Rationally designed carbon-coated Fe₃O₄ coaxial nanotubes with hierarchical porosity as high-rate anodes for lithium ion batteries

Fe₃O₄ is a promising high-capacity anode material for lithium ion batteries, but challenges including short cycle life and low rate capability hinder its widespread implementation. In this work, a well-defined tubular structure constructed by carbon-coated Fe₃O₄ has been successfully fabricated with hierarchically porous structure, high surface area, and suitable thickness of carbon layer. Such purposely designed hybrid nanostructures have an enhanced electronic/ionic conductivity, stable electrode/electrolyte interface, and physical buffering effect arising from the nanoscale combination of carbon with Fe₃O₄, as well as the hollow, aligned and hierarchically porous architectures. When used as an anode material for a lithium-ion half cell, the carbon-coated hierarchical Fe₃O₄ nanotubes showed excellent cycling performance with a specific capacity of 1, 020 mAh·g^-1 at 200 mA·g^-1 after 150 cycles, a capacity retention of ca. 103%. Even at a higher current density of 1, 000 mA·g^-1, a capacity of 840 mAh·g^-1 is retained after 300 cycles with no capacity loss. In particular, a superior rate capability can be obtained with a stable capacity of 355 mAh·g^-1 at 8, 000 mA·g^-1. The encouraging results indicate that hierarchically tubular hybrid nanostructures can have important implications for the development of high-rate electrodes for future rechargeable lithium ion batteries (LIBs).