Combining SANS and VSANS to Extend Q -Range for Morphology Investigation of Silicon-Graphite Anodes
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ombining SANS and VSANS to Extend Q-Range for Morphology Investigation of Silicon-Graphite Anodes N. Paula, *, H. Frielinghausb, S. Buschc, V. Pipichb, and R. Gillesa aHeinz
bJülich
Maier-Leibnitz Zentrum, Technische Universität München, Garching, 85748 Germany Centre for Neutron Science at Heinz Maier-Leibnitz Zentrum, Forschungszentrum Jülich, Garching, 85748 Germany c German Engineering Materials Science Centre at Heinz Maier-Leibnitz Zentrum, Helmholtz-Zentrum Geesthacht, Garching, 85748 Germany *e-mail: [email protected] Received July 7, 2019; revised July 27, 2019; accepted August 10, 2019
Abstract—Silicon-based electrodes are attractive candidates as anodes for Li-ion batteries due to their high theoretical specific capacity. However, repeated lithiation/delithiation causes significant morphological changes in the silicon particles, which results in formation of highly porous silicon structures and severe side reactions at the silicon–electrolyte interface. To quantify such morphological changes on both the micrometer and nanometer scales, we combine the techniques of very small-angle neutron scattering (VSANS) and small-angle neutron scattering (SANS). While conventional and contrast-matched SANS data provide insight into the solid–electrolyte-interphase coverage around silicon particles and the filling of evolving porosity within the electrode, VSANS data provide information on the micrometer-sized graphite particles. Keywords: Li-ion batteries, VSANS, SANS, Si-based anodes, solid–electrolyte-interphase, pores, contrast variation DOI: 10.1134/S1027451020070368
INTRODUCTION Li-ion based rechargeable batteries with high specific energy are crucial for a wide variety of applications in consumer electronics and electromobility [1, 2], and silicon-based materials are attractive as anodes in batteries due to almost an order of magnitude higher theoretical silicon capacity (3580 mA h g–1 for Li15Si4) compared to the conventionally used graphite anode (372 mA h g–1 for LiC6) [3]. However, the major drawback of these electrodes is the expansion and contraction of silicon upon alloying and dealloying with Li, respectively. This not only results in capacity fading, but also in transformation of initially compact silicon particles into expanded porous silicon particles. Initial charge/discharge cycles result in the formation of a solid–electrolyte interphase (SEI) at the silicon–electrolyte interfaces. Wetjen et al. [4] performed a detailed study of the electrochemistry and morphology of silicon-graphite (SiG) composite anodes and showed with help of scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) that fluorine- and oxygen-containing SEI products cover fragmented Si nanostructures. With the STEM–EDS technique, it was impossible to verify whether these elements covered only the particle edges or also filled the pores. Using protonated and deuterated electrolytes, Paul et al. [5] evalu-
ated the average pore size and pore size distribution in such porous Si nanop
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