Controllable Preparation Transition Metal Suldides On Graphene Surface And Their Supercapacitor Performance

Supercapacitors are expected to become the next generation of new energy storage devices due to their desirable characteristics of high power density,fast charging and discharging rate,long cycle life,environment-friendly and so on.Electrode material plays a key role in the performance of supercapacitor.Metal sulfide has characteristics of high theoretical capacitance and good conductivity and graphene has long cycle stability.The Ni₃S₂/graphene and binary metal sulfides/graphene composites was successfully prepared in this thesis.The effects of process parameters on the structure and electrochemical performance of the composites were studied.The relationship between the structure and performance of the composites was analyzed.NF@rGO/Ni₃S₂ composites with three-dimensional structure were successfully synthesized through one-step solvothermal method.Encouragingly,the as-synthesized composites exhibited excellent three-dimensional structure,in which the Ni₃S₂ nanoplates are uniformly distributed on the surface of graphene.Based on the above excellent microstructure,NF@rGO/Ni₃S₂ composites exhibited high specific capacitance of 4048 mF·cm-2?816.8 F·g-1?at the current density of 5 mA·cm-2?0.98 A·g-1?,which is far higer than the pure Ni₃S₂ of 2335 mF·cm-2.In addition,86.5% of the initial specific capacitance cauld be retained after 6000 cycles.At the same time,the effects of reaction temperature and solvent ratio on the microstructure and electrochemical performance of NF@rGO/Ni₃S₂ composites were analyzed.When the reaction temperature was 160 °C,the ratio of water and ethylene glycol was 1:1,the electrochemical performance of the composite was the best.An aqueous asymmetric supercapacitor was successfully designed using the NF@rGO/Ni₃S₂ as the positive electrode and the Nitrogen-doped graphene?N-G?as the negative electrode?denoted as NF@rGO/Ni₃S₂//N-G?.The NF@rGO/Ni₃S₂//N-G asymmetric supercapacitor exhibits high power density and energy density of 32.6 Wh·kg-1 and 399.8 W·kg-1,respectively.A facile two-step method was developed to improve the above process.First,the three-dimensional graphene substrate?NF@rGO?was prepared,and then the Ni₃S₂ nanoparticles were deposited on the substrate surface by liquid precipitation method.This novel method can realize controllable preparation of the growth of Ni₃S₂ particles on graphene substrate by reasonably adjusting the loading mass of graphene and Ni₃S₂ particles,which can give full play to the potential of the two materials.Detailed electrochemical measurements showed that the NF@rGO/Ni₃S₂ composite electrode exhibited high specific capacitance of 1140.7 F·g-1 at a current density of 1 A·g-1.Binary metal sulfide composites of NF@rGO/Ni₃S₂/Co₉S₈ was further fabricated using the same process parameters.The performance of NF@rGO/Ni₃S₂/Co₉S₈ is significantly increased compared with NF@rGO/Ni₃S₂,which can be attributed to the synergistic effect of composites.The as-prepared NF@rGO/Ni₃S₂/Co₉S₈//N-G deliver a high energy density of 49.6 Wh·kg-1 at a power density of 424.8 W·kg-1.