Electrochemical and In Situ X‐Ray Diffraction Studies of the Reaction of Lithium with Tin Oxide Composites

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We report our electrochemical and in situ x-ray diffraction experiments on a variety of tin oxide based compounds; SnO, Sn02, Li2SnO3, and SnSiO3 glass, as cathodes opposite lithium metal in a rechargeable Li-ion coin cell. These mate-rials demonstrate discharge capacities on the order of 1000 mAh/(g Sn), which is consistent with the alloying capacity limit of 4.4 Li atoms per Sn atom, or 991 mAh/(g Sn). These materials also demonstrate significant irreversible capacities ranging from 200 mAh/(g active) to 700 mAh/(g active). In situ x-ray diffraction experiments on these materials show that by introducing lithium, lithium oxide and tin form first, which is then followed by the formation of the various Li-Sn alloy phases. When lithium is removed the original material does not reform. The ending composition is metallic tin, pre-sumably mixed with amorphous lithium oxide. The oxygen from the tin oxide in the starting material bonds irreversibly with lithium to form an amorphous Li20 matrix. The Li-Sn alloying process is quite reversible; perhaps due to the for-mation of this lithia "matrix " which helps to keep the electrode particles mechanically connected together.