Correlating Preparative Approaches with Electrochemical Performance of Fe3O4-MWNT Composites Used as Anodes in Li-Ion Batteries

Abstract

Fe3O4 nanoparticles (NPs) with an average size of 8–10 nm and a loading ratio of 50 wt% have been successfully attached onto the external surfaces of multi-walled carbon nanotubes (MWNTs) by means of three different preparative approaches, namely a sonication method, a covalent attachment protocol, as well as a non-covalent π-π interaction strategy. Specifically, the Fe3O4 NPs associated with the sonication method lie directly on the outer surfaces of the MWNTs. Particles covalently attached onto the MWNTs formed amide chemical bonds through the mediation of the amorphous (3-aminopropyl) triethoxysilane (APTES) linker. Finally, particles were anchored non-covalently onto the underlying conjugated MWNTs via an aromatic 4-mercaptobenzoic acid (4-MBA) linker. Both structural and electrochemical characterization protocols have been used to systematically correlate the electrode performance with the corresponding attachment strategies. Fe3O4-MWNT composites generated by the π-π interaction strategy delivered 813, 768, 729, 796, 630, 580, 522, and 762 mAh/g under rates of 200, 400, 800, 100, 1200, 1600, 2000, and 100 mA/g, with 72% retention between cycles 2 and 80, demonstrating both higher capacity and better cycling stability as compared with analogues derived from the physical sonication as well as covalent attachment strategies. This finding may be attributed to the enhanced charge and ion transport coupled with retention of physical contact with the underlying MWNTs after a large volume change during cycling. Our collective results suggest that the non-covalent π-π attachment modality is a more effective preparative strategy for enhancing the performance of MWNT-Fe3O4 composite electrodes after a full discharge process.