Microsc. Microanal. 23, 1107–1115, 2017 doi:10.1017/S1431927617012739
Letter to the Editor
In Situ High-Resolution Transmission Electron Microscopy (TEM) Observation of Sn Nanoparticles on SnO2 Nanotubes Under Lithiation
Jun Young Cheong,1,a Joon Ha Chang,1,2,a Sung Joo Kim,1,2 Chanhoon Kim,1 Hyeon Kook Seo,1,2 Jae Won Shin,2 Jong Min Yuk,1,* Jeong Yong Lee,1,2,* and Il-Doo Kim1,*
1Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 335 Science Road,
Daejeon, 305-701, Republic of Korea 2Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS), Daejeon, 305-701, Republic of Korea
Abstract: Wetrace Sn nanoparticles (NPs) produced from SnO2 nanotubes (NTs) during lithiation initialized by high energy e-beam irradiation. The growth dynamics of Sn NPs is visualized in liquid electrolytes by graphene liquid cell transmission electron microscopy. The observation reveals that Sn NPs grow on the surface of SnO2 NTs via coalescence and the final shape of agglomerated NPs is governed by surface energy of the Sn NPs and the interfacial energy between Sn NPs and SnO2 NTs. Our result will likely benefit more rational material design of the ideal interface for facile ion insertion.
Key words: SnO2, agglomeration, in situ TEM, graphene liquid cell, lithium ion battery
INTRODUCTION Lithium ion batteries (LIBs) are widely used in portable electronics, electronic vehicles, and energy storage systems (Tarascon & Armand, 2001; Edström et al., 2004; Piper et al., 2015). As these devices continuously demand higher capacity and power, optimization of anode materials is essential for advanced LIBs. Among diverse candidates for the anode, nanostructured metal oxides have attracted great attention due to their high theoretical capacity, safety, and natural abundance (Peled et al., 1996; Wang et al., 2015). During lithiation, the metal oxide undergoes a conversion reaction (MOx+2xLi→M+xLi2O) followed by alloying reaction of producing metal with Li. In repetitive the lithia- tion/delithiation process, metal byproducts agglomerate to each other, leading the loss of electrical contact and eventually leading to fading of the capacity of the cell during cycling (Zhou et al., 2015). In order to prevent the agglom- eration, the dynamics should be addressed. Especially, understanding of the metal behavior during the solid electrolyte interface (SEI) layer formation is important because metal byproducts can affect compositions and morphologies of the SEI layer, which influence the performance of electrochemical cells (Zheng et al., 2014; Kim et al., 2015; Cheong et al., 2016). During the past decade, in situ transmission electron
microscopy (TEM) has been developed and employed to visualize the reaction-induced morphological and phase
Received August 29, 2017; accepted October 31, 2017
*Corresponding authors.
jongmin.yuk@kaist.ac.kr;
j.y.lee@kaist.ac.kr;
idkim@kaist.ac.kr aThese authors contributed equally to this work.
changes in electrode materials, including Si (Gu et al., 2012; McDowell et al., 2013; Kim et al., 2015), metal oxides (Huang et al., 2010; Wang et al., 2011; Kim et al., 2014), and metal sulfides (McDowell et al., 2015; Zeng et al., 2015; Gao et al., 2016). Nevertheless, significant challenges still remain when trying to observe the conversion dynamics occurring at the interface between the active material and the electrolyte during lithiation. This is mainly because of both insufficient temporal and spatial resolution to monitor atomic-scale changes at an interface which has a thickness of tens of nanometers or less. Here, we employ an in situ graphene liquid cell (GLC)
TEM allowing straughtforward sample fabrication and high- resolution imaging and monitor dynamic agglomeration behaviors of Sn nanoparticles (NPs), produced from the conversion reaction of SnO2 nanotubes (NTs) during the chemical lithiation initialized by e-beam irradiation.
MATERIALS ANDMETHODS
Synthesis of SnO2 NTs SnO2 NTs were synthesized by electrospinning and sub- sequent calcination. Sn precursor/polyvinylpyrrolidone (PVP) composite nanofibers (NFs) were first fabricated by electrospinning and SnO2 NTs were formed after calcination, due to the Kirkendall effect and Ostwald ripening, as reported in a previous study (Cheong et al., 2016). For the electrospinning solution, 0.25 g of tin chloride dehydrate (SnCl2·H2O; Sigma Aldrich, St. Louis, MO, USA) was mixed with 1.25 g of ethanol (C2H6O; Merck, Kenilworth, NJ, USA) and stirred for 2h. Then, 0.35 g of PVP
© MICROSCOPY SOCIETY OF AMERICA 2017
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