Elsevier

Electrochimica Acta

Volume 55, Issue 20, 1 August 2010, Pages 5975-5983
Electrochimica Acta

Lithium-ion battery anode properties of TiO2 nanotubes prepared by the hydrothermal synthesis of mixed (anatase and rutile) particles

https://doi.org/10.1016/j.electacta.2010.05.052Get rights and content

Abstract

From mixed (anatase and rutile) bulk particles, anatase TiO2 nanotubes are synthesized in this study by an alkaline hydrothermal reaction and a consequent annealing at 300–400 °C. The physical and electrochemical properties of the TiO2 nanotube are investigated for use as an anode active material for lithium-ion batteries. Upon the first discharge–charge sweep and simultaneous impedance measurements at local potentials, this study shows that interfacial resistance decreases significantly when passing lithium ions through a solid electrolyte interface layer at the lithium insertion/deinsertion plateaus of 1.75/2.0 V, corresponding to the redox potentials of anatase TiO2 nanotubes. For an anatase TiO2 nanotube containing minor TiO2(B) phase obtained after annealing at 300 °C, the high-rate capability can be strongly enhanced by an isotropic dispersion of TiO2 nanotubes to yield a discharge capacity higher than 150 mAh g−1, even upon 100 cycles of 10 C-rate discharge–charge operations. This is suitable for use as a high-power anode material for lithium-ion batteries.

Introduction

Recently, nanometer-sized active materials in the electrode of lithium rechargeable batteries, compared to conventional micrometer-sized materials, have attracted much attention due to the fast transport of lithium-ion species as facilitated by a shortened diffusion length. It is believed that such a design can bring a significant improvement in the electrochemical performance level of these batteries [1], [2]. Nanostructured TiO2 has been studied intensively in an effort to examine its lithium insertion behavior for use as an anode active material in lithium rechargeable batteries. These studies increased after TiO2-based active materials in these types of batteries were shown to have superior properties compared to other materials. These properties included higher capacity, a lower self-discharge rate, chemical stability, environmental benignancy, a low cost, and other advantages [3]. In particular, studies of TiO2 nanotubular anodes for use in lithium-ion batteries showed higher discharge/charge capacities, e.g., 305/200 mAh g−1 [4] corresponding to a lithium insertion coefficient x = 0.91/0.60 of LixTiO2 in a reaction of xLi+ + TiO2 + xe  LixTiO2.

Nanotubular TiO2 can be prepared by an alkaline hydrothermal reaction of TiO2 particles with nanocrystalline polymorphs. In particular, the formation of TiO2 nanotube or nanowire occurs by the heat treatment (annealing) of layered hydrogen titanate or protonated polytitanate (H2TinO2n+1·xH2O) previously ion-exchanged by HCl washing from sodium hydrogen titanate (NayH2−yTinO2n+1·xH2O). Sodium hydrogen titanate is the product of a hydrothermal reaction between TiO2 particles and a NaOH aqueous solution. It should also be noted that the shapes and electrochemical properties of nanotubular TiO2 strongly depend on the synthesis conditions, primarily the NaOH concentration and the annealing temperature. The best performance of nanotubular TiO2 as a lithium insertion material was reported from Bruce group [5], [6] who showed that TiO2(B) nanotube obtained via 15 M NaOH aqueous solution could achieve an initial discharge capacity of 328 mAh g−1 (x = 0.98). It was also shown that TiO2 particles with anatase [5], [6], [7], [8], rutile [4], [9], [10], [11], or a mixture of these two phases [12], [13] could be used as the starting material in the creation of nanotubular TiO2.

In this paper, TiO2 nanotubes are prepared by an alkaline hydrothermal method and subsequent annealing at 300–400 °C starting from TiO2 particles with various anatase:rutile compositions. As an anode active material for a lithium-ion battery, TiO2 nanotubes are characterized by a morphology analysis, crystalline properties evaluation, and by electrochemical investigations including cyclic voltammetry, impedance spectroscopy, and repeated discharge–charge tests. It is important to understand how the prepared TiO2 nanotubes show the superior electrochemical performance in association with their nanotubular structures.

Section snippets

Experimental

The starting TiO2 particles used in this study were anatase (titanium(IV) oxide, 100–200 nm, 3.1 g cm−3, Junsei) and rutile (titanium(IV) oxide, 200–500 nm, 3.9 g cm−3, Junsei) powders as supplied. The powder mixtures (sample code: R10, R7A3, R5A5, R3A7, and A10) were prepared by a simple physical blending process. In this process, R10 indicated 100 wt.% rutile and the R7A3 denoted a mixture consisting of rutile 70 wt.% and anatase 30 wt.%. These sample codes were also used when the corresponding

Results and discussion

Titanate nanotubes obtained after an alkaline hydrothermal reaction generally exhibit open ends and a length in the micrometer-order. After annealing at a temperature higher than 300 °C, titanate nanotubes can take on a nanowire shape through a decrease in their diameter and an increase in their length. The diameter and number of walls in titanate nanotubes can be determined according to the condition that best minimizes the excess surface energy caused by the imbalance between the ion

Conclusions

In this paper, TiO2 nanotubes are prepared by an alkaline hydrothermal reaction and a subsequent annealing process from mixed (anatase and rutile) particles. Their physical and electrochemical properties are then characterized for use as an anode active material for lithium-ion batteries. The morphology and a crystalline property analysis show that anatase TiO2 nanotubes containing minor TiO2(B) phase appear in spite of the anatase:rutile composition of the starting particles. It is also

Acknowledgements

This research was supported by the Converging Research Center Program through the National Research Foundation of Korea (NRF) funded by the Korea Ministry of Education, Science and Technology (2009-0082120).

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