10.1021/acsnano.5b00088.s001 Jung Sang Cho Jung Sang Cho Young Jun Hong Young Jun Hong Yun Chan Kang Yun Chan Kang Design and Synthesis of Bubble-Nanorod-Structured Fe<sub>2</sub>O<sub>3</sub>–Carbon Nanofibers as Advanced Anode Material for Li-Ion Batteries American Chemical Society 2015 volume change Fe 2O nanofibers Kirkendall effect electrochemical properties Fe 2O spheres electrospinning method electrospun precursor nanofibers target material Fe 2O nanospheres carbon matrix nanofibers results Advanced Anode Material Kirkendall diffusion process capacity retentions heating process Fe nanocrystals air atmosphere discharge capacities 2015-04-28 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Design_and_Synthesis_of_Bubble_Nanorod_Structured_Fe_sub_2_sub_O_sub_3_sub_Carbon_Nanofibers_as_Advanced_Anode_Material_for_Li_Ion_Batteries/2172790 A structure denoted as a “bubble-nanorod composite” is synthesized by introducing the Kirkendall effect into the electrospinning method. Bubble-nanorod-structured Fe<sub>2</sub>O<sub>3</sub>–C composite nanofibers, which are composed of nanosized hollow Fe<sub>2</sub>O<sub>3</sub> spheres uniformly dispersed in an amorphous carbon matrix, are synthesized as the target material. Post-treatment of the electrospun precursor nanofibers at 500 °C under 10% H<sub>2</sub>/Ar mixture gas atmosphere produces amorphous FeO<sub><i>x</i></sub>–carbon composite nanofibers. Post-treatment of the FeO<sub><i>x</i></sub>–carbon composite nanofibers at 300 °C under air atmosphere produces the bubble-nanorod-structured Fe<sub>2</sub>O<sub>3</sub>–C composite nanofibers. The solid Fe nanocrystals formed by the reduction of FeO<sub><i>x</i></sub> are converted into hollow Fe<sub>2</sub>O<sub>3</sub> nanospheres during the further heating process by the well-known Kirkendall diffusion process. The discharge capacities of the bubble-nanorod-structured Fe<sub>2</sub>O<sub>3</sub>–C composite nanofibers and hollow bare Fe<sub>2</sub>O<sub>3</sub> nanofibers for the 300th cycles at a current density of 1.0 A g<sup>–1</sup> are 812 and 285 mA h g<sup>–1</sup>, respectively, and their capacity retentions measured from the second cycle are 84 and 24%, respectively. The hollow nanospheres accommodate the volume change that occurs during cycling. The unique structure of the bubble-nanorod-structured Fe<sub>2</sub>O<sub>3</sub>–C composite nanofibers results in their superior electrochemical properties by improving the structural stability during long-term cycling.