NASICON MATERIALS - A LONG NEGLECTED CLASS OF SOLID ELECTROLYTES

摘要

The so-called NASICON materials AT_2P_3O_(12) (A = alkaline metal, T = tetravalent transition metal) are known since the 1970s [1] and are derived from the first "Na~+ super-ionic conductor", Na_3Zr_2Si_2PO_(12), of this group of materials. The aims of current investigations are on the one hand the better understanding of the ionic conduction and on the other hand the search for new materials with very high ionic conductivity. For this purpose, new and simple synthesis methods have been developed, which deliver very homogeneous powders with reduced temperatures for the preparation of ceramics. In this way a lithium ion conductor with the composition Li_(1.5)Al_(0.5)Ti_(1.5)P_3O_(12) was manufactured. After sintering to highly dense ceramics a total conductivity of 0.7 mS/cm was achieved at room temperature [2] and therefore this material belongs to the best known solid oxidic Li~+ ion conductors. NMR and impedance spectroscopy investigations [3-5] have shown that the bulk conductivity amounts to 3-5 mS/cm and that the grain boundaries determine the quality of the material.