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A Facile Approach to Prepare Rattle/Hollow-Type α-Fe2O3 Submicron Spheres with a Thin Carbon Layer for High-Performance Lithium Ion Battery Anodes

Tuesday, 10 June 2014
Cernobbio Wing (Villa Erba)
H. S. Lim (Department of Chemical Engineering, College of Engineering, Hanyang University), Y. K. Sun (Energy Engineering, Hanyang University, Seoul, Korea), and K. D. Suh (Department of Chemical Engineering, College of Engineering, Hanyang University)
Recently, the hollow structures of various transition metal oxide materials (cobalt oxides [1], iron oxides [2], nickel oxides [3]) have received particular attention for use in lithium-ion batteries (LIBs) because they not only have a higher theoretical capacity than commercial graphite (372 mAh g-1), but also possess a large void space that can accommodate huge changes in volume during electrochemical reactions. In our previous report, hollow Fe3O4 microspheres exhibited the improvement of cyclability. Although the hollow Fe3O4 microspheres show remarkable improvement in cycling stability, most still exhibited capacity fading at high current rates due to their poor electrical conductivity. In order to improve cycling performance at high current rates, we have prepared rattle/hollow-type α-Fe2O3 submicron spheres with thin carbon layer through the diffusion of metal ions into the hydrogel template. In this synthetic process, an additional carbon coating process is not necessary such as two-step hydrothermal process and chemical vapour deposition (CVD). In addition, we report a strategic synthesis method to control the internal structures of α-Fe2O3 submicron spheres. Of the two types of samples, the rattle-type α-Fe2O3 submicron spheres have a high surface area (1415 m2 g-1) because α-Fe2O3 nano-grains are formed in polymer networks. During removal process of template particles by heat treatment, because the cross-linked networks surrounding tiny Fe metal precursors act as a barrier to prevent particle growth, the rattle structured α-Fe2O3 submicron spheres consisting of nano-sized grains with a high surface area can be formed. In this process, the thin carbon layer is formed on the inside surface as well as outer surface of the α-Fe2O3 nano-grains, which was generated from a decomposition of the polymer templates. These rattle/hollow α-Fe2O3 submicron spheres with thin carbon layer exhibit excellent cyclability at high current rates (~10C). We demonstrated that the void space and thin carbon layer covering most of the α-Fe2O3 surface acts as buffer layer to accommodate variation in the volume of α-Fe2O3 and improves charge transfer at high current rates.

References

[1] J. Wnag, N. Yang, H. Tang, A. Dong, A. Jin, M. Yang, D. Kisailus, H. Zhao, Z. Tang and D. Wang, Angew. Chem. Int. Ed., 2013, 52, 6417.

[2] H. –S. Lim, B. –Y. Jung, Y. –K. Sun, K. –D. Suh, Electrochimica Acta, 2012, 75, 123.

[3] N. H. Idris, J. Mater. Res., 2011, 26, 860.