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Issue 8, 2018
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Crystalline core/amorphous shell structured silicon nanowires offer size and structure dependent reversible Na-storage

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Abstract

One of the major bottlenecks towards the development of the Na-ion battery system is that graphitic carbon (the commonly used anode material for the Li-ion system) is not suitable for use in Na-ion system. Accordingly, in the pursuit to identify and develop a suitable anode material for the upcoming Na-ion battery system, we report here the feasibility of reversible electrochemical Na-alloying in core/shell-structured Si nanowires having crystalline (c-Si) core and amorphous (a-Si) shell. Vapor–liquid–solid mechanism during nanowire growth allowed systematic variations of the a-Si shell thickness around the c-Si core of constant diameter (∼25 nm; as per the size of Sn catalyst-cum-‘nano-template’ particles). This allowed the development of four different sets of nanowires having overall diameters varying between ∼40 (SiNW-40) and ∼460 nm (SiNW-460); thus providing platforms also for investigating the influences of the dimensional scale and structure of Si (viz., amorphous vs. crystalline) towards Na-storage. While negligible reversible Na-capacity could be recorded with the thickest nanowire set, significantly greater Na-capacities could be recorded upon reduction in the overall diameter; leading to a reversible Na-capacity of ∼390 mA h g−1 for the thinnest nanowire set (i.e., SiNW-40), which is also the highest reported to-date for ‘stand-alone’ Si-based electrodes. Shortened Na-transport distance through the a-Si shell and increased influence of the more conductive c-Si core towards the lowering of charge transfer resistance, with reduced nanowire thickness, are the causes for such a remarkable dimensional effect. Experimental evidences and analytical computational studies indicate that Na-capacity gets contributed primarily by the ‘bulk’ of the amorphous Si shell, but (interestingly) not by the crystalline Si core.

Graphical abstract: Crystalline core/amorphous shell structured silicon nanowires offer size and structure dependent reversible Na-storage

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Publication details

The article was received on 21 Nov 2017, accepted on 16 Jan 2018 and first published on 16 Jan 2018


Article type: Paper
DOI: 10.1039/C7TA10249F
Citation: J. Mater. Chem. A, 2018,6, 3422-3434
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    Crystalline core/amorphous shell structured silicon nanowires offer size and structure dependent reversible Na-storage

    M. K. Jangid, A. S. Lakhnot, A. Vemulapally, F. J. Sonia, S. Sinha, R. O. Dusane and A. Mukhopadhyay, J. Mater. Chem. A, 2018, 6, 3422
    DOI: 10.1039/C7TA10249F

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