Uniform hematite nanocapsules based on an anode material for lithium ion batteries

doi:10.1016/j.elecom.2009.12.040

Electrochemistry Communications

Volume 12, Issue 3, March 2010, Pages 382-385

https://doi.org/10.1016/j.elecom.2009.12.040 Get rights and content

Abstract

Uniform α-Fe₂O₃ nanocapsules with a high surface area were synthesized by a novel wrap–bake–peel approach consisting of silica coating, heat treatment and finally the removal of the silica coating layer. The length, diameter and shell thickness of the hematite nanocapsules were about 65, 15 and 5 nm, respectively. The electrochemical properties of the α-Fe₂O₃ nanocapsules were investigated by cyclic voltammetry and charge/discharge measurements. The α-Fe₂O₃ nanocapsules showed a high reversible capacity of 888 mAh/g in the initial cycle and 740 mAh/g after 30 cycles as well as good capacity retention. This excellent electrochemical performance was attributed to the high surface area, thin shell and volume space of the hollow structure.

Introduction

In recent years, nanostructured 3d-metal oxides MO_x (M = Cu, Mn, Fe, Co, Ni, etc.) have been widely studied as anode materials for lithium-ion battery (LIB) owing to their high energy capacity [1], [2]. The properties of nanomaterials strongly depend on their size and morphology. By controlling the particle size, the quantization effect was widely examined and the surface area and robustness was influenced by modifying the particle shape. Hence, research attention has focused on controlling the nanoparticle size, shape and structure in order to attain unique properties for LIB [3]. Above all, interest on the 3-dimensional hollow sphere has focused on the prominent position on account of the high surface area and porous structure [4].

In terms of materials, hematite (α-Fe₂O₃) is considered a promising active lithium intercalation host due to its high theoretical capacity (1007 mAh/g), environmental friendliness, and low cost. As the particle size and morphology of hematite nanostructures exert a key influence on their electrochemical performance for lithium storage, hematite nanostructures showing different morphologies and particle sizes have been synthesized in order to enhance the electrochemical performance [5], [6].

In a similar context, the hollow nanostructured hematite possesses several advantages for LIB application such as the extended contact area between the active material and the electrolyte caused by their high surface area, the short lithium diffusion length resulting from the thin shell and the hollow space in the central part that buffers the volume expansion during cycling.

We developed a new route for synthesizing uniform-sized hematite nanocapsules with a high surface area and thin shell in order to achieve excellent electrochemical reactivity toward lithium. Stable, enhanced electrochemical performance due to the peculiar hematite nanocapsules was achieved.

Section snippets

Experimental

In a typical synthetic procedure of spindle-shaped β-FeOOH nanoparticles, 0.02 M FeCl₃·6H₂O was dissolved into 2 L of deionized water at 80 °C under magnetic stirring and the particles were washed with water. To perform the silica coating of the β-FeOOH nanoparticles, 300 ml of ammonium hydroxide (30 wt.%) was added to a solution containing 5 L of ethanol and 500 ml of deionized water. After being pre-coated with polyvinylpyrrolidone, the as-prepared β-FeOOH nanoparticles were dispersed in the

Results and discussion

The typical XRD patterns of the β-FeOOH nanorod and hematite nanocapsules are shown in Fig. 2a and b. All the diffraction peaks of Fig. 2a can be readily indexed to a pure tetragonal phase of β-FeOOH, which agrees well with the standard values (JCPDS 75-1594). After wrap–bake–peel procedure, the β-FeOOH nanoparticle was entirely converted into rhombohedral hematite (α-Fe₂O₃) structure (JCPDS 33-0664), as shown in Fig. 2b. The diffraction pattern shown in Fig. 2b indicates that the (1 1 0)

Conclusion

Hematite nanocapsules with a uniform diameter of 14 nm, length of 65 nm and shell thickness of 5 nm were prepared by a wrap–bake–peel process. The α-Fe₂O₃ nanocapsules exhibited excellent electrochemical performance, with an initial capacity of 888 mAh/g and a capacity retention of 84% after 30 cycles, due to the high surface area induced by the hollow nanostructure, the restriction of volume expansion along the limited inner volume and the short lithium diffusion length resulting from the thin

Acknowledgments

This work was supported by the WCU program through the National Research Foundation of Korea funded by the Ministry of Education, Science & Technology (R31-10013), the Division of Advanced Batteries in the NGE (Next generation engine) Program (Project No. 10028960-2007-11) and the Korean Ministry of Education, Science and Technology through the National Creative Research Initiative Program of the Korea Science and Engineering Foundation (KOSEF).

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Uniform hematite nanocapsules based on an anode material for lithium ion batteries

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusion

Acknowledgments

Mater. Res. Bull.

Electrochem. Acta

Nature

Adv. Funct. Mater.

J. Phys. Chem. B