Synthesis of graphene nanosheets by the electrolytic exfoliation of graphite and their direct assembly for lithium ion battery anodes

https://doi.org/10.1016/j.matchemphys.2012.04.043Get rights and content

Abstract

Graphene nanosheets were produced through electrolytic exfoliation of graphite foils in an aqueous solution containing an electrolyte, poly(sodium-4-styrenesulfonate). We confirmed the formation of graphene nanosheets by X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy. The electrochemical performance of the graphene nanosheets was evaluated using cyclic voltammetry, galvanostatic charge–discharge cycling, and electrochemical impedance spectroscopy. In order to address the feasibility of their use as lightweight anodes for a Li ion battery, we also present the direct assembly of graphene nanosheets onto metal current collectors and the fabrication of freestanding graphene nanosheets paper electrodes.

Highlights

► Graphene nanosheets were electrolytically synthesized from graphite foils. ► The direct electrophoretic deposition of the graphenes onto current collectors is described. ► Promising Li storage capabilities of graphene anode were found.

Introduction

In a conventional lithium ion battery (LIB), graphite and graphitized carbonaceous materials have been used primarily as anodes because these graphite-based anodes show a highly negative potential and good cyclability with safety. For the purpose of enhancing LIB electrochemical performance, there are several ongoing efforts to develop advanced anodes using surface modification, chemical doping, and other types of heat-treated carbons [1], [2], [3], [4], [5].

Recently, one emerging and extraordinary carbon nanostructure, graphene, was discovered, possessing fascinating properties that include atomic thickness/high surface area, high mobility of charge carriers, high mechanical strength, chemical and thermal tolerance, and nontoxicity [6], [7]. The graphene is a two-dimensional (2D) form with single to few layers. It has attracted attention for applications in the fundamentals of the science and industrial technology, like nanoelectronics, composites, molecular gas sensors, and field-emission devices [8], [9], [10], [11]. Furthermore, graphene exists as a freestanding form and has ballistic movement behavior of electrons due to the high quality of the sp2 carbon lattice [12]. Therefore, there is considerable room for graphene as a good electrode for a high-performance lithium ion battery. Indeed, large reversible capacities have been reported in graphene electrodes due to the large interlayer spacing and significant disorder/defects, enabling the accommodation of additional Li [13], [14].

In order to produce a graphene, simple and effective methods were investigated using micromechanical cleavage, graphite intercalation, reduction of graphite oxide, and growth on SiC wafers or metal substrates [15], [16], [17], [18], [19]. The micromechanical cleavage from graphite, repeating a peel-off process, is the most experimental studied among others, because this process can provide pristine graphene layers without additional surface contamination or chemical modification. However, there is a disability towards controlling the shape and size, with a limitation towards producing a quantity of graphene. Thus, achieving scaled-up production of graphene is the most important and challenging obstacle; research has subsequently focused on highly efficient synthesis of graphene. Imidazolium-based ionic liquid-assisted electrochemical exfoliation has recently been reported as a simple means to generate graphene from graphite electrode [20], [21]. Notably, Wang et al. first reported the preparation of graphene from a high-purity graphite rod by electrolytic exfoliation in an aqueous electrolyte solution containing poly(sodium-4-styrenesulfonate) (PSS) [22]. The present authors also observed the surface modification of as-received flexible graphite foils based on the formation of graphene under the aid of an aqueous electrolyte containing PSS [23].

Herein, we attempted to produce large quantities of freestanding graphene nanosheets (GNSs) from graphite foils by electrolytic exfoliation in the same medium containing PSS. The microstructural and electrochemical properties of these GNSs were carefully investigated. The direct electrophoretic deposition of the GNSs onto metal current collectors was also described, without the need for polymer binders or conductive additives. Furthermore, GNSs was successfully assembled into current collector-free paper electrodes using the vacuum filtration process, which would be applicable to lightweight LIBs. Fig. 1 illustrates a conceptual representation of the aforementioned fabrication processes for GNSs-based electrodes in this study.

Section snippets

Synthesis of GNSs

The starting material for the stationary anode was a flexible graphite sheet, Grafoil® (0.25 mm thick, GrafTech). A copper foil (25 μm thick, Aldrich) supported by a glass plate, was used as the counter electrode with a separation of 2 cm. For synthesis of the GNSs by electrolytic exfoliation, 0.001 M of an aqueous electrolyte containing PSS (molecular weight = 70,000, Aldrich) was used, similar to a previously reported electrochemical synthetic process of GNSs [22]. The constant current

Results and discussion

The starting graphite foil consists of pressed flakes having a smooth surface as shown in Fig. 2a. After the electrolytic process in the suspension containing PSS, visible expansion of graphite foil was observed. The expanded sheets peeled off from the graphite foil and formed a homogeneous dark suspension without sedimentation after washing (Fig. 2b). Fig. 2c shows the field-emission scanning electron microscopy (FESEM) image of the dried particles after centrifugation of the suspension,

Conclusions

We have prepared GNSs using the simple, fast, and green electrolytic exfoliation of graphite foil with the assistance of an aqueous solution containing PSS. The intrinsic properties of the GNSs, such as 1–10 layer stacking of the monatomic graphene sheets, high surface area, and presence of a considerable amount of defects, allowed enhanced electrochemical performance compared to as-received graphite foil. A large-area electrode of the colloidal GNSs suspension was also produced without

Acknowledgements

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No. 2011-0019119, 2011-0030745, and 2011-0030300).

References (40)

  • Y.P. Wu et al.

    J. Power Sources

    (2002)
  • J.R. Dahn et al.

    Electrochim. Acta

    (1993)
  • J. Wu et al.

    Chem. Rev.

    (2007)
  • I. Lahiri et al.

    Carbon

    (2011)
  • S. Stankovich et al.

    Carbon

    (2007)
  • J. Wintterlin et al.

    Surf. Sci.

    (2009)
  • G. Wang et al.

    Carbon

    (2009)
  • S.H. Lee et al.

    Electrochem. Commun.

    (2010)
  • Z.Q. Li et al.

    Carbon

    (2007)
  • E. Frackowiak et al.

    Carbon

    (1999)
  • H. Kim et al.

    Nano Res.

    (2010)
  • C. Wang et al.

    Electrochim. Acta

    (2001)
  • A.R. Boccaccini et al.

    Carbon

    (2006)
  • J.W. Choi et al.

    J. Power Sources

    (2010)
  • A.L.M. Reddy et al.

    ACS Nano

    (2010)
  • W.J. Weydanz et al.

    J. Electrochem. Soc.

    (1994)
  • R. Fong et al.

    J. Electrochem. Soc.

    (1990)
  • A.K. Geim et al.

    Nature

    (2007)
  • L.A. Ponomarenko et al.

    Science

    (2008)
  • S. Watcharotone et al.

    Nano Lett.

    (2007)
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