Examining the Role of Anisotropic Morphology: Comparison of Free-Standing Magnetite Nanorods versus Spherical Magnetite Nanoparticles for Electrochemical Lithium-Ion Storage

As a matter of synthetic novelty, Fe₃O₄ (magnetite) nanorods (NRs) have been successfully generated by using a reproducible four-step protocol, wherein goethite is initially produced, morphologically tuned, chemically treated with a passivating agent to reduce aggregation, and ultimately converted to magnetite by thermal annealing within a reductive atmosphere. Our equally important objective was in correlating electrochemical behavior with the unique morphology of these Fe₃O₄ anode materials. As such, both conventionally coated and binder-free electrodes were tested using as-prepared magnetite NRs and nanoparticles (NPs) with controlled crystallite size as the active materials. Our study revealed that both the NR and NP Fe₃O₄ materials were amenable to effective binder-free electrode design. For the conventionally coated electrodes, the NR electrodes demonstrated an improved rate capability using a sequential discharge/charge current density profile as compared with that for corresponding NP electrodes. Most significantly, within the cycling stability test, the NR electrode delivered a high and stable capacity with a superior capacity retention relative to that of the NP for more than 50 cycles in half cells and 100 cycles in full cells. These data in particular showcase the undeniable benefits of the anisotropic structure of the material.