Electrochemistry of InSb as a Li insertion host problems and prospects

Ballmilling of In and Sb has been used to produce InSb for use in electrochemical and in situ X-ray diffraction studies (XRD) of Li/1 M LiPF6 ethylene carbonate:diethyl carbonate/InSb cells. The cell capacity decays rapidly when cycled between 0 and 1.3 V, while the capacity reduction is less pronounced when cycling is restricted to the 0.65-1.4 V range. In situ XRD studies reveal that Li3Sb and In are formed during the first plateau (above 0.65 V), according to the reaction 3Li + InSb --> Li3Sb + In. The indium product subsequently reacts with Li forming the InLix phases InLi and In4Li7 in sequence. When cells are cycled above 0.6 V (i.e., in the absence of InLix formation) capacity retention improves significantly, remaining relatively constant near 250 mAh/g. Detailed in situ XRD studies of these cells suggest that 0.27 Li atoms per InSb may be intercalated during a sharp drop in the cell potential, according to the reaction xLi + InSb reversible arrow LixInSb (x(max) = 0.27). This intercalation accounts for only a small (about 30 mAh/g) fraction of the overall capacity of 680 mAh/g. Consequently, it appears that the reactivity of In and Sb with Li, not the structure type, determines the reaction path. Therefore, InSb is not an attractive intercalation host for Li, in contrast to the claims made in the literature. (C) 2001 The Electrochemical Society.