Synthesis Of Metal Oxide/graphene Composite Materials And Research Its Lithium Storage Performance

Lithium ion batteries?LIBs?have been widely utilized in the field of mobile phones,laptops,cameras,and other portable electronic devices owing to their advantages of high open circuit voltage,high energy density,long cycle life,environmental friendliness,and small self-discharge.Now,the commercial graphite anode with a low theoretical capacity of 372 m A h g-1 can not meet the growing demands for high energy consuming applications,such as the pure electric vehicles,hybrid electric vehicles,and other new energy vehicles.Recently,metal oxides have been widely investigated as alternative anode materials for high-performance LIBs due to their high theoretical capacity.However,the metal oxides anodes usually exhibited poor rate performance and short cycle life due to the huge volume expansion/contraction?³00%?during cycling.Thus,graphene was introduced to the materials,which combines with metals oxides to improve the electrochemical performances of the materials.The as-made composite materials exhibited excellent electrochemical performances.In this paper,we successfully synthesized SnO₂/graphene and MnO₂/graphene hybrid materials.The microstructure and morphology of SnO₂/graphene and MnO₂/graphene were characterized in detail by means of SEM and TEM etc.Then,we explore the electrochemical performance of the SnO₂/graphene and MnO₂/graphene.This article contains the following sections:1.We successfully synthesized the SnO₂/graphene composite materials through a facile hydrothermal reaction.The TEM images show that SnO₂ nanocrystals are homogeneously distributed on the RGO nanosheets surface,and the size of SnO₂ nanocrystals is around 4-5nm in diameter.The composite materials exhibite excellent lithium storage performance.The as-made SnO₂/graphene composite materials show a reversible capacity as high as 1165.5 mA h g-1 after 80 cycles under a current density of 200 mA g-1,which is about 98.2% capacity retention compared with that in the second cycle.Even under 500 mA g-1 high current density,the remaining capacity is 660.8 mA h g-1 after 300 cycles.The high reversible capacity can be attributed to the introduction of graphene.In addition,we further investigate the reaction mechanisms of the composites materials as an anode material for LIBs.2.Firstly,we prepared carbon spheres using glucose as a carbon precursor byhydrothermal method.Subsequently,potassium permanganate reacting with the carbon spheres generates layered MnO₂ on the surface of carbon spheres.Finally,MnO₂/graphene composite materials were generated by coating graphene.At current density of 100 mA g-1,the composites materials electrode exhibited a reversible capacity as high as 806.4 mA h g-1after 150 cycles.Even under high current density of 500 mA g-1,a reversible capacity of 664.3m A h g-1 after 200 cycles was achieved.Excellent cycle performance is highly related to the present of graphene.The graphene with high surface area not only can restrain the volume effect,but also can enhance the conductivity of the electrode,thereby improving the electrochemical properties of materials.3.Firstly,Mn₃O₄ octahedra were conveniently prepared through dealloying of an Mn/Al alloy in 2 mol/L NaOH solution at room temperature.Subsequently,the obtained Mn₃O₄ octahedra was modified with aminopropyltrimethoxysilane?APS?to render the Mn₃O₄ octahedra surface positively charged.Finally,the excellent graphene/APS-Mn₃O₄?G/A-Mn₃O₄?composites materials were achieved by coating graphene.The as-made G/A-Mn₃O₄ composite materials show a reversible capacity as high as 967.5 mA h g-1 after100 cycles under a current density of 200 mA g-1,which is almost three times as high as the value of pure Mn₃O₄ octahedra.Even under high current density of 1000 mA g-1,a reversible capacity of 604.4 mA h g-1 after 200 cycles was achieved,indicating that the introduction of graphene vastly improve the electrochemical properties of the Mn₃O₄ octahedra.