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

We report our electrochemical and in situ x‐ray diffraction experiments on a variety of tin oxide based compounds; SnO, , , and glass, as cathodes opposite lithium metal in a rechargeable Li‐ion coin cell. These materials 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, presumably mixed with amorphous lithium oxide. The oxygen from the tin oxide in the starting material bonds irreversibly with lithium to form an amorphous 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.