Abstract
Li-Ion or Na-Ion battery materials, positive electrodes and solid electrolytes in particular, are essentially inorganic compounds into which alkali metals (Li+ or Na+) must diffuse, more or less rapidly or reversibly. As such, they exhibit very interesting fundamental properties of phase transformation upon insertion/extraction of alkali ions, and also as a function of temperature. This provides the crystallochemist with a fantastic playground !
The NaSICON structure, whose remarkable sodium ion conduction properties were discovered over fifty years ago by J. B. Goodenough and his colleagues, is a remarkable example. With the general formula AxM2(XO4)3, it takes the form of an extremely stable three-dimensional " framework " of MO6 octahedra (M = Zr, Fe, V, Ti, Nb, Mn, Cr...) and XO4 tetrahedra (X = P, S, Si, W, Mo), which generate a three-dimensional space in which A+ ions (A = Li, Na) move (rapidly).
Depending on the nature of the elements placed in the octahedral and tetrahedral sites, the NaSICON structure thus offers a whole range of materials that can be used as electrodes, positive or negative, or as solid electrolytes, in sodium or lithium batteries.
In this talk, I'll look at a number of examples illustrating the versatility of this structure, enabling all-solid-state sodium batteries to be built with operating voltages and temperatures that can be controlled by the solid-state chemist.
