Controlled Synthesis And Electrochemical-performance Studies Of Monocrystalline Porous Iron Oxides Particles

Iron oxides have high theoretical capacity, low cost and environmental affinity, which make them promising candidates as anode materials for high energy-density lithium-ion batteries. However, the charge/discharge cycling performance of the iron oxides is unsatisfied, because of volume change of the iron oxides during lithiation/delithiation process. In order to improve cycling performance of iron oxides, in this study, monocrystalline porousα-Fe2O3 particles with tunable size have been synthesized through pH adjustment of the FeCl3 solutions via a hydrothermal process. The morphology, size, BET specific surface area and microstructure of the monocrystalline porousα-Fe2O3 particles have been characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution electron microscopy and N2 absorption. The size of the 350℃calcinedα-Fe2O3 particles could be tuned from 925.6±98.2 nm to 43.4±5.8 nm when pH of the solution was increased from initial 1.8 to 9.3. The BET specific surface areas of theα-Fe2O3 particles with size of 925.6 nm and 43.4 nm are 3.97 m2g-1 and 26.04 m2g-1, respectively. Theα-Fe2O3 particles with size of 925.6 nm exhibit porous structure, where the pores are mainly composed of mesopores and macropores. While theα-Fe2O3 particles with size of 43.4 nm display micropore structure. The charge/discharge cycling performance of theα-Fe2O3 particles with size of 43.4 nm is better that theα-Fe2O3 particles with size of 925.6 nm at current density of 0.1C. Their initial discharge capacity/50th charge capacities are 1253.7 mAhg-1/835.9 mAhg-1 and 1055.7 mAhg-1/566.1 mAhg-1, respectively. However, when the current densities were increased to 0.3C,1C and 3C, the cycling performance of theα-Fe2O3 particles with size of 925.6 nm is much better that theα-Fe2O3 particles with size of 43.4 nm. Their charge capacity at the 50th cycle under condition of 0.3C 1C and 3C are 582.7 mAh·g-1/437.2 mAh·g-1/400 mAh·g-1 and 413.5 mAh·g-1/240.3 mAh·g-1/178.5mAh·g-1, respectively.Micro-sized (1030.3±178.4 nm) porous and nano-sized (50.4±8.0 nm) solid Fe3O4 particles have been fabricated through hydrogen thermal reduction of the as-synthesizedα-Fe2O3 particles. The nano-sized solid Fe3O4 particles exhibit capacity fading with charge/discharge cycling, and with charge capacity of 353 mAhg-1 and capacity retention of only 32.6% at the 50th cycle. Whereas, the micro-sized porous Fe3O4 particles display very stable cycling performance, with charge capacity of 684.4 mAh·g-1 and capacity retention of 77.1% at the 50th cycle.The good rate-capacity performance of the porous a-Fe2O3 particles with size of 925.6 nm and the stable cycling performance of the micro-sized porous Fe3O4 particles are due to their unique monocrystalline porous structure, which make them promising candidates as anode materials for high energy-density lithium-ion batteries.