Elsevier

Electrochimica Acta

Volume 55, Issue 12, 30 April 2010, Pages 3909-3914
Electrochimica Acta

Large reversible capacity of high quality graphene sheets as an anode material for lithium-ion batteries

https://doi.org/10.1016/j.electacta.2010.02.025Get rights and content

Abstract

High quality graphene sheets were prepared from graphite powder through oxidation followed by rapid thermal expansion in nitrogen atmosphere. The preparation process was systematically investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and Brunauer–Emmett–Teller (BET) measurements. The morphology and structure of graphene sheets were characterized by scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM). The electrochemical performances were evaluated in coin-type cells versus metallic lithium. It is found that the graphene sheets possess a curled morphology consisting of a thin wrinkled paper-like structure, fewer layers (∼4 layers) and large specific surface area (492.5 m2 g−1). The first reversible specific capacity of the prepared graphene sheets was as high as 1264 mA h g−1 at a current density of 100 mA g−1. Even at a high current density of 500 mA g−1, the reversible specific capacity remained at 718 mA h g−1. After 40 cycles, the reversible capacity was still kept at 848 mA h g−1 at the current density of 100 mA g−1. These results indicate that the prepared high quality graphene sheets possess excellent electrochemical performances for lithium storage.

Introduction

Lithium-ion batteries have been widely used in portable electronic devices and regarded as promising devices in the application of electric vehicles. The energy density and performance of lithium-ion batteries largely depend on the physical and chemical properties of cathode and anode materials. Graphite is the widely commercial anode material for lithium-ion batteries because of its high columbic efficiency and better cycle performance. However, the theoretical specific capacity of graphite is only 372 mA h g−1 (by forming intercalation compounds (LiC6)) [1]. Because of the capacity limit of graphite, the energy density of lithium-ion battery cannot satisfy the requirement of portable electronic devices and recently developed full electric vehicles. To meet the increasing demand for batteries with high energy density, much effort has been made to explore new anode materials [2], [3], [4], [5], [6].

Graphene is the name given to a two-dimensional sheet of sp2-hybridized carbon. Its extended honeycomb network is the basic building block of other important allotropes: it can be stacked to form 3D graphite, rolled to form 1D nanotubes, and wrapped to form 0D fullerenes [7]. So far, 1D nanotubles and 0D fullerenes have been used as anode materials in lithium-ion batteries and exhibit improved electrochemical performances [8], [9], [10], [11], [12], [13], [14]. But these carbon materials only show a limited enhancement of the performance compared with 3D graphite. Freestanding graphene was experimentally discovered by Novoselov and Geim in 2004 [15], but its chemical and physical understanding is still in the primary stage [16]. Recently, graphene nanosheets as anode materials were investigated and exhibited large reversible capacity [14], [17], [18], [19], but the graphene nanosheets used in lithium-ion batteries consists of more layers. It is well known that the performance of nanomaterials largely depends on their structures and morphologies, therefore, the graphene sheets with fewer layers maybe have better electrochemical performances. Indeed, it has been demonstrated that the graphene sheets of ca. 0.7 nm thickness could provide the highest storage density (with a Li4C6 stoichiometry) by density of states calculations [20]. Single graphene sheets derived from splitting graphite oxide have been successfully prepared by Schniepp through thermal exfoliation in 2006 [21]. However, to our best knowledge, the electrochemical performances of the graphene sheets with fewer layers have never been reported. In this study, high quality graphene sheets with fewer layers (∼4 layers) and large specific surface area (492.5 m2 g−1) were successfully prepared through thermal exfoliation. The electrochemical performances for the lithium storage were evaluated in coin-type cells.

Section snippets

Synthesis of graphene sheets

Graphene sheets were prepared in two steps: graphite powder (Shanghai Colloid Chemical Plant, China) was oxidized to graphite oxide via a modified Hummers’ method [22], and then rapidly exfoliated at high temperatures under nitrogen atmosphere to obtain graphene sheets. In a typical reaction, 2 g graphite powder with the average particle size 30 μm, 2 g sodium nitrate (AR, Tianjin Fu Chen Chemical Reagent Factory, China) and 100 mL of concentrated sulfuric acid (AR, Beijing Chemical Plant, China)

Results and discussion

XRD patterns of graphite powder, graphite oxide and graphene sheets are presented in Fig. 1. The XRD pattern of graphite powder exhibits a characteristic peak (0 0 2) of graphite at 26.58°. After oxidation, the (0 0 2) peak of graphite powder disappears and an additional peak at 11.36° is observed, which is corresponding to the (0 0 1) diffraction peak of graphite oxide. The d-spacing of graphite oxide increased to 0.779 nm from 0.335 nm of graphite powder, which is ascribed to the oxide-induced

Conclusions

The high quality graphene sheets with a curled morphology consisting of a thin wrinkled paper-like structure, fewer layers (∼4 layers) and a large specific surface area (492.5 m2 g−1) were prepared using a thermal exfoliation method. The electrochemical performance testing showed that the first reversible specific capacity of the prepared graphene sheets was as high as 1264 mA h g−1 at a current density of 100 mA g−1. After 40 cycles at different current densities of 100 mA g−1, 300 mA g−1, 500 mA g−1 and

Acknowledgements

This work was supported by Program for New Century Excellent Talents in Chinese Ministry of Education (no. NECT-07-0307) and by the Natural Science Foundation of China (no. 20936001).

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