On the aggregation of tin in SnO composite glasses caused by the reversible reaction with lithium

We show that the reaction mechanism in Li/[SnO:(B2O3)(x):(P2O5)(y) glass (0.1 less than or equal to x,y less than or equal to 0.5)], Li/[SnO: B2O3)(0.5):(P2O5)(0.5):(K2CO3)(0.04) glass] and Li/SnO cells is common. During the first discharge, the oxygen bonded to tin las SnO) reacts with lithium to give metallic tin (which can be present as clusters of a few atoms) and lithia. The tin reacts with further lithium to the composition limit of Li4.4Sn During charge the Li is removed from the lithium-tin alloy. The other components of the glass (e.g., B2O3, P2O5 Li2O, etc.) are inert with respect to lithium, and we call the atoms which make up these phases "spectator atoms." Using X-ray diffraction (XRD) and electrochemical methods, we show that size of the initial tin regions which form is inversely proportional to the spectator:Sn atom ratio. However, during cycling, all of these materials show the subsequent aggregation of the tin atoms into clusters which grow with cycle number until they reach a saturated size. The final cluster size is larger for materials with smaller X:Sn ratio. We propose a speculative model, which predicts the saturated Sn cluster size, asa function of the spectator:Sn ratio. (C) 1999 The Electrochemical Society. S0013-4651(98)04-068-3. All rights reserved.