Microwave Hydrothermal Synthesis Of Graphene-based Composites And Their Applications In Energy Storage Device

With the increasing depletion of traditional fossil energy and a series of problems caused by environmental pollution,the development and utilization of new energy sources（wind,solar,etc.）has become urgent.However,these renewable energy sources are territorial,intermittent and volatile,therefore energy storage devices that can meet the requirements of high power density/energy density and excellent cycle performance are needed to improve the utilization of renewable energy.In this paper,Co₃O₄/reduced graphene oxide（r GO）,Co Se₂/r GO and Fe Se₂/r GO nanocomposites were prepared by a simple and efficient microwave hydrothermal method and used as electrode materials for energy storage devices.The details of this paper are as follows:（1）Co₃O₄/r GO nanocomposites with three-dimensional hierarchical structure were prepared by a one-step microwave hydrothermal method and their electrochemical properties as supercapacitor electrodes were investigated.Thanks to the synergistic effect between Co₃O₄ and r GO,the prepared Co₃O₄/r GO composite shows a high specific capacitance of1031 F g^-1 at 1 A g^-1 and excellent rate performance,and its specific capacity is still maintained at 800 F g^-1 at a current density of 10 A g^-1 with a capacity retention rate of 78%.In addition,after 8,000 cycles at a current density of 1 A g^-1,the capacity is still maintained at 88%.（2）Co Se₂/r GO nanocomposites with C-Co bond coupling were prepared by a simple and efficient microwave hydrothermal method,and the electrochemical properties of Co Se₂/r GO nanocomposites with different r GO contents were systematically compared when used as the anode of sodium ion batteries.The prepared Co Se₂/r GO composites with the optimal r GO content showed a high reversible capacity of 416 m Ah g^-1 after 200 cycles at a current density of 0.5 A g^-1.And when the current density was increased from 0.5 A g^-1to 20 A g^-1,Co Se₂/r GO showed good multiplicative performance with the discharge capacity varying from 533 m Ah g^-1 to 420 m Ah g^-1.and still showed a high discharge capacity of 402m Ah g^-1 after 850 cycles at a high current density of 5 A g^-1.（3）Fe Se₂/r GO nanocomposites with C-Fe bond coupling were prepared by a simple and rapid microwave hydrothermal method and used as sodium ion battery anodes.The characterization and electrochemical kinetic analysis showed that the Fe Se₂/r GO composites have fast sodium ion diffusion ability and high pseudocapacitance contribution.It shows a high reversible capacity of 451 m Ah g^-1 after 80 cycles at 0.2 A g^-1 and maintains a high capacity of 185 m Ah g^-1 at 10 A g^-1.In addition,excellent cycling capability was also demonstrated,showing a reversible capacity of 401 m Ah g^-1 even after 2200 cycles at 1 A g^-1.