Kinetics of Li insertion into polycrystalline and nanocrystalline 'SnSb' alloys investigated by transient and steady state techniques

Two different methods for studying the kinetics of electrochemical insertion of lithium into thick-film polycrystalline SnSb and thin-film nanocrystalline 'SnSb' alloys (nanocrystalline SnSb alloys with an excess of Sn as second phase) are presented. In each case, the composition dependence of the chemical diffusion coefficient has been obtained from galvanostatic polarization experiments on the asymmetric cell, Li \ 1 M LiClO4 in PC \ SnSb, with Li as additional reference electrode. Coulometric titrations were employed for composition variation with high stoichiometric resolution. Polycrystalline SnSb alloys have been prepared from the elements and incorporated as cathode into the cell. The chemical diffusion coefficient (D) over tilde as function of lithium content has been obtained from a combination of short-time transient and steady state measurements. Values of (D) over tilde for polycrystalline LideltaSnSb-alloys are in the range of 10(-10) cm(2) s(-1) at 25 degrees C. Alternatively, for the thin-film nanocrystalline 'SnSb' alloy, the short- and long-time approximation of the polarization voltage is used to obtain the chemical diffusion coefficients without taking into account the slope of the coulometric titration curve. The low (D) over tilde-value resulting for the nanocrystalline "SnSb' alloy ((D) over tilde < 4 X 10(-12) cm(2) s(-1)) may be attributed to its complex morphology as well as to the existence of additional Sn domains acting as diffusion barriers. (C) 1999 Elsevier Science S.A. Ail rights reserved.