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arXiv · 2507.16561

Microstructure of Silicon Anodes in Solid-State Batteries -- From Crystalline to Amorphous

Shamail Ahmed·Federico Rossi·Hanyu Huo·Johannes Haust·Franziska Hueppe·Juergen Belz·Andreas Beyer·Juergen Janek·Kerstin Volz
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Abstract

Silicon offers great promise as a potential anode active material and the optimum alternative to lithium metal in all-solid-state lithium-ion batteries. However, its practical application is limited by severe volume expansion (~300%) during lithiation, leading to cracking upon delithiation. In this study, we investigated the microstructural evolution of microcrystalline silicon electrodes in a solid-electrolyte-free environment using cryogenic scanning transmission electron microscopy (STEM) during electrochemical cycling. A controlled workflow prevents ambient exposure, and cryo-TEM ensures structural integrity. After the first lithiation, the electrode shows a heterogeneous mix of crystalline Li15Si4, various amorphous LixSi phases, and residual crystalline silicon. After delithiation, the structure becomes predominantly amorphous with thread-like features and minimal remaining crystallinity. By the 10th delithiation, the microstructure is more uniform, with thread-like regions mainly at grain boundaries. Our results reveal that starting from a crystalline phase, a stationary microstructure emerges in bulk silicon only after several cycles. Thus, to have a more controlled behavior of the electrode and minimize cracking, the starting material should be carefully chosen along with an optimized electrode architecture to help stabilize the microstructure throughout cycling.

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Shamail Ahmed, Federico Rossi, Hanyu Huo, Johannes Haust, Franziska Hueppe, Juergen Belz, Andreas Beyer, Juergen Janek, Kerstin Volz. 2025-07-22. Microstructure of Silicon Anodes in Solid-State Batteries -- From Crystalline to Amorphous. https://arxiv.org/abs/2507.16561

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