Preparation And Modification Of Iron Oxide Nanoarray And Their Lithium Storage Properties

As environment friendly anode materials for rechargeable lithium-ion batteries, iron oxides have been paid much attention because of their high theoretical capacities, safety, and low cost. However, like other metal oxides, iron oxides also suffer from poor rate capability and cycling stability, which is associated with its low conductivity and the large volume change, easy aggregation, causing pulverization and severe destruction of the electrode during the charging/discharging process. To overcome these drawbacks, one feasible approach is reasonable designing nanostructured electrode with merits of right accommodate the volume expansion, fast electrons and ions transportation, stable mechanical structure, and soforth. In this work, Cu/Fe3O4 nanoarrays, Cu-Fe2O3/C and Cu-Fe3O4/C hybrid nanoarrys have been successfully prepared on copper substrate by a Hydrolysis-induced Redox (HIR) strategy coupled with a simple calcination process. The as-prepared iron oxides nanoarrays can be used as anode for lithium ion batteries directly, which overcome the above drawbacks to a great extent and enhanced the lithium storage properties. In addition, the application of Cu/Fe3O4 nanoarrays in Fe3O4/LiFePO4 full cell has also been preliminarily explored. The main points are summarized as follows:1. Cu/Fe3O4 nanorod array has been prepared via combination of a facile Hydrolysis-induced Redox (HIR) strategy followed by a simple thermal reduction process. In contrast to conventional methods, the method has the merits of low cost, mild temperature, and simple process.The high conducting copper nanorod arrays on copper substrate within Cu/Fe3O4 nanoarrays form a well-ordered 3D nano current collector.Based on them, the Cu/Fe3O4 nanoarrays exhibit a superior cycling performance to that made of Fe3O4 nanorod powder when used as the electrodes for lithium ion batteries.The Cu/Fe3O4 nanoarray electrode can deliver a reversible capacity as much as 543.5 mAh g-1 after 500 cycles at a current density of 5 C with a high capacity retention of 86%.It also displays an excellent rate capability of 289.2 mAh g-1 at a rate of 15 C(1 C=1000 mAh g-1). The results suggest that the Cu/Fe3O4 nanoarray is a promising electrode for high energy density lithium-ion batteries.2. Cu2O-Fe(OH)3 nanotube arrays have been successfully fabricated by using FeCl2 solution as reducing agent and Cu(OH)2 nanorod array as template. The Cu-Fe2O3/C nanoarrays and Cu-Fe3O4/C nanoarrays were obtained by calcining Cu2O-Fe(OH)3 nanotube arrays with glusose coating in N2 and Ar/H2 atomosphere,respectively. The characterzation results showed that the as-prepared Cu-Fe2O3/C and Cu-Fe3O4/C keep well with uniform morphology, integrated nanoarray architecture.Electrochemical properties results show that, compared with the Cu2O-Fe2O3 nanoarrays, Cu-Fe2O3/C nanoarrays exhibit excellent rate performance, showing capacity of 510 mAh g-1 at 16 C high-rate. The Cu-Fe3O4/C nanoarrays also exhibit a superior performance compared with Cu-Fe3O4 nanoarrays, showing a rate capacity of 417 mAh g-1 at 16 C rate and high capacity retention of 131.7% after 200 cycles at 1.6 C rate. The above results indicated that the modified iron oxide nanoarrays with carbon coated can effectively improve their electrochemical properties in lithium ion battery.3. A hydrothermal reaction has been adopted to synthesize pure LiFePO4 first, which then was modified with carbon coating and magnesium ion (Mg2+) doping through a post-heat treatment.Energy dispersive spectroscopy mappings have verified the homogeneous existence of doped Mg2+ in LiFePO4 particles. The electrochemical test of the as-prepared cathode material shows that Mg2+ doped lithium iron phosphate exhibits high specific capacity (158.8 mAh g-1 at 0.1 C,1 C=150 mAh g-1), superior rate capability (77.2 mAh g-1 at 20 C rate) and enhanced cycle stability (200 cycles at rate of 1 C with capacity retention of 89.2%). The polarization and charge transfer resistance of the electrode have been reduced greatly through modification. This synthesis route is promising in making the hydrothermal method more practical for preparation of the LiFePO4 material and enhancement of electrochemical performance. Fe3O4/LiFePO4 full cell has also been successfully assembled based on self-prepared LiFePO4 cathode material and Cu/Fe3O4 anode.