Elsevier

Applied Surface Science

Volume 509, 15 April 2020, 145352
Applied Surface Science

Full Length Article
Amorphous MoSx embedded within edges of modified graphite as fast-charging anode material for rechargeable batteries

https://doi.org/10.1016/j.apsusc.2020.145352Get rights and content

Highlights

  • We synthesized MoSx@B-rGtO using mechanical and chemical procedures.

  • The number of exposed edges was increased by the ball-milling process.

  • Oxygen species played a role in anchoring between MoSx and modified graphite.

  • Graphite-based composite exhibits fast charging property and excellent stability.

Abstract

Anode materials with high Li storage capacity and fast charging/discharging characteristics are necessary to produce high-performance lithium-ion batteries (LIBs) for future clean electric and hybrid vehicles. Several researchers have suggested that nanomaterials with excellent electrochemical performances have the potential to overcome the limitations of current LIBs. However, owing to their complex synthetic fabrication methods, low tap density, and poor first coulombic efficiency, they are not favorable as commercial anode materials. In this study, we introduce a straightforward strategy to fabricate anode materials based on commercially suitable graphite to satisfy the requirements of future LIBs. Graphite was modified by ball-milling and mild oxidation, which led to an increase in the number of exposed edges and anchoring sites between the graphite and the amorphous molybdenum sulfide (MoSx). MoSx, which is an important component of several high capacity materials, was stable under a high C-rate condition owing to its oxygen functional groups. The MoSx@B-rGtO electrode exhibited excellent specific capacity (1239 and 403 mAh g−1 at current densities of 0.13 and 2.60 A g−1, respectively) and cycling stability (1016 mAh g−1 after 100 cycles). Therefore, we believe that our graphite-based anode material can be used as a potential LIB electrode for future electric automobiles.

Graphical abstract

Amorphous MoSx was embedded within edges of modified graphite through mechanical and chemical procedures for fast-charging anode material.

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Introduction

Rechargeable lithium-ion batteries (LIBs) have been extensively used in portable electronics owing to their flexibility and lack of memory effects [1], [2], [3], [4]. Graphite has several advantages as an anode material, including a flat potential profile (0.3 V vs Li/Li+), relatively low cost, superior electrical conductivity, and structural stability during lithiation/de-lithiation [2], [5], [6], [7], [8]. However, as demands for eco-friendly vehicles have risen, several researchers have attempted to replace graphite—which has drawbacks such as a low theoretical capacity (372 mAh g−1, LiC6) and slow lithium ion diffusivity—with nanomaterials having high capacity and fast charging/discharging characteristics [9], [10], [11]. Among the alternative anode materials, molybdenum sulfide (MoSx) has been considered because its conversion reaction leads to a higher theoretical specific capacity (~670 mAh g−1) compared with commercial graphite [12], [13], [14]. Nevertheless, MoSx exhibits some disadvantages, including structural deterioration during repeated charging and discharging and semiconducting property that lead to low stability [12], [15], [16], [17].

To address these critical issues, several strategies to form composites of MoSx and nanocarbon have been proposed [18], [19], [20], [21], [22]. It is well known that nanocarbon materials provide large electrochemically active surface areas and electron transfer pathways owing to their porous structure with exposed edges and sp2 hybridization, respectively [23], [24], [25], [26], [9], [27]. In addition, nanocarbon-based electrodes exhibit good contact with the electrolyte and a short pathway for both electron and Li-ion transports, leading to fast charging/discharging rates [28], [29]. Li et al. reported that MoS2 directly grown on the surface of carbon nanotubes (CNTs) showed excellent electrochemical performance owing to the strong interaction between the semiconducting MoS2 and the conductive CNTs [30]. Similarly, Shi et al. synthesized hierarchical MoSx/CNT nanocomposites via a solvent thermal method. This hierarchical structure maximized the surface area and increased the interlayer spacing, resulting in a lower strain and a smaller intercalation barrier of Li ions, which yielded a large lithium storage capability, stable cycling performance, and excellent charge/discharge rates [31]. Nevertheless, these approaches have the serious drawback of forming an excessively thick solid electrolyte interphase (SEI) layer at the interface between the electrode and the electrolyte, owing to the high specific surface area [32], [33], [34]. As a result, the electrodes show a low first coulombic efficiency (CE). Furthermore, owing to their low tap density, nanocarbon-based electrodes are not suitable for commercial use, such as in electric vehicles.

In this study, we introduce a facile synthesis method for preparing anode materials based on commercial graphite composites. The graphite was modified through ball-milling and mild oxidation as mechanical and chemical procedures, respectively, to increase the number of exposed edges, which provides larger sites for MoSx loading. The MoSx grown in the opened interlayer gaps at the edges enhances the Li storage capacity of the material. The resulting MoSx embedded within ball-milled reduced graphite oxide (MoSx@B-rGtO) electrode showed a high specific capacity of 1239 mAh g−1 at a current density of 0.13 A g−1 and a retention capacity of 95% after 100 cycles (at 0.26 A g−1). The rate-capability of the composite was ~3.3 times that of pristine graphite at a high current density. Accordingly, we suggest that our graphite-based composite can be utilized as an anode material in LIBs.

Section snippets

Materials

Graphite flakes (natural, 99.8%) were purchased from Alfa Aesar. They were mildly oxidized in sulfuric acid (H2SO4, 95–98%) with potassium permanganate (KMnO4, ACS reagent grade, 99%) as the oxidizing agent. To remove the residual oxidizing agent, hydrogen peroxide (H2O2, 30%) was added to the solution. Ammonium tetrathiomolybdate ((NH4)2MoS4, 99.97%), as the MoSx precursor, and hydrochloric acid (HCl, ACS reagent grade, 36%) were used to synthesize the MoSx according to reaction formula (1)

Structural analysis of modified graphite

The structural changes in the B-Gt, GtO, and B-GtO were investigated using XRD and Raman spectroscopy. As shown in Fig. 2a, the structure of the mechanically modified B-Gt was similar to that of graphite, despite its larger specific surface area (458.4 cm2 g−1) than pristine graphite (Gt, 2.5 cm2 g−1), as shown in Fig. S1. However, the chemically modified GtO and mechanically/chemically modified B-GtO showed a (0 0 1) plane at 12–13° because the chemical oxidation resulted in an increase in the

Conclusions

A MoSx@B-rGtO anode with outstanding electrochemical performance was easily synthesized from graphite modified using ball-milling and a mild oxidation process. This approach significantly increased the number of edge sites on the graphite in which MoSx can effectively be embedded. In addition, various oxygen functional groups on the modified graphite led to a strong interaction between the MoSx and modified graphite. Electrochemical tests showed that the MoSx@B-rGtO electrode, which had high

CRediT authorship contribution statement

Youn-Ki Lee: Conceptualization, Validation, Investigation, Resources, Writing - Original Draft, Formal analysis, Visualization. Mihwa Lee: Conceptualization, Validation, Investigation, Resources, Writing - Original Draft, Formal analysis, Visualization. Gwan Won Lee: Investigation, Visualization. KwangSup Eom: Formal analysis, Writing - Review and Editing. Myong-Hoon Lee: Formal analysis, Writing - Review and Editing. Sungho Lee: Conceptualization, Writing - Review and Editing, Supervision,

Acknowledgements

This work was supported by a grant from the National Research Foundation of Korea (NRF) (NRF-2018M1A2A2061989 and NRF-2019M3E6A1064735), Human Resources Program in Energy Technology of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry and Energy, (No. 20194010201790 and No. 20193091010110) and the Korea Institute of Science and Technology (KIST) Institutional program, Carbon Cluster Development Program (No.

References (55)

  • H.W. Wang et al.

    XPS studies of MoS2 formation from ammonium tetrathiomolybdate solutions

    Surf. Coat. Technol.

    (1997)
  • M.A. Baker et al.

    XPS investigation of preferential sputtering of S from MoS2 and determination of MoSx stoichiometry from Mo and S peak positions

    Appl. Surf. Sci.

    (1999)
  • C.-L. Hsu et al.

    Enhancing the electrocatalytic water splitting efficiency for amorphous MoSx

    Int. J. Hydrog. Energy.

    (2014)
  • Z.-K. He et al.

    Reactive molten salt synthesis of natural graphite flakes decorated with SnO2 nanorods as high performance, low cost anode material for lithium ion batteries

    J. Alloy. Compd.

    (2019)
  • J. Yoon et al.

    High-performance ZnS@graphite composites prepared through scalable high-energy ball milling as novel anodes in lithium-ion batteries

    J. Ind. Eng. Chem.

    (2019)
  • K. Kang et al.

    Electrodes with high power and high capacity for rechargeable lithium batteries

    Science

    (2006)
  • Y. Mekonnen et al.

    A review of cathode and anode materials for lithium-ion batteries

  • T. Sasaki et al.

    Memory effect in a lithium-ion battery

    Nat. Mater.

    (2013)
  • M. Armand et al.

    Building better batteries

    Nature

    (2008)
  • W. Qi et al.

    Nanostructured anode materials for lithium-ion batteries: principle, recent progress and future perspectives

    J. Mater. Chem. A

    (2017)
  • V. Etacheri et al.

    Challenges in the development of advanced Li-ion batteries: a review

    Energy Environ. Sci.

    (2011)
  • K. Persson et al.

    Lithium diffusion in graphitic carbon

    J. Phys. Chem. Lett.

    (2010)
  • Q. Cjemg et al.

    Graphene-like-graphite as fast-chargeable and high-capacity anode materials for lithium Ion Batteries

  • N. Kim et al.

    Fast-charging high-energy lithium-ion batteries via implantation of amorphous silicon nanolayer in edge-plane activated graphite anodes

    Nat. Commun.

    (2017)
  • T. Stephenson et al.

    Lithium ion battery applications of molybdenum disulfide (MoS2) nanocomposites

    Energy Environ. Sci.

    (2014)
  • M. Chhowalla et al.

    The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets

    Nat. Chem.

    (2013)
  • T. Matsuyama et al.

    Electrochemical properties of all-solid-state lithium batteries with amorphous MoS3 electrodes prepared by mechanical milling

    J. Mater. Chem. A

    (2015)
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