The Preparation And Performance Study Of Transition Metal Oxide/Graphene Composites As Anodes For Lithium-Ion Batteries

In order to meet the needs of modern society and rapid industrial development,it is necessary to design high-efficiency,environmentally-friendly,and low-cost energy sources under the world energy use has increased sharply over the past several decades.Current commercially available graphitic carbon anode for lithium-ion batteries?LIBs?displays a even low theoretical capacity?372 m Ah g-1?,which could not satisfy the high power and energy density requirements of future energy storage devices.The 3d transition metal oxide compounds?Mx Oy,where M is Co,Ni,Cu or Fe?demonstrate high reversible capacity?¹000 m Ah g-1?,which are considered to be potential candidates as anode materials for LIBs.Nevertheless,as the inherent deficiencies of low essential electrical/ionic conductivity,large volume expansion and common powder agglomeration,all of 3d transition metal-oxides suffer from poor initial coulombic efficiency and lower capacity retention during prolonged cycling,which cause the unsatisfactory results.To overcome these challenges,there are generally two strategies to address these issues.One approach is to synthesize the heterostructures to mitigate the self defects,which have attracted considerable interests due to their long-cycle-life lithium storage.Another approach to overcome the challenges is to construct carbon/transition metal oxide compounds nanocomposites of 0 dimensional?0D?,1D,2D,and 3D structures to enhance the electric conductivity and structural stability.Graphene is a good choice due to unique 2D structure with excellent electrical,mechanical and thermodynamic performance in various conductive additives.Based on the above two aspects The research contents of this paper are as follows:?1?Ternary copper oxides-reduced graphene oxide?Cu2O-Cu O-RGO?composites were successfully synthesized in-situ by a self assembly solvothermal route in a water-ethanol mixture and used directly as anode materials for lithium ion batteries.The Cu2O-Cu O-RGO composites delivered a reversible capacity of 842.5 m Ah g-1 at a current density of 100 m A g-1 after 80 cycles,and after each 10 cycles at 100,200,500,1000,2000,5000 and 100 m A g-1,the specific capacities of the composites are about 840,723,511,402,336,224 and 703 m Ah g-1,respectively.The improved electrochemical performance of the composites is closely related to its sandwiched structure,which multicomponent Cu2O-Cu O nanospheres adhered tightly to both sides of RGO nanosheets.This could shorten the transport pathway for both electrons and lithium ions,prevent RGO nanosheets from stacking,enhance the electrical conductivity and accommodate the volume expansion during prolonged cycling.?2?Ultrathin CoO-Co₃O₄ nanoribbons were successfully sandwiched between reduced graphene oxide?RGO?nanosheets through a facile solvothermal method,which used directly as the anode material for lithium ion batteries.The as-prepared ultrathin CoO-Co₃O₄ nanoribbon/RGO sandwich-like nanostructures?CoO-Co₃O₄-RGO?delivers a reversible capacity of 994 m Ah g-1 at a current density of 100 m A g-1 after 200 cycles.Even at a high charge-discharge rate of 1000 m A g-1,CoO-Co₃O₄-RGO still demonstrate a reversible capacity of 395 m Ah g-1 after 500 cycles.The rate capability of CoO-Co₃O₄-RGO evaluated by the ratio of capacity at 100,200,500,1000,2000,5000 and 100 m A g-1 after each 10 cycles was about 1210,1060,890,730,578,392 and 915 m Ah g-1,respectively.The greatly enhanced performances for CoO-Co₃O₄-RGO may be ascribed to the synergistic effects: The multicomponent hybridizing advantages;The mutual influence of both avoids the CoO-Co₃O₄ nanoribbons and RGO nanosheets aggregation;The two-dimensional?2D?nanoribbons with the short lithium ion diffusion and 2D RGO sheets as conductive network built an efficient three dimensional?3D?storage active material.?3?A similar approach is proposed to synthesizea Cu O-Co₃O₄-RGO composites,using the layer-by-layer assembly method in a water-ethanol mixture.The Cu O-Co₃O₄-RGO composites delivered a reversible capacity of 847 m Ah g-1 at a current density of 100 m A g-1 after 200 cycles,and after each 10 cycles at 100,200,500,1000,2000,5000 and 100 m A g-1,the specific capacities of the composites are about 927?823?702?594?446?291 and 765 m Ah g-1 m Ah g-1,respectively.The improved lithium storage performance of Cu OCo₃O₄-RGO mainly resulted from the synergistic effects of multicomponent Cu O-Co₃O₄ nanospheres and RGO nanosheets.Cu O-Co₃O₄ nanospheres supported on RGO nanosheets formed a sandwiched structure and prevented RGO nanosheets from stacking.The RGO nanosheets impeded the volume dilatation of Cu O-Co₃O₄ nanospheres as effective 3D conductive networks after the charge-discharge processes.In a conclusion,The multicomponent metal oxide compounds were successfully sandwiched between reduced graphene oxide?RGO?nanosheets through a facile solvothermal method,which showed much higher reversible capacity,stable cycling performance and better rate capability.Through further research of its mechanism and further improvement of its preparation technology,heterostructured ternary metal oxides-reduced graphene oxide composites were proved to be a promising anode material for lithium-ion batteries.