Deeper insight on the lithium reaction mechanism with amorphous tin composite oxides

Lithium reaction mechanism in amorphous tin composite oxide SnB0.6P0.4O2.9 is characterized by X-ray diffraction, Sn-119 Mossbauer spectroscopy and X-ray absorption fine structure. The analysis of the experimental data concerning SnB0.6P0.4O2.9 shows that Sn-II is highly ionic and is surrounded by three oxygen atoms. The detailed analysis of lithium insertion mechanism shows a complex reduction mechanism in two steps. During the first one the main reaction corresponds to a partial Sn-II reduction, involving a mixed valence system. It is accompanied by modifications of tin environments, while lithium acts as a network modifier inducing the formation of nonbridging oxygen atoms. The second step corresponds to Li-Sn alloying process, with the formation of Li-Sn bonds. It is worth noting the persistence of Sn-O interactions in this second step. The reversible part of the mechanism can be explained from the formation of small particles of lithium-tin alloys in strong interaction with the oxygen atoms in the glass matrix, while the vitreous support presents an interesting dispersal effect. (C) 2003 Elsevier SAS. All rights reserved.