Pressure-Sensitive Modeling of the Reversible Lithiation of Vacant Thiospinel (In0.50.5)[In1.5Sn0.5]S4

A simple atomic model is described in which lithiation appears as a reversible pressure acting on confined atomic species which constitute the host material. It is demonstrated, by ab initio calculations of the properties of a confined atom as a function of the cavity radius, that the ionization of Sn occurs in the manner which has been observed, i.e., it passes directly from SnIV to SnII without the appearance of SnIII. This is shown not to be the case for a confined atom with no d shell present, and therefore we conclude that the observed property is of atomic origin and is directly related to the high compressibility of d orbitals. Extensions of our model are suggested to include relativistic effects, which would enable ab initio calculations of the M?ssbauer signals to be attempted for the lithiated compounds. This would provide an independent test of our model.