Mechanochemical synthesis of Sn1-xMoxO2 anode materials for Li-ion batteries

Sn1-xMoxO2 mixed oxides of low crystallinity have been synthesized by mechanical milling of the starting elements in an air atmosphere at room temperature and investigated as electrode materials for lithium batteries. The oxides were characterized by X-ray diffraction, infrared spectroscopy and X-ray photoelectron spectroscopy. The results suggest that the Mo-doped samples are solid solutions with a cassiterite-type structure and Mo in the tetravalent oxidation state. Significant amounts of amorphous silica over the range 12-23% by weight as determined by energy dispersive analysis (EDX), and originating from the agate jar and balls of milling apparatus used for the experiments, were also detected. The compounds were tested as electrodes in secondary lithium batteries. The addition of Mo has two favourable effects, namely: (i) it increases the discharge capacity; and (ii) it improves capacity retention in cells cycled between 1.0 and 0.0 V. The formation of a Li-Mo-O oxide conductive matrix during the electrochemical insertion of lithium may account for this enhanced performance. In this reasoning, the silica present in the samples was assumed to play a minor role based on the stability of the Si-O bond.