Elsevier

Journal of Power Sources

Volume 304, 1 February 2016, Pages 119-127
Journal of Power Sources

Highly stable TiO2 coated Li2MnO3 cathode materials for lithium-ion batteries

https://doi.org/10.1016/j.jpowsour.2015.11.020Get rights and content

Highlights

  • We prepared Li2MnO3 cathode materials coated with TiO2 (OLO@TiO2).

  • The ratio of layered Li2MnO3 to anatase TiO2 was controlled.

  • The shell thickness in OLO@TiO2 was controlled.

  • OLO@TiO2 exhibited high specific capacity and improved high rate cycling performance.

Abstract

Many efforts have been made to improve the electrochemical performance of Li-rich cathode materials such as metal ion doping, surface modification, and fabricating nanostructured materials. Here, we demonstrate Li2MnO3 (denoted as OLO) cathode materials coated with TiO2 (OLO@ TiO2) for high-performance LIBs. The ratio of layered Li2MnO3 to anatase TiO2 as well as the shell thickness in the OLO@TiO2 cathodes were controlled by increasing the addition of titanium butoxide. The structure and chemical states for TiO2 coated OLO electrodes were confirmed using field-emission scanning electron microscopy, field-emission transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. To evaluate the performance of the electrodes for LIBs, charge/discharge curves, cycling performance, cyclic voltammograms, and Nyquist plots of the as-prepare cathode materials were obtained using lithium coin cells. In particular, since the TiO2 coating layer in OLO@TiO2 could stabilize the interface between the cathode and electrolyte, OLO@TiO2 exhibited high specific capacity, improved high rate cycling performance, and excellent cycle life due to the low interface resistance and high diffusion coefficient of lithium ion, compared with the uncoated OLO cathode.

Introduction

Lithium-ion batteries (LIBs) have been extensively utilized as a power source of portable electronics and electric vehicles with essential requirements such as high durability, high-energy density, and improved safety [1], [2], [3], [4], [5], [6]. In particular, since the development of high performance LIBs requires a remarkably increased capacity of cathode materials, Li2MnO3 cathode materials as an over-lithiated layered oxide (OLO) have recently attracted much attention due to their high theoretical capacity (>250 mAh g−1) and high potential (>4.5 V) [7], [8], [9], [10], [11]. It was reported that Li2MnO3 with a monoclinic symmetry (space group of C2/m) exhibited a high electrochemical capacity of 300 mAh g−1 due to the ordered distribution of Li and Mn in the transition metal layers [12], [13]. However, the activation process of Li2MnO3 at the initial charge to 4.8 V leads to a high capacity of the Li-rich layered cathodes accompanied with a low Coulombic efficiency of the first cycle [14], [15], [16], [17], [18]. The irreversible capacity loss may be attributed to the simultaneous removal of Li2O from the lattice of Li2MnO3 when charging beyond the oxidation of the valence of the transition metal ions above +4, thus resulting in the elimination of oxygen ion vacancies in the first charge process [19], [20], [21], [22], [23], [24], [25], [26]. The extraction of Li2O during the activation step can damage the cathode surface due to the increased cell impedance and decreased capacity particularly with increasing current rate. Furthermore, the oxidation of electrolytes at high potentials and the attack of acidic species such as hydrogen fluoride (HF) would lead to degradation of the electrode/electrolyte interface resulting in a deteriorated electrochemical performance [27], [28], [29], [30], [31], [32], [33], [34], [35].

Many efforts have been made to improve the electrochemical performance of Li-rich cathode materials, such as metal ion doping [23], [36], [37], [38], [39], [40], surface modification [25], [41], [42], [43], [44], [45], [46], [47], and fabricating nanostructured materials. Among these approaches, surface modification using Al2O3 [28], [48], AlPO4 [49], [50] and TiO2 [28], [33] has been carried out using a wet chemical process under a mild acidic atmosphere. The surface modified Li-rich cathodes have exhibited improved reversibility and cycleability in LIBs [24], [25], [26], [27], [28], [29], [30], [31], [51], [52]. Especially, TiO2 is considered to be one of the most promising coating materials due to a low production cost, large abundance, non-toxicity, and good structural stability for enhancing the electrochemical performance of Li-rich cathodes. The existence of the TiO2 coating layers in the Li-rich cathodes is believed to suppress the HF corrosion on the cathodes, since the oxidation reaction of TiO2 + 6HF + 2e → H2TiF6 + 2H2O is extremely difficult to react at room temperature. Herein, we prepared TiO2 coated Li2MnO3 cathodes for high-performance LIBs. The relative ratio of TiO2 to Li2MnO3 in the coated cathodes was elaborately controlled with increasing ratio of titanium butoxide. The structural characterization of TiO2 coated Li2MnO3 electrodes was carried out using field-emission scanning electron microscopy (FE-SEM), field-emission transmission electron microscopy (FE-TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). To evaluate the performance of the electrodes for LIBs, charge/discharge curves, cyclic voltammograms (CVs), cycling performance and Nyquist plots of the as-prepared cathode materials were obtained using lithium coin cells.

Section snippets

Synthesis of Li2MnO3

A Li2MnO3 cathode was synthesized using a quaternary medium consisting of water, cyclohexane (Aldrich), lithium dodecylsulfate (LDS, Aldrich) n-butanol (BuOH, Aldrich), and pluronic acid [P123, (PEO)20-(PPO)70-(PEO)20, where PEO is polyethylene glycol and PPO is polypropylene glycol; Aldrich]. The P123 (10.0 g) as a polymer template was dissolved in a mixed solution consisting of 80 g cyclohexane, 9.6 g n-butanol, 0.45 g of LDS, and 0.2 g Ketjen black and was completely stirred until it became

Results and discussion

Fig. 1 shows the wide-scan XRD patterns of the as-prepared pristine Li2MnO3 and Li2MnO3 cathode materials coated with TiO2 with an increasing addition of titanium butoxide from 50 to 200 mL (denoted as OLO-only, OLO@TiO2-50, OLO@TiO2-100, and OLO@TiO2-200). In general, the Li2MnO3 has a layered structure with a monoclinic unit cell and C2/m space group (PDF 81–1953). The lattice parameters of the OLO-only and OLO@TiO2 were in good agreement with the values presented in the literature for the

Conclusions

We prepared Li2MnO3 cathode materials coated with TiO2 for high-performance LIBs. The ratio of layered Li2MnO3 to anatase TiO2 and shell thickness in OLO@ TiO2 cathodes could be elaborately controlled with an increasing addition of titanium butoxide. In particular, the TiO2 coating layer in OLO@TiO2 was expected to stabilize the interface between the cathode and electrolyte, reducing the decomposition of electrolyte at a high voltage. As a result, the high specific capacity, improved high rate

Acknowledgments

This work was supported by the National Research Foundation of Korea Grant funded by the Korean Government (NRF-2013R1A1A2012541).

References (57)

  • J. Zhao et al.

    Hierarchical functional layers on high-capacity lithium-excess cathodes for superior lithium ion batteries

    J. Power. Sources

    (2014)
  • X. Liu et al.

    CaF2-coated Li1.2Mn0.54Ni0.13Co0.13O2 as cathode materials for Li-ion batteries

    Electrochimica Acta

    (2013)
  • J. Wang et al.

    Improving the electrochemical properties of high-voltage lithium nickel manganese oxide by surface coating with vanadium oxides for lithium ion batteries

    J. Power. Sources

    (2015)
  • J. Zheng et al.

    Improved electrochemical performance of Li[Li0.2Mn0.54Ni0.13 Co0.13]O2 cathode material by fluorine incorporation

    Electrochimica Acta

    (2013)
  • C.W. Park et al.

    Synthesis and materials characterization of Li2MnO3-LiCrO2 system nanocomposite electrode materials

    Mater. Res. Bull

    (2007)
  • Z.Q. Wang et al.

    Polaron states and migration in F-doped Li2MnO3

    Phys. Lett. A

    (2014)
  • M. Tabuchi et al.

    Mn source effects on electrochemical properties of Fe- and Ni- substituted Li2MnO3 positive electrode material

    J. Power Sources

    (2015)
  • Y. Wu et al.

    Simultaneous surface coating and chemical activation of the Li-rich solid solution lithium rechargeable cathode and its improved performance

    Electrochimica Acta

    (2013)
  • A. Klein et al.

    Improving the cycling stability of Li2MnO3 by surface treatment

    J. Power. Sources

    (2015)
  • M. Choi et al.

    Ultra-thin Al2O3 coating on the acid-treated 0.3Li2MnO3 ∙ 0.7LiMn0.60Ni0.25Co0.15O2 electrode for Li-ion batteries

    J. Alloy. Compd

    (2014)
  • X. Miao et al.

    Li2ZrO3-coated 0.4Li2MnO3∙0.6LiNi1/3Co1/3Mn1/3O2 for high performance cathode material in lithium-ion battery

    J. Power. Sources

    (2014)
  • T. Zhao et al.

    Design of surface protective layer of LiFFeF3 nanoparticles in Li-rich cathode for high-capacity Li-ion batteries

    Nano Energy

    (2015)
  • K.M. Shaju et al.

    X-ray photoelectron spectroscopy and electrochemical behaviour of 4V cathode, Li(Ni1/2Mn1/2)O2

    Electrochimica Acta

    (2003)
  • B.L. Ellis et al.

    Positive electrode materials for Li-Ion and Li-batteries

    Chem. Mater

    (2010)
  • H. Yu et al.

    J. Phys. Chem. Lett

    (2013)
  • G. Jain et al.

    Synthesis, electrochemistry, and structural studies of lithium intercalation of a nanocrystalline Li2MnO3-like compound

    Chem. Mater

    (2005)
  • M.M. Thackeray et al.

    Li2MnO3-stabilized LiMO2 (M = Mn, Ni, Co) electrodes for lithium-ion batteries

    J. Mater. Chem

    (2007)
  • C.S. Johnson et al.

    Synthesis, characterization and electrochemistry of lithium battery electrodes xLi2MnO3·(1-x)LiMn0.333Ni0.333Co0.333O2(0≤x≤0.7)

    Chem. Mater

    (2008)
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