Graphene And Graphene Ternary Composites As Anode Materials For Lithium-ion Batteries

Graphene is a two-dimensional hexagonal honeycomb lattice material that consists of sp2 hybridized carbon atoms and has the thickness of only one carbon atom.Due to its excellent physical and chemical properties,it has been studied by many researchers.Few-layer graphene is prepared by organic synthesis in this paper.The prepared graphene is tested by some characterization means and studied as the anode of lithium ion batteries.Lithium-ion batteries,as the important new energy,possess many advantages such as high safety,long cycle life,high energy,high voltage,small self-discharge rate and no memory effect,etc.The graphene oxide prepared by Hummers method is combined with metallic oxide and nonmetallic oxide to produce the ternary composites of SnO₂-B₂O₃/graphene and SnO₂-MoO₂/graphene.The ternary composites are characterized by morphology and chemical structure and tested by electrochemical properties as the lithium ion battery anode.Graphene layer was synthesized at 95 °C by the Ullmann reaction using acetylene as the raw material.Hexabromobenzene?HBB?and cuprous bromide were used as the catalyst in this reaction.Moreover,the synthesized graphene layer used as the anode of lithium-ion battery exhibited the initial and reversible capacities of 650 and 570 mAh g-1,respectively,which were in accordance with the theoretical capacity of graphene.SnO₂-B₂O₃/graphene?SnO₂-B₂O₃/G?composite are fabricated by a hydrothermal-reflux method.The ternary composite is produced using graphene oxide,SnCl2·2H2O and boric acid as raw materials at 85 °C.The added B₂O₃ dramatically improves the electrochemical performance of lithium ion batteries compared to the SnO₂/G composite.The SnO₂-B₂O₃/G composites as anode show an outstanding discharge capacity of 1404.9 mAh g-1 at 500 mA g-1 after 200 cycles and an excellent rate capacity,which apparently outperforms the previously reported SnO₂-based anode material.These improved electrochemical performance characteristics are due to the B₂O₃ playing a buffering role,which are easily beneficial for accommodating the volume change during the lithium ions insertion/extraction processes.Furthermore,boron atoms can accept electrons for its electron-deficient nature,and boron could release electrons thus the electrons density and conductivity was increased.SnO₂-MoO₂/graphene nanocomposite is prepared by the same reflux method.The reversible capacity of the material prepared under optimum conditions as anode still remain to 1154 mAh g-1 at 100 mA g-1 after 130 cycles,which is the 89.9% of the first charge capacity.Graphene has a high electrical conductivity to improve the conductivity of the composite material,as well as alleviates the volume change of metal oxide during charge and discharge;in addition,smaller particles of SnO₂ and MoO₂ offer a shorter transmission path for lithium ion and electrons.All those point makes the composite materials exhibit good electrochemical performance.Relative to the SnO₂/graphene,the introduced MoO₂ improve the electrochemical performance to a certain degree.