Electrochemical and In Situ XRD Studies of the Li Reaction with Combinatorially Sputtered Mo[sub 1−x]Sn[sub x] (0 ≤ x ≤ 0.50) Thin Films

Abstract

Detailed electrochemical studies of the reaction of Li with combinatorially sputter-deposited BCC and nanocrystalline thin films are reported for In situ X-ray diffraction (XRD) performed for 0.36, 0.44, show no evidence for formation of new phases during the reaction with Li. During charge/discharge cycling, a definite and periodic variation of the BCC (110) Bragg angle for is strong evidence for a topotactic Li insertion mechanism. Sensitive differential capacity vs. measurements on cells with show no new peaks for as many 75 cycles, supporting a topotactic insertion reaction. However, in the higher Sn content films the appearance and growth of new peaks after the first cycle is consistent with the aggregation of Sn clusters and the formation of Li-Sn phases. Inclusion of about 20% oxygen in nanostructured films seems to prevent Sn aggregation and improve the cycling performance markedly. The best materials give specific capacities near 350 mAh/g, have densities near 9 g/cc and cycle well. This could be the first report of true topotactic Li insertion into a metal host. © 2004 The Electrochemical Society. All rights reserved.