Lithium Distribution in Monocrystalline Silicon-Based Lithium-Ion Batteries

There is a growing demand on power sources for micro-system applications. Li-ion micro batteries (µ-batteries) with silicon-based anodes may fulfill the necessary requirements. Silicon shows superior properties as anode material in batteries such as a very high specific capacity [1]. Well-engineered manufacturing techniques allow a high level of integration into silicon-based semiconductor devices [2].

One challenging topic for the integration concerns lithium distribution inside the anode to understand the cyclability of silicon. Moreover, the prevention of loss of Li-ion in non-active areas of the battery is a key issue. Therefore, the introduction of a tight barrier layer is essential for such systems [3]. For these investigations analytical techniques are required, which can obtain information on the lateral as well as depth lithium distribution.

Surface structured silicon and sputtered diffusion barriers on silicon were tested as working electrodes in a half-cell Swagelok^® design together with a EC: EMC, LiPF₆-based electrolyte. Two mass spectrometry based techniques were applied to investigate the properties of structured silicon anodes together with the barrier characteristics of refectory metal materials: (i) ToF-SIMS was used as imaging technique for depth profiling the first micrometers and (ii) Laser ablation ICP-MS allowed to measure depth-profiles of up to hundreds of microns perfectly complementing the ToF-SIMS technique.

The presented study focuses on the non-uniform Li-distribution in silicon anodes with the aim to avoid structural weak hotspots due to locally unbalanced dilatation. Beside the detailed investigation of the native anode structures we tested different silicon-barrier combinations, e.g., Si – TiN, to clarify their potential as Li-inert material in future battery applications (see Fig. 1).

Acknowledgement 

Financial support by the Federal Ministry of Economy, Family and Youth and the National Foundation for Research, Technology and Development is gratefully acknowledged. Moreover, we thank Infineon Technology Austria AG for financial and technical support.

References

[1] B.A. Boukamp, G.C. Lesh, R.A. Huggins, All-solid lithium electrodes with mixed-conductor matrix. J. Electrochem. Society, 1981, 128, 4, 725-729

[2] J.F.M Oudenhoven, L. Baggetto, P.H.L Notten, All-solid state lithium-ion microbatteries: A review of various 3D concepts. Adv. Energy Mater., 2011,1, 10-33

[3] J.E. Trevey, J. Wang, C.M. Deluca, K.K. Maute, M.L. Dunn, S-H Lee, V.M. Bright, Nanostructured electrodes for solid-state 3D rechargeable lithium batteries, Sensors and Actors A167, 2011, 139-145

Figure 1: ToF-SIMS profile of a sputtered titanium nitride barrier layer on a highly doped Si substrate after 10 cycles vs. a lithium counter electrode in EC:EMC (3:7), 1 M LiPF₆.