ELECTROCHEMICAL AND IN-SITU X-RAY-DIFFRACTION STUDIES OF THE REACTIONOF LITHIUM WITH TIN OXIDE COMPOSITES

We report our electrochemical and in situ x-ray diffraction experiment s on a variety of tin oxide based compounds; SnO, SnO3, LiSnO3, and Sn SiO3 glass, as cathodes opposite lithium metal in a rechargeable Li-io n coin cell. These materials, demonstrate discharge capacities on the order of 1000 mAh/(g Sn), which is consistent with the alloying capaci ty limit of 4.4 Li atoms per Sn atom, or 991 mAh/(g Sn). These materia ls also demonstrate significant irreversible capacities ranging from 2 00 mAh/(g active) to 700 mAh/(g active). In situ x-ray diffraction exp eriments on these materials show that by introducing lithium, lithium oxide and tin form first, which is then followed by the formation of t he various Li-Sn alloy phases. When lithium is removed the original ma terial does not reform. The ending composition is metallic tin, presum ably mixed with amorphous lithium oxide. The oxygen from the tin oxide in the starting material bonds irreversibly with lithium to form an a morphous Li2O matrix. The Li-Sn alloying process is quite reversible; perhaps due to the formation of this lithia ''matrix'' which helps to keep the electrode particles mechanically connected together.