Solid NMR Study of Lithium Ions Accommodated in Various Transition Metal Oxides

Abstract

Solid NMR was used to elucidate the lithium accommodation/extraction reaction in various transition metal oxides. The first study was the lithium ion exchange reaction of titanium antimonic acid (TiSbA). The effect of hydration on the selectivity of lithium ion in the solid phase was examined using ⁷Li NMR. The second study was the irreversible ion exchange behavior of HNbO₃. The selectivity for the lithium ion and the irreversible behavior were examined using ¹H and ⁷Li NMR. The third study was the isotope separation between ⁶Li and ⁷Li in various inorganic ion exchangers. The high isotope separation coefficient was ascribed to the degree of dehydration during the ion exchange reaction. The degree of dehydration was examined by ¹H and ⁷Li NMR studies. The last study was determining the mechanism of the lithium accommodation/extraction reaction of λ-MnO₂ in an aqueous solution. The different paths between the accommodation and extraction and the formation of MnO₄⁻ during the accommodation were determined by chemical analysis. The Knight shift in the ⁷Li MAS-NMR spectra of Li_0.5MnO₂ suggested the localization of the electron density on the lithium nuclei. An XPS study also suggested the presence of an electron density on the lithium nuclei. A pH-independent redox couple was assumed to account for the accommodation/extraction reaction of lithium ions, such as Li(I)/Li(0).