Leveraging Titanium to Enable Silicon Anodes in Lithium‐Ion Batteries

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2018-10, Vol.14 (41), p.e1802051-n/a
• Main Authors: Lee, Pui‐Kit, Tahmasebi, Mohammad H., Ran, Sijia, Boles, Steven T., Yu, Denis Y. W.
• Format: Article
• Language: English
• Subjects: anode material; Anodes; Cycles; Dilatometry; Disintegration; Electrode materials; full cell demonstration; Gravimetry; high cycling stability; Lithium-ion batteries; lithium‐ion battery; Nanotechnology; Raman spectroscopy; Silicon; Silicon films; Si–Ti thin film; Thickness; Thin films; Titanium
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.201802051

Silicon is a promising anode material for lithium‐ion batteries because of its high gravimetric/volumetric capacities and low lithiation/delithiation voltages. However, it suffers from poor cycling stability due to drastic volume expansion (>300%) when it alloys with lithium, leading to structural disintegration upon lithium removal. Here, it is demonstrated that titanium atoms inside the silicon matrix can act as an atomic binding agent to hold the silicon atoms together during lithiation and mend the structure after delithiation. Direct evidence from in situ dilatometry of cosputtered silicon–titanium thin films reveals significantly smaller electrode thickness change during lithiation, compared to a pure silicon thin film. In addition, the thickness change is fully reversible with lithium extraction, and ex situ post‐mortem microscopy shows that film cracking is suppressed. Furthermore, Raman spectroscopy measurements indicate that the Si–Ti interaction remains intact after cycling. Optimized Si–Ti thin films can deliver a stable capacity of 1000 mAh g−1 at a current of 2000 mA g−1 for more than 300 cycles, demonstrating the effectiveness of titanium in stabilizing the material structure. A full cell with a Si–Ti anode and LiFePO4 cathode is demonstrated, which further validates the readiness of the technology. Incorporation of titanium atoms into a silicon matrix significantly enhances the cycling performance of the thin film anode for lithium‐ion batteries. The optimal Si–Ti thin film electrode exhibits high gravimetric and volumetric capacities as well as excellent long‐term cycling stability even in a full‐cell configuration with LiFePO4.