Lithium Tracer Diffusion in Amorphous LixSi for Low Li Concentrations

Li tracer self-diffusion was studied in amorphous lithium–silicon compounds which are important as negative electrodes in Li-ion batteries. Experiments were done on LixSi/6LixSi (LixSi, x ∼ 0.02 and x ∼ 0.06) thin-film heterostructures using secondary ion mass spectrometry. The diffusivities follow the Arrhenius law in the temperature range between 140 and 325 °C, both with an activation energy of (1.42 ± 0.03) eV, while the Li-richer samples show 1 order of magnitude higher diffusivities. A trap-limited diffusion mechanism is suggested, explaining this result with a lower concentration of unsaturated traps. A discussion against the literature suggests a strong lithium concentration dependence of diffusivities also for higher x.