| dc.description | Tin oxide composite (SnO:X, X = (B2O3)x(P 2O5)y, SiO2) glasses represent a new class of material for the anode of lithium-ion rechargeable cells. These materials demonstrate discharge capacities on the order of 1000 mAh/(g Sn), which is consistent with the alloying limit of 4.4 Li atoms per Sn atom. These materials also demonstrate significant irreversible capacities, which is proportional to the oxygen content (i.e., O in SnO:X). It is shown (by electrochemical data, in-situ x-ray diffraction studies and in-situ Mossabuer effect studies) that during the first discharge, the oxygen intimately bonded to Sn reacts with lithium to give Li2O, leaving small clusters of metallic Sn that subsequently alloy with lithium. The Li2O and X atoms (collectively known as 'Spectator Atoms') are inert to lithium. The subsequent cycling, or reversibility, of these materials is linked to the size of the Sn clusters that form during the first discharge. Those materials with high spectator atom count (as in SnO:(B2O3 )0.5(P2O5)0.5 glass) produce smaller Sn clusters during first discharge than those materials with low spectator atom count (as in SnO:(B2O3)0.1(P2O 5)0.l glass). Furthermore, it is observed that these Sn clusters grow in size by the repeated discharge and charge of the cell. This explains the capacity loss in these types of materials after many cycles. The size of the Sn clusters reach a steady state size, and a speculative model that links the steady state cluster size to the number of spectator atoms is proposed. The rate of aggregation of Sn clusters can be controlled by several factors: the voltage range chosen for discharge and charge, the number of spectator atoms in the matrix, and the temperature. Studies of other alloying metal oxide composites (i.e., PbO:X and Sb2O3:X) are also presented. These materials follow a similar reaction mechanism as SnO:X composites do, but the rate of aggregation of the alloying metal differs between all three. | en_US |
