Research On The Controllable Preparation, Microstructure And Lithium Storage Performance Of Iron-based Oxide Micro-nano Structure

With the development of electric vehicles and electrochemical energy storage markets,much attention has been paid to lithium-ion batteries?LIBs?with high energy density and long cycling lifetime.Iron oxides have been intensively studied because of their high theoretical capacity,environmental friendliness and abundant resource.However,there are still critical problems about iron oxides,including low electrical conductivity and drastic volume change during charge/discharge process,resulting in the poor cycle stability.This work aims at improving the lithium storage property of iron oxides by optimizing their microstructure.The main research contents and results are as follows.?1?Novel goethite??-FeOOH?corner-truncated tetragonal prisms?CTPs?with a length of about 1?m and a width of about 200 nm have been synthesized by a hydrothermal method.The morphology,structure and electrochemical properties of CTPs are systematically investigated.The obtained?-FeOOH CTPs exhibit high-quality single crystalline nature.In addition,the single?-FeOOH corner-truncated tetragonal prism?CTP?is enclosed by six side facets,two{020}and four{110}.The formation of?-FeOOH is associated with the growth and subsequent phase transformation ofb-FeOOH.The CTP contributes to the structural stability and avoids electrode pulverization.In addition,tiny crystallites are generated during the cycle,which increase the contact area between the electrode and electrolyte.Therefore,the?-FeOOH CTPs electrode displays excellent cycling performance with a reversible specific capacity of870 mAh g^-1 at 100 mA g^-1 after 100 cycles.?2?Porous Fe₂O₃ nanorods with tunable porosity are obtained by facile hydrothermal process and subsequent calcination at different temperatures.The morphology,porosity and structural stability of Fe₂O₃ nanorods are effectively controlled by a two-step strategy at nano/micrometer scale.Three different porous structures of Fe₂O₃ nanorods were obtained at 400,500 and 600oC,respectively.The pore size increases with the annealing temperature.Electrochemical performance tests show that the porous Fe₂O₃ electrode obtained by annealing at 500oC exhibits better cycling stability and rate capability than those obtained at 400 and 600oC.Most impressively,it delivers a capacity of 707.4 and687.7 mAh g^-1 at 1 and 2 A g^-1 after 200 cycles,respectively.Compared to the other two samples,the Fe2O3 nanorods obtained at 500oC have the optimized pore distribution and robust porous framework,which contributes to the structural and electrochemical stability of electrode.The porous framework can effectively alleviate the severe volume expansion/contraction and avoid pulverization of active materials,resulting in outstanding reversibility and rate capability.?3?FeOOH nanoparticles/reduced graphene oxide?FeOOH/rGO?composites are prepared by one-step hydrothermal method.When used as anode material for LIBs,the FeOOH/rGO composites exhibit better cycle stability and rate capabilities than FeOOH nanoparticles.The improvement in electrochemical performance can be attributed to the synergistic effect of FeOOH and rGO.The graphene nanosheets increase the electrical conductivity and could buffer the stress arising from volume change,which are conducive to the improvement of electrochemical performance of electrode.After 100cycles at 100 mA g^-1,the FeOOH/rGO composites deliver a capacity of about 490 mAh g^-1,which is much higher than that of pure FeOOH electrode.