Elsevier

Materials Characterization

Volume 96, October 2014, Pages 13-20
Materials Characterization

Anion-controlled synthesis of TiO2 nano-aggregates for Li ion battery electrodes

https://doi.org/10.1016/j.matchar.2014.07.005Get rights and content

Highlights

  • Nano-sized anatase TiO2 was synthesized using surfactant-free hydrolysis method.

  • The sizes of TiO2 were systematically tuned by controlling the ratio of anion.

  • Each TiO2 particle consists of an aggregation of 5 nm primary crystallites.

  • The capacity of the TiO2 NA which were 50 nm in size was 171 mAh g 1 at 100 cycles.

  • More than 0.5 Li was inserted into TiO2, which indicates good rate capability.

Abstract

Nano-sized anatase TiO2 was synthesized using surfactant-free hydrolysis method by controlling the ratio of anions in solution. The particle sizes of TiO2 were systematically tuned by the molar ratio of the Ti4 + precursors (chlorides and sulfates). Each TiO2 particle consists of an aggregation of 5 nm primary crystallites, resulting in a large specific surface area. TiO2 nano-aggregates (TiO2 NAs) which were 50 nm in size exhibited the best cycle stability. After calcination, the capacity of the TiO2 NA was enhanced to 171 mAh g 1 at 100 cycles at a rate of 0.2 C due to the removal of impediments such as a hydroxyl group and physisorbed water, indicating that more than 0.5 Li was inserted into TiO2 at 100 cycles, and that these NAs had good rate capability at high current densities.

Introduction

Titanium dioxide (TiO2) has been studied in a wide range of applications, such as solar cells [1], photocatalysts [2], gas sensors [3] and energy-storage devices [4], [5], due to its low cost, high stability, general abundance, and non-toxicity [6]. In the case of bulk TiO2, generally, the maximum insertion number of Li into TiO2 is 0.5 (Li0.5TiO2); thus, the theoretical capacity is 168 mAh g 1. However, TiO2 particles for which the particle size is in the nano-regime (below 100 nm) change the electrochemical reactivity toward Li, increasing the electrode/electrolyte contact area and shortening the path distance for both electron and ion transport. This induces more than 0.5 Li insertion into TiO2 [7], [8], [9], [10]. Some interesting approaches for TiO2-based nano-structure materials such as nano-rods [11] and nano-tubes [12], [13], [14], which insert more than 0.5 Li as well, have been devised to operate Li-ion batteries (LIBs) at high power and high energy levels. Therefore, nano-structured and nano-sized TiO2 is regarded as an alternative to carbon-based anode materials in LIBs [15], [16].

Meanwhile, other reports have attempted to synthesize spherical TiO2 using Ti(SO4)2 [17], [18]. Among them, Wei et al. reported the synthesis of spherical anatase TiO2 powder by a hydrolysis method using a Ti(SO4)2 source [19], but the TiO2 particle size did not change below 100 nm, and the particle size was irregular. In our previous research, we synthesized nano-sized and size-tunable spherical aluminum hydrous oxide using a hydrolysis method by controlling the anion ratios without a surfactant [20].

However this hydrolysis synthesis of size-tunable, nano-sized TiO2 has rarely been addressed compared to other common oxides. In this paper, various controlled sizes of anatase TiO2 nano-aggregates (NAs) are successfully synthesized by changing the ratio of chloride and sulfate anions using a hydrolysis method at a low temperature (80 °C). The overall synthetic procedure of the TiO2 NAs is illustrated in Scheme 1. When synthesized, additives such as a template or a surfactant were not used. Furthermore, the electrochemical performances of anatase TiO2 NAs below 100 nm in size were evaluated for the application to LIB electrodes. The anatase TiO2 NAs calcined at 400 °C exhibited enhanced Li reversible storage capacities.

Section snippets

Material Synthesis

Nano-sized anatase TiO2 was synthesized by a hydrolysis method. TiCl4 (JUNSEI) and Ti(SO4)2·nH2O (extra-pure, JUNSEI) were dissolved in a 100 ml of cold deionized water. To synthesize the size-tunable anatase TiO2 NAs, the total concentration of Ti4 + was fixed at 0.001 mol and the ratio of the TiCl4 and Ti(SO4)·nH2O was changed (hereafter Cl/SO42 :R). After aging in a refrigerator for 2 h, the solution was reacted in an oil bath at 80 °C for 30 min. After the reaction, the obtained product was

Synthesis of Size-Tunable Anatase TiO2 NAs

Regarding the preparation of various sizes of TiO2 NAs, the anion ratios are listed in Table 1. Fig. 1 shows SEM and TEM images of TiO2 NAs with various reaction conditions. Although some particles show a tendency to grow while adhering originally to each other, i.e., not necking, due to the high hydrolysis rate of TiO2, each particle has a relatively uniform and spherical shape. More importantly, the particle size of the spherical TiO2 NAs was reduced as the ratio of chloride anions was

Conclusions

In summary, we synthesized facile, additive-free and size-controllable anatase TiO2 NAs between 150 nm and 20 nm in size by changing the ratio of the anion concentration. As the concentration of chloride ions was increased, the size of the TiO2 NAs was reduced, with each NA consisting of an aggregation of tiny primary crystallites whose sizes were about 5 nm, which resulted in a large specific surface area.

The electrochemical performances of the TiO2 NAs as an anode material for LIBs were also

Acknowledgments

This work was supported by the Global Frontier R&D Program on Center for Multiscale Energy System funded by the National Research Foundation under the Korean Ministry of Education, Science and Technology (2013-052268), and the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2012R1A2A2A01045382 and 2010-0029027). The characterization of the materials was supported by the Research Institute of Advanced Materials (RIAM).

References (47)

  • Y.H. Jin et al.

    Tailoring high-surface-area nanocrystalline TiO2 polymorphs for high-power Li ion battery electrodes

    Electrochim. Acta

    (2010)
  • V. Subramanian et al.

    Nanocrystalline TiO2 (anatase) for Li-ion batteries

    J. Power Sources

    (2006)
  • P. Krtil et al.

    Lithium insertion into self-organized mesoscopic TiO2 (anatase) electrodes

    Solid State Ionics

    (2000)
  • B.L. He et al.

    Preparation and electrochemical properties of Ag-modified TiO2 nanotube anode material for lithium-ion battery

    Electrochem. Commun.

    (2007)
  • B. O'Regan et al.

    A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films

    Nature

    (1991)
  • M.R. Hoffmann et al.

    Environmental applications of semiconductor photocatalysis

    Chem. Rev.

    (1995)
  • L.L. Fields et al.

    Room-temperature low-power hydrogen sensor based on a single tin dioxide nanobelt

    Appl. Phys. Lett.

    (2006)
  • S.Y. Huang et al.

    Rocking chair lithium battery based on nanocrystalline TiO2 (anatase)

    J. Electrochem. Soc.

    (1995)
  • J.M. Tarascon et al.

    Issues and challenges facing rechargeable lithium batteries

    Nature

    (2001)
  • J. Maier

    Nanoionics: ion transport and electrochemical storage in confined systems

    Nat. Mater.

    (2005)
  • A.S. Arico et al.

    Nanostructured materials for advanced energy conversion and storage devices

    Nat. Mater.

    (2005)
  • J. Liu et al.

    Oriented nanostructures for energy conversion and storage

    ChemSusChem

    (2008)
  • J. Kim et al.

    Rate characteristics of anatase TiO2 nanotubes and nanorods for lithium battery anode materials at room temperature

    J. Electrochem. Soc.

    (2007)
  • Cited by (9)

    • Li<inf>2</inf>MnSiO<inf>4</inf> nanorods-embedded carbon nanofibers for lithium-ion battery electrodes

      2015, Electrochimica Acta
      Citation Excerpt :

      The high-temperature (55 °C) performance of the LMS/CNFs for LIBs was evaluated at scan rates of 0.05–0.5 C (Fig. S7 in the Supporting Information). In the initial step, the LMS/CNFs exhibit higher charge and discharge capacities than the theoretical capacity; this is attributed to unintended side reactions or to the formation of a solid electrolyte interface layer [32,33]. The discharge capacity of 145 mA h g−1 is also somewhat higher than that measured at room temperature and the discharge capacity is 88 mA h g−1 at 0.5 C. Capacity fading is, however, quite evident at this temperature (55 °C).

    • Reversible Li-storage in Titanium(III) Oxide Nanosheets

      2015, Electrochimica Acta
      Citation Excerpt :

      This represents an 86% increase compared to B-Ti2O3. The current density of all redox peaks are increased compared to B-Ti2O3 (Fig. S3 in the Supporting Information), which means that NS-Ti2O3 exhibited higher Li electroactivity than B-Ti2O3 as the particle size was reduced [14]. It is considered that Li+ ions partially diffuse into the interior of the bulky B-Ti2O3 powder.

    View all citing articles on Scopus
    View full text