Elsevier

Journal of Power Sources

Volume 196, Issue 16, 15 August 2011, Pages 6898-6901
Journal of Power Sources

Short communication
Effect of particle size on the phase behavior of Li-intercalated TiO2-rutile

https://doi.org/10.1016/j.jpowsour.2010.12.081Get rights and content

Abstract

With the aid of ab initio calculations, we compare the phase behavior upon lithiation of rutile particles of different sizes and morphologies. A rationale for the differences in their structural behavior is provided by combining concepts from Crystal Field Theory and semi-empirical concepts, such as bond length variation, minimal volume expansion, with accounts for the effects of diffusion and the anisotropy of the Li-distribution. It is shown that the phase behavior of spaghetti-like nano-particles differs from bulk rutile as a result of an extended single phase insertion domain and increased disorder of Li-ions. As Li-ions strive to minimize their repulsions by increasing their mutual separation a regular network of Li-ions is formed, being a precursor to the transformation of the rutile host lattice into spinel.

Introduction

For decades rutile structured titanium dioxide has been disregarded for applications as an anode since at normal conditions Li-uptake by polycrystalline rutile is insignificant [1]. An exception was the report of Li-insertion to high concentration at elevated temperatures [2]. Interest in this material has been sparked recently, when a high Li-uptake was observed at normal conditions for nanostructured rutile [3], [4], [5], [6], [7], [8].

The striking temperature dependence of intercalation behavior of bulk rutile has been rationalized in terms of limitations imposed by diffusion of Li-ions on the observed thermodynamics of Li-insertion [9]. Using ab initio simulations, it was shown that the limiting step is associated with restricted access to stable Li-sites upon single phase insertion up to Li-concentrations x = [Li]/[Ti]∼0.2 due to a highly anisotropic Li-diffusion [9], [10]. At elevated temperature and in small particles Li-diffusion is activated enabling access to the stable sites and intercalation occurs to much higher Li-concentrations. It appeared that diffusion controlled Li-insertion is not specific for TiO2 rutile, but occurs in a wider range of transition metal oxides, including TiO2-brookite [11], [12], TiO2–B (at elevated Li-concentrations [13], [14]) as well as some other rutiles (MnO2 [15], VO2 [16]).

More recently it has been found that the phase behavior of lithiated rutile may be influenced by the shape of nano-particles [3], [4], [7]. While Li-intercalation into nanostructured rutile follows the bulk behavior at elevated temperature [3], the phase transformations upon lithiation of specially tailored (spaghetti-like) nano-particles are different [4], [5], [6], [7]. In both cases, initial insertion is a single phase reaction, to x  0.2 [2], [3] and ∼0.4–0.5 [4], [7], respectively, which, however, is followed by a different sequence of phase transformations. While in the former case a monoclinically distorted rutile (Li0.75TiO2) and a layered hexagonal LiTiO2 phase [2], [3], [17] are formed, spaghetti-like nano-particles transform to a spinel structured titanate (Li0.5TiO2) and a rock-salt LiTiO2 [7]. The reasons for these different structural behaviors are at present not understood. Here, with the aid of ab initio simulations, we aim to rationalize the phase behavior of intercalated rutile and to get insights into the underlying mechanisms.

Section snippets

Details of calculation

All calculations were performed within the framework of density functional theory as implemented in the CASTEP software, within the pseudopotential plane-wave formalism [18]. Electron exchange and correlation effects are treated within the spin polarized generalized gradient approximation [19] with ultrasoft pseudopotentials [20] used to replace the Ti (1s, 2s, 2p), O (1s), and Li (1s) core orbitals. This set-up results in calculated cell parameters within 1% from the experimental values for

Li-intercalation into bulk rutile

Rutile is built from pillars of TiO6 octahedra, in which each octahedron shares two opposite edges. The pillars are joined by corners to form a tetragonal structure with straight channels along the tetragonal axes (the c-direction) (Fig. 1), where intercalated lithiums can be accommodated in vacant interstitial sites. In polycrystalline rutile Li-ions are inserted along the c-direction and have a high mobility along c-channels [9], [10], [24], [25]. The ordering of Li-ions in bulk rutile has

Conclusions

Using ab initio simulations we have shown that nanoparticles of rutile of a special shape (spaghetti-like) can display a phase behavior distinctly different from that of the bulk or nanostructured rutile. On the nano-scale the boundary of the single phase reaction, displayed at low Li-concentrations in the bulk, shifts to higher Li-concentrations enabling an alternative structural evolution upon intercalation. As Li-ions strive to form a regular network at these concentrations, rutile undergoes

Acknowledgments

This research was funded by the EPSRC under grant nos. EP/C545222 and EP/C54521.

References (29)

  • B. Zachau-Christiansen et al.

    Solid State Ionics

    (1988)
  • W.J. Macklin et al.

    Solid State Ionics

    (1992)
  • M.A. Reddy et al.

    Electrochem. Commun.

    (2006)
  • E. Baudrin et al.

    Electrochem. Commun.

    (2007)
  • H. Qiao et al.

    Electrochem. Commun.

    (2008)
  • D. Munoz-Rojas et al.

    Solid State Ionics

    (2007)
  • M.V. Koudriachova et al.

    Chem. Phys. Lett.

    (2003)
  • M.V. Koudriachova

    Chem. Phys. Lett.

    (2008)
  • M.V. Koudriachova et al.

    Solid State Ionics

    (2004)
  • M.V. Koudriachova et al.

    Solid State Ionics

    (2003)
  • M.V. Koudriachova et al.

    Comput. Mater. Sci.

    (2002)
  • R.J. Cava et al.

    J. Solid State Chem.

    (1984)
  • H. Uchiyama et al.

    Solid State Ionics

    (2009)
  • D.H. Wang et al.

    Chem. Mater.

    (2008)
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