Investigation of grafted mesoporous silicon sponge using hyperpolarized 129 Xe NMR spectroscopy
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ARTICLE Investigation of grafted mesoporous silicon sponge using hyperpolarized 129Xe NMR spectroscopy Yougang Mao Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
Dokyoung Kima) Department of Anatomy and Neurobiology, Kyung Hee University, Seoul 02447, Republic of Korea; and Center for Converging Humanities, Kyung Hee University, Seoul 02447, Republic of Korea
Russell Hopson Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA
Michael J. Sailor Department of Chemistry and Biochemistry, University of California, San Diego, California 92093, USA
Li-Qiong Wangb) Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA (Received 3 March 2018; accepted 14 June 2018)
Temperature-dependent (173–373 K) hyperpolarized 129Xe nuclear magnetic resonance (129Xe NMR) analyses along with transmission electron microscopy and N2 adsorption measurements have been applied to understand pore structure and interconnectivity of bare and grafted mesoporous silicon sponge (MSS) materials. The Xe NMR chemical shift data indicate the existence of micropores inside the larger mesopore channels and the effects of grafting on the pore surfaces. The grafted layer estimated at 2 nm in thickness blocks the micropores on the surfaces of mesoporous channels. Partitioning of Xe between the micropores and the mesopores in the MSS materials is temperature-dependent, with Xe principally occupying the micropores at lower temperatures. In addition, the temperature-dependent Xe peak shift of MSS materials verifies the increased uniformity and interconnectivity of mesopores after surface grafting. The results from this study provide useful information for design and development of novel materials.
I. INTRODUCTION
Energy storage devices such as lithium-ion batteries (LiBs) are important for portable devices, electrical vehicles, and power tools.1,2 The increasing demand has led researchers to focus on improving energy density, durability, cycling ability, charging time, and low-cost LiBs.3–8 So far, various kinds of positive and negative electrodes have been developed, and readily available cost-efficient silicon materials have come into the spotlight.7,8 Silicon is electrically conductive and can swell modestly to accommodate the lithium ions, exhibiting superior properties as a LiB anode.9 However, the large volume expansion (.300%) during the lithiation process leads to the pulverization of silicon materials along with considerable microstructural degradation, resulting in the disruption of electron-conducting paths, and loss of reversible capacity.10–13
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2018.226 J. Mater. Res., Vol. 33, No. 17, Sep 14, 2018
Mesoporous silicon sponge (MSS) with its preformed meso/macropore structures and the grafted carbon on the surface has been demonstrated as a robust anode material to accommodate the large volume expansion that accompanies the lithiation process
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