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 insertio n of lithium into thick-film polycrystalline SnSb and thin-film nanocrystal line 'SnSb' alloys (nanocrystalline SnSb alloys with an excess of Sn as sec ond phase) are presented. In each case, the composition dependence of the c hemical diffusion coefficient has been obtained from galvanostatic polariza tion 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. Polycrystal line SnSb alloys have been prepared from the elements and incorporated as c athode into the cell. The chemical diffusion coefficient (D) over tilde as function of lithium content has been obtained from a combination of short-t ime transient and steady state measurements. Values of (D) over tilde for p olycrystalline LideltaSnSb-alloys are in the range of 10(-10) cm(2) s(-1) a t 25 degrees C. Alternatively, for the thin-film nanocrystalline 'SnSb' all oy, the short- and long-time approximation of the polarization voltage is u sed to obtain the chemical diffusion coefficients without taking into accou nt the slope of the coulometric titration curve. The low (D) over tilde-val ue 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) 1 999 Elsevier Science S.A. Ail rights reserved.