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

Lithium reaction mechanism in amorphous tin composite oxide SnB_0.6P_0.4O_2.9 is characterized by X-ray diffraction, ¹¹⁹Sn Mössbauer spectroscopy and X-ray absorption fine structure. The analysis of the experimental data concerning SnB_0.6P_0.4O_2.9 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.