Li-ion diffusion behavior in Sn, SnO and SnO2 thin films studied by galvanostatic intermittent titration technique

Poorly crystallized Sn, SnO and amorphous SnO2 thin films have been prepared by radio frequency magnetron sputtering on Cu substrates and have been characterized by X-ray diffraction, scanning electron microscope and Raman spectra. The electrochemical performance of the thin films has been studied by galvanostatic cycling and cyclic voltammetry. The apparent Li-ion chemical diffusion coefficients, D̃Li, of the films have been determined by galvanostatic intermittent titration technique (GITT). It is found that the D̃Li values by GITT are in the range of 10− 16 to 10− 14 cm2 s− 1 for the metallic Sn film and 10− 15 to 10− 13 cm2 s− 1 for the tin oxide films. The improved Li-ion diffusion rate in the oxide films than in the metal film is due to its unique microstructure formed during the first cycle, namely, a uniform dispersion of LiδSn (0 ≤ δ ≤ 4.4) in the Li2O matrix.