# Lithium Diffusion in Amorphous Lithium-Silicon

Harald Schmidt¹,², Florian Strauß²

¹ Clausthaler Zentrum für Materialtechnik, Technische Universität Clausthal, Leibnizstr. 9, 38678 Clausthal-Zellerfeld, Germany; ² Institut für Metallurgie, Technische Universität Clausthal, Robert-Koch-Str. 42, 38678 Clausthal-Zellerfeld, Germany

E-Mail: strauss.florian@tu-clausthal.de

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. Amorphous silicon is a very interesting high-capacity negative electrode material for innovative applications. Amorphous lithium-silicon (LiₓSi) is formed during lithiation of silicon electrodes but can also be directly used as electrode material. In both cases the lithium diffusion properties influence the achievable (dis-)charging rates, the maximum capacity and the mechanical stress formation.

Thin LiₓSi films were investigated, which were produced by ion-beam co-sputtering of segmented elemental Li and Si targets. This allows a variation of the Li fraction in LiₓSi films between 0.05 < x < 0.5 [1]. For the experiments ⁶LiₓSi/natLiₓSi isotope heterostructures were deposited and interdiffusion of ⁶Li and ⁷Li isotopes was analysed by secondary ion mass spectrometry before and after annealing. Diffusivities were extracted by comparing the experimental isotope depth profiles to analytical solutions of the diffusion equation. The diffusivities of Li₀.₁Si follow the Arrhenius law between 140 and 300 °C with an activation energy of 1.4 eV and a pre-exponential factor of 2·10⁻⁵ m²·s⁻¹. This points to a trap-limited diffusion mechanism. In contrast, for Li₀.₄Si complete isotope interdiffusion is observed directly after deposition at room temperature. These results indicate an acceleration of diffusion with increasing Li content as suggested in literature [2].

[1] Li–Si thin Films for Battery Applications Produced by Ion-beam Co-sputtering, F. Strauß, E. Hüger, P. Heitjans, V. Trouillet, M. Bruns, H. Schmidt, RSC Adv. 5 (2014) 7192.

[2] First-principles Study of the Structural and Dynamic Properties of the Liquid and Amorphous Li–Si Alloys, H.-H. Chiang, J.-M. Lu, C.-L. Kuo, J. Chem. Phys. 144 (2016) 34502.

<figure><img src="image_1.png" /></figure>