Nasicon is an acronym for a family of excellent sodium ion conductors... 

---