Li Diffusion in Thin-Film Li_ySi Electrodes: Galvanostatic Intermittent Titration Technique and Tracer Diffusion Experiments

Li y Si is an interesting material for negative electrodes in Li-ion batteries. We carried out measurements with a galvanostatic intermittent titration technique (GITT) on ion-beam-sputtered amorphous Li y Si ( y ≈ 0.02 and 0.25) films to determine Li diffusivities at room temperature. The results are compared to Li tracer diffusion experiments conducted in our laboratory by secondary ion mass spectrometry (SIMS). SIMS measurements yield Li diffusivities several orders of magnitude lower than GITT measurements for Li 0.02 Si films. In contrast, both methods give a diffusivity of about 10 –20 m 2 /s for Li 0.25 Si films. The results can be explained by a heterogeneous electrochemical lithiation mechanism of the electrode material.