Lithium Diffusion in Amorphous LixSi (x ≤ 0.4) Materials

Abstract

Lithium-silicon compounds are promising materials as negative electrodes in Li-ion-batteries. The diffusion of Li in electrode materials is important for charging/discharging rates, maximum specific capacity and possible side reactions. In order to further the development of novel negative electrode materials for lithium-ion batteries, understanding the basic principles of atomic transport is of high importance. Thin LixSi films were investigated, which were produced by reactive ion-beam co-sputtering of segmented elemental Li and Si targets. Li tracer self-diffusion experiments were done on LixSi|6LixSi heterostructures and6Li and7Li isotopes depth profiles were analysed by secondary ion mass spectrometry before and after annealing. Diffusivities were extracted by comparing the experimental depth profiles to analytical solutions of the diffusion equation. The diffusivities for low Li concentrationsx< 0.1 in LixSi follow the Arrhenius law between 140 and 325 °C with an activation energy of 1.4 eV. A trap-limited diffusion mechanism is suggested, comparable to hydrogen diffusion in hydrogenated amorphous silicon. In contrast, for x ≈ 0.4 complete isotope interdiffusion is observed directly after deposition at room temperature. These results indicate a significant acceleration of diffusion with increasing Li content as suggested in literature by theoretical calculations [1].