Synthesis And Electrochemical Performance Of Fe₃O₄/MWNTs Nanocomposites For Anodes In Lithium Ion Batteries

Lithium ion batteries (LIBs) are becoming the most widely used energy resource in portable electronic devices due to their high energy density, fast charge-discharge rate, and excellent cycling performance. However, commercial graphene anode materials normally have low theoretical capacity (372 mAh g-1), which severely limits the application of LIBs in the electric vehicles and hybrid electric vehicles. Great efforts have been made to explore anode materials with high reversible capacity for LIBs.Fe3O4 has been regarded as one of the most promising anode materials for LIBs owing to its high theoretical specific capacity (925 mAh g-1), natural abundance and environmental benignity.Carbon nanotubes (CNTs) have attracted wide attentions as additives in constructing hybrid nanocomposites due to their superior electrical conductivity, high surface-to-volume ratio, ultrathin walls, and structural flexibility. Their large specific surface area ensures high contact area between electrolyte and electrode, and the ultrathin walls shorten the Li-ion diffusion distance. In addition, CNTs can be well connected to form unique conductive networks to provide continuous conductive pathways for electron transport. The CNTs can serve as not only conducting materials, but also an excellent inert confining buffer to accommodate the strain of volume change during the rapid charge/discharge processes.Therefore, enhanced electrode performance can be achieved through the application of these unique electrode structures by incorporating transition metal oxides with CNTs. The combination of conductive network of CNTs and high capacity of Fe3O4 nanoparticles is a promising way to make anode materials with excellent electrode performance.In this study, two different methods were demonstrated to synthesize Fe3O4/MWNTs nanocomposites. The performances of Fe3O4/MWNTs nanocomposites as anode materials of lithium ion battery were investigated, which is specifically provided as follows:A novel solvothermal method in methanol-glycerol solvent followed by an annealing process in argon atmosphere was used to prepare the Fe3O4/MWNTs nanocomposites in this work. The prepared MWNTs nanocomposites with homogenously anchored nanomagnetite of 10～20 nm have demonstrated serving as anode materials for lithium ion batteries (LIBs) with a specific capacity of 829 mAh g-1 after 50 cycles at a current density of 100 mA g-1. And it delivers specific capacities of 714,686,624,541,408 and 294 mAh g-1 at current densities of 100,200, 400,800,1600 and 3200 mA g-1. The as-prepared electrode material exhibited superior electrochemical performance..Another novel solvothermal method in ethanol-glycol solvent was also used to prepare the Fe3O4/MWNTs nanocomposites in this work. At a current density of 100 mA g-1, the prepared multi-walled carbon nanotubes demonstrated a specific capacity of 600 mAh g-1 after 100 cycles,653 mAh g-1 after 200 cycles and 605 mAh g-1 after 300 cycles as anode materials for lithium ion batteries (LIBs). These Fe3O4/MWNTs nanocomposites showed excellent cycling performance.The superior electrochemical performances of the Fe3O4/MWNTs originate from the unique conductive network of MWNTs in the nanocomposites as well as the high capacity from the Fe3O4.