Lithium Distribution in Monocrystalline Silicon-Based Lithium-Ion Batteries

The ability of nitrides and alloys of refractory metals to act as solid-state diffusion barrier for Li migration in Si was evaluated by mass spectrometry techniques. Magnetron sputtered barrier films on silicon, assembled in a Swagelok (R) half-cell, were used as working electrodes to determine whether several barrier layers are able to prevent the formation of Li-Si alloys. In addition, lithium ion diffusion was studied in monocrystalline silicon. To determine the depth profiles in the silicon substrate and in the barrier layer, respectively, two complementary techniques, being based on mass spectrometry, were applied: (i) ToF-SIMS was used as imaging technique for depth profiling the first microns and (ii) laser ablation ICP-MS was carried out to study depth profiles of up to hundreds of microns. Titanium nitride as well as tantalum nitride barriers turned out to prevent or inhibit the reaction between lithium and silicon. Regarding Li diffusion in silicon preliminary tests were performed to investigate both diffusion coefficients and the activation energies in (100) monocrystalline silicon.