Elsevier

Solid State Ionics

Volume 258, 1 May 2014, Pages 67-73
Solid State Ionics

Coaxial electrospun Si/C–C core–shell composite nanofibers as binder-free anodes for lithium-ion batteries

https://doi.org/10.1016/j.ssi.2014.02.003Get rights and content

Highlights

  • Si/C-C core-shell nanofibers were designed by dual nozzle coaxial electrospinning.

  • Carbon shell buffers volume change and restrains capacity fading of the Si/C core.

  • Si/C-C core-shell nanofibers show high discharge capacity after prolonged cycling.

Abstract

Si/C–C core–shell nanofiber structure was designed by dual nozzle coaxial electrospinning and subsequent carbonization. This core–shell nanofiber structure has Si/C composite as the core and carbon as the shell. Used as an anode in lithium-ion batteries, the carbon shell can help buffer the large volume expansion/contraction of the Si/C core during charge/discharge and restrain the capacity fading caused by the mechanical failure of the active material. Results showed that after 50 cycles, the discharge capacity of Si/C–C core–shell composite nanofibers was 63% higher than that of Si/C composite nanofibers and the capacity retention increased from 48.6 to 72.4%. It is, therefore, demonstrated that Si/C–C core–shell composite nanofibers are promising anode material with large reversible capacity and good cycling stability.

Introduction

Lithium-ion batteries (LIBs) have the advantages of high energy density, broad operating temperature range, low self-discharge rate, long cycle life, high voltage, and no voltage depression [1], [2]. High-performance LIBs as the key electrical energy storage device are now in high demand for electric vehicles, plug-in hybrid electric vehicles, and grid storage systems. However, commercially-used graphite anode material only has a theoretical capacity of 372 mAh g 1, which is not sufficient to meet the high energy-storage demands [3], [4]. Hence alternative anode materials with higher capacities are urgently needed to increase the energy density and performance of lithium-ion batteries.

Si is a promising anode material for next-generation LIBs due to its extremely large capacity of 3579 mAh g 1 (Li15Si4 phase), which is about ten times greater than that of the commercially-used graphite anode [5], [6]. However, during repeated lithium insertion/extraction processes, the accompanied huge volume change induces the structural failure of the active material and accelerates the formation of new solid electrolyte interphase (SEI), resulting in rapid capacity fading and poor cycling life. To overcome this problem, many approaches have been suggested, including using Si-based thin films [7], [8], Si nanowires [9], [10], [11], Si nanotubes [12], [13], dispersing Si into inactive/active matrix [14], [15], [16], [17], [18], etc. Among all approaches, electrospinning is a simple, low-cost and scalable method of forming continuous Si-containing nanofibers [19], [20], [21], [22]. These nanofibers could form free-standing, conductive and three-dimensional interconnected webs, which possess good elasticity to maintain the structure integrity and stable electrically-conductive networks. When used as anodes for rechargeable LIBs, three-dimensional interconnected nanofiber webs can provide continuous pathways for efficient charge transport along the fiber axis and excellent structural buffering effect to absorb the mechanical stress upon lithium insertion/extraction.

In this work, we designed a Si/C–C core–shell nanofiber structure to improve the cycling performance of Si-based anodes by dual nozzle coaxial electrospinning of Si/PAN and PAN precursor solutions, with Si/PAN as the core and PAN as the shell, followed by carbonization. Fig. 1 shows a schematic of the dual nozzle coaxial electrospinning setup. The resultant core–shell nanofiber structure has Si/C composite as the core and carbon as the shell. The carbon shell can help buffer the large volume expansion/contraction of the Si/C core during charge/discharge and restrain the capacity fading caused by the mechanical failure of the active material. The resultant Si/C–C core–shell composite nanofibers form free-standing conductive membranes that can be used directly as battery electrodes without adding carbon black conductor or polymer binder. Results indicate that the Si/C–C core–shell nanofiber structure can significantly improve the electrochemical performance of Si-based anodes for high-energy LIBs. Since the fabrication process is low cost, facile, and scalable, the core–shell nanofiber structure demonstrated in this work could also be helpful for other energy storage applications.

Section snippets

Electrode preparation

Si nanoparticles (diameter: 30–50 nm) were purchased from Nanostructured & Amorphous Materials, Inc. Polyacrylonitrile (PAN, 150,000 g mol 1) was purchased from Pfaltz & Bauer Inc. N,N-dimethylformamide (DMF) was purchased from Aldrich. All these reagents were used without further purification. The inner core dispersion for electrospinning was prepared by adding 20 wt.% Si nanoparticles into an 8 wt.% PAN solution in DMF. The outer shell solution for electrospinning was 8 wt.% PAN in DMF. Both the

Morphology and structure

Fig. 2 shows the digital photographs of the dispersion/solution droplet at the nozzle tip during the dual nozzle electrospinning process. Before applying the high voltage (20 kV), the dispersion/solution droplet clearly shows a core–shell structure with Si/PAN dispersion as the core, encapsulated by the PAN solution. After applying a voltage of 20 kV, the liquid droplet becomes highly electrified and a Taylor cone is formed at the nozzle tip. A charged jet of the liquid dispersion/solution is

Conclusions

In this work, a Si/C–C core–shell nanofiber structure was prepared to improve the cycling performance of Si-based anodes by dual nozzle coaxial electrospinning and subsequent carbonization. This core–shell nanofiber structure has Si/C composite as the core and carbon as the shell. The carbon shell can help buffer the large volume expansion/contraction of the Si/C core during charge/discharge and restrain the capacity fading caused by the mechanical failure of the active material. The specific

Acknowledgments

This research was supported by the U.S. Department of Energy under Grant No: DE-EE0001177, Advanced Transportation Energy Center, and ERC Program of the National Science Foundation under Award Number EEC-08212121.

References (26)

  • E. Buiel et al.

    Electrochim. Acta

    (1999)
  • D. Aurbach et al.

    Solid State Ionics

    (2002)
  • Y. Li et al.

    Carbon

    (2013)
  • L. Ji et al.

    Electrochim. Acta

    (2010)
  • Z. Lin et al.

    J. Power Sources

    (2010)
  • M. Armand et al.

    Nature

    (2008)
  • B. Dunn et al.

    Science

    (2011)
  • M.N. Obrovac et al.

    Electrochem. Solid-State Lett.

    (2004)
  • M.N. Obrovac et al.

    J. Electrochem. Soc.

    (2007)
  • P.R. Abel et al.

    ACS Nano

    (2012)
  • M.D. Fleischauer et al.

    J. Electrochem. Soc.

    (2008)
  • C.K. Chan et al.

    Nat. Nanotechnol.

    (2007)
  • C.K. Chan et al.

    ACS Nano

    (2010)
  • Cited by (37)

    • High safety and electrochemical performance electrospun para-aramid nanofiber composite separator for lithium-ion battery

      2022, Composites Science and Technology
      Citation Excerpt :

      A LIB is mainly composed of electrode, electrolyte and a separator. So far, much attention has been devoted to improving the energy and power density of the anode and cathode of LIBs, such as the use of nanostructured materials and thin polymer membranes [9–12]. Although many issues regarding the performance and stability of electrodes are still unresolved, more attention should be paid to the separator, because the separator plays an equally important role in the performance and safety of the battery.

    • The pitch-based silicon-carbon composites fabricated by electrospraying technique as the anode material of lithium ion battery

      2020, Journal of Alloys and Compounds
      Citation Excerpt :

      The examples include core-shell [11], porous [12] and yolk-shell [13] structures. Core-shell structure is capable of absorbing the mechanical stress and maintain the structural integrity [14]. Pores in the material give the space to accommodate the mechanical strain [6].

    • Toward understanding the interaction within Silicon-based anodes for stable lithium storage

      2020, Chemical Engineering Journal
      Citation Excerpt :

      After few dozens of charging cycles of CNFs based Si anode, new sites in broken structure become as host platform for unstable SEI film formation. To overcome these shortcomings from Si-embedded CNFs network for anode, several structural modifications have been made such as Si hollow CNFs, Si coated CNFs, core shell Si-CNFs and 3D composite CNFs [141–143]. Si encapsulated in hollow-CNFs with hierarchical core–shell structure was prepared by electrospinning method [144].

    • Core-shell materials for advanced batteries

      2019, Chemical Engineering Journal
    View all citing articles on Scopus
    View full text