Lithium ion conductivity of halides with a defect spinel structure

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Ionic conductivity is one of the functional properties of material. The preparation of the new materials having high ionic conductivity is a key technology for the development of fuel cell or secondary battery. In this research, solid electrolytes having the formula LiInBr_4 and Li_3InBr_6 were prepared and their structures and conduction mechanisms were investigated on the basis of high resolution X-ray diffraction and solid state NMR.Both of these structures could be regarded as a rock salt type in which three Li^+ is replaced by one In^<3+> and two vacancies. Although cubic LiInBr_4 belongs to a defect spinel structure, its structure can be regarded as a defect rock salt type because tetrahedral site is empty. Since the positional disorder of In^<3+> was commonly observed at the superionic state, this disorder plays an important role for the Li^+ conduction. Furthermore, a continuous solid solution Li_<1-x>,In_<x/3>Br, between LiBr and InBr_3 was suggested at least below x<0.2.