研究目的
Investigating the formation of incipient solid electrolyte interphase (SEI) layers on single crystalline silicon electrodes using scanning electrochemical microscopy to understand their passivating properties and local initiation during charging.
研究成果
SECM imaging revealed that incipient SEI formation on single crystalline silicon electrodes occurs through local nucleation and lateral growth, starting at around 1.0 V vs. Li/Li+. This heterogeneous growth happens even on atomically smooth surfaces, providing new insights into SEI formation mechanisms. The findings suggest opportunities for optimizing SEI formation protocols in lithium-ion batteries.
研究不足
The study avoids lithiation to prevent morphological changes, which may not fully represent real battery cycling conditions. The resolution of SECM is limited to micrometers, potentially missing smaller SEI precursor regions. Experiments were conducted in a specific electrolyte (propylene carbonate with LiClO4 and DBDMB), which may not generalize to other electrolytes.
1：Experimental Design and Method Selection:
The study used scanning electrochemical microscopy (SECM) to image SEI formation in situ. A redox mediator (DBDMB) was employed for feedback mode imaging. Potentiodynamic charging via linear sweep voltammetry (LSV) was conducted to form SEI layers without lithiation to avoid morphological changes.
2：Sample Selection and Data Sources:
Monocrystalline silicon wafers (200 μm thickness, <100> orientation, resistivity 8 mΩ cm) were used as electrodes. A Cu layer was sputtered as a current collector, and the native oxide layer was removed with HF acid.
3：List of Experimental Equipment and Materials:
Equipment included a potentiostat (CompactStat, Ivium Technologies), a 3-axis micropositioning system (MS30, PS30, CU30, mechOnics AG), Pt microelectrodes (25 μm diameter, Goodfellow GmbH), borosilicate glass capillaries (Hilgenberg GmbH), and an Ar-filled glove box (Uni-Lab, M. Braun GmbH). Materials included 2,5-di-tert-butyl-1,4-dimethoxybenzene (DBDMB), LiClO4, propylene carbonate (G27, BASF), and hydrofluoric acid.
4：Experimental Procedures and Operational Workflow:
Silicon samples were prepared by removing native oxide with HF, rinsed, dried, and transferred to a glove box. SECM imaging was performed with the microelectrode polarized to +4.1 V vs. Li/Li+. The electrode was approached until current doubled, then scanned. Charging was done via LSV from 1.4 V to 0.5 V vs. Li/Li+ at 20 μV s-1. After each charging step, SECM images were taken of the same region after a 15-minute delay.
5：1 V vs. Li/Li+. The electrode was approached until current doubled, then scanned. Charging was done via LSV from 4 V to 5 V vs. Li/Li+ at 20 μV s-After each charging step, SECM images were taken of the same region after a 15-minute delay.
Data Analysis Methods:
5. Data Analysis Methods: SECM images were analyzed for current variations to assess passivation. Histograms of microelectrode currents were constructed to track SEI development. Data interpretation focused on nucleation and growth patterns of SEI layers.
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