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3D Visualization of Inhomogeneous Multi-Layered Structure and Young’s Modulus of SEI on Silicon Anode for Lithium-Ion Batteries
Jieyun Zheng, Hao Zheng, Fei Luo, Wenjun Li and Hong Li*
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, China
Correspond to hli@iphy.ac.cn
Introduction
Solid Electrolyte interphase (SEI) grown on electrode surface in non-aqueous lithium batteries was firstly purposed by Peled in 1979.1 Grate efforts have been paid since then to explore the chemical composition, structure and formation mechanism of SEI during cycling. Many techniques such as X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), transmission electronic microscopy (TEM), second ion mass spectroscopy (SIMS), electrochemical impedance spectroscopy (EIS), mass spectroscopy (MS) and thermo gravimetric-differential scanning calorie (TG-DSC) have been used to get a complete picture of SEI. It is generally accepted that the SEI is layer-structured with inorganic part such as Li2CO3, Li2O, LiF covers the electrode first and followed by the organic part such as LiCH3, LiOCO2CH3 and LiOCH3 covers the first layer. However, profound understanding of micro-structure of the SEI still remains a challenge. A particular example is silicon which is a promising high capacity anode for the next generation lithium batteries but it suffers from large volume variation and continuous formation/destruction of unstable SEI film. Herein, an atomic force microscopy (AFM) based method2 is developed which can directly and three-dimensionally (3D) visualize the multi-layered structure and mechanical properties of the SEI formed on silicon anode materials. We, thus, propose a novel mechanism of the dynamic process of the SEI formation on the silicon anode accordingly.
Based on force curve method, a cross-section 3D image of the SEI film on silicon thin film anode can be provided. Single-layered, double-layered, and multi-layered structures with various Young’s Modulus and thickness coexist at different sites on the surface of silicon. The SEI layers with higher Young’s modulus have higher probability to appear at the bottom layer. The total coverage without additive in the electrolyte of the SEI is only about 50% even when the electrode in a half cell was discharged to 0.005 V vs Li+/Li and kept potentialstatistically for 48 hours.
Our recent investigations on formation process, electrochemical stability, layered structure and coverage, mechanical properties, influences of temperatures, additives, impurity on the SEI, will be introduced in this meeting.
Acknowledge:
Financial support from CAS project (KJCX2-YW-W26), "Strategic Priority Research Program" of the Chinese Academy of Sciences，Grant No. XDA09010102 and National project 973 (2012CB932900) are appreciated.
Reference:
[1] E. Peled, J. Electrochem. Soc. 1979, 126, 2047
[2] J. Zhang, R. Wang, X. Yang, W. Lu, X. Wu, X. Wang, H. Li, L. Chen, Nano letters 2012, 12, 2153