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I2.03 - Carbon-Coated ZnFe2O4 Nanocrystals for Advanced Lithium-Ion Anodes 
April 7, 2015   2:15pm - 2:30pm

As the leading battery technology, lithium-ion batteries (LIBs) have been widely used in consumer electronics. However, for future large-scale applications in electric or hybrid vehicles, further improvement would require concerning power and energy density demanded by such applications. Compared with the theoretical specific capacity of commercialized graphite (372 mAh/g) which is widely used as anode material in LIBs, the transition metal oxide shows great promise as they can provide much higher capacities and rate capabilities. For example, Zinc Ferrite (ZnFe2O4), which can be regarded as the replacement of one iron atom of Fe3O4 by zinc element, can provide an enhanced theoretical capacity of 1000mAh/g. To date, many efforts have been put on developing transition metal oxide based nanostructured-materials to enhance the rate performance. These nanostructures, such as nanoparticles, hollow nanospheres, nanotubes, etc., are effective in facilitating the Li ion diffusion due to a reduced diffusion length within the active materials and an increased electrolyte/electrode contact area. Moreover, carbon-based nanocomposites formed by carbon coating proved to enhance not only the ionic but also the electronic conductivity of electrode, which is very promising for high rate performances. Here we propose a general method to synthesize carbon-coated ZnFe2O4 nanocrystals with various nanostructures templated by star-like poly (acrylic acid)-block-polystyrene (PAA-PS) diblock copolymer and polystyrene-block-poly(acrylic acid)-block-polystyrene (PS-PAA-PS) triblock copolymer. Through a strong coordination bonding between the metal moiety of inorganic precursors and the functional groups of PAA (-COOH), ZnFe2O4 nanocrystals can be selectively incorporated into the space formed by the PAA block in star-like block copolymer templates. As a result, ZnFe2O4 nanoparticles and hollow nanospheres can be synthesized guided by the star-like PAA-PS and PS-PAA-PS templates, respectively. In addition, the size of ZnFe2O4 nanocrystals could be easily changed by varying the molecular weight of templates. The soft template not only serves as an easy control over the size and shape of ZnFe2O4 nanocrystals, but also acts as carbon source when calcinated at high temperature at argon atmosphere. We demonstrated that the carbon-coated ZnFe2O4 nanoparticles and hollow nanospheres obtained by the templating method would be superior anode materials for LIBs.

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