Design,preparation And Electrochemical Characterization Of Transition Metal Sulfides Electrodes For Supercapacitor Applications

Supercapacitors have promising applications in portable electronic devices,hybrid-electric vehicles and smart power grides owing to the advantages of long cycle life,high power density,short charge time,safe reliability and wide working temperature range.Electrochemical properties of supercapacitors are intensely related to electrode materials and structures.Transition metal sulfides?TMS?have been paid much attention due to their high theoretical capacitance and reversible redox properties.This thesis mainly concentrates on the synthesis of TMS and the improvement of electrochemical performance through recombination TMS with good conductive carbon materials.The main research contents are as follows:?1?A two-step electrochemical treatment is carried out to prepare functionalized exfoliated graphite?FEG?,using?400?m graphite foil?G?as start materials.One step method as-synthesized graphite foil is denoted as exfoliated graphite?EG?.Self-supported electrode of FEG-Ni₃S₂/Ni₃S₄ is synthesized by hydrothermal method.The experimental results indicate that,comparing to G and EG,FEG substrate has substantial improvement in hydrophilic property and conductivity.The surface of FEG substrate is covered with plentiful exfoliated graphene nanosheets which accelerate the transmission of electrons and reduce the internal resistance.FEG-Ni₃S₂/Ni₃S₄ delivers an area capacitance of?883.5 mF cm^–22 at 2 mA cm^–2,much larger than EG-Ni₃S₂/Ni₃S₄(?571.5 mA cm^–2)and G-Ni₃S₂/Ni₃S₄(?138.1 mF cm^–2).?2?In order to futher improve the electrochemical performance of TMS,we prepare the interconnected hollow carbon shells,and then produce an electrode architecture?C@Mo S₂/Ni₃S₄?on the carbon shells by hydrothermal method.Electrochemical measurements indicate that the C@MoS₂/Ni₃S₄ structure has excellent supercapacitive properties especially for long term cycling at high current densities.The improved performance of C@MoS₂/Ni₃S₄ can be attributed to the reduced equivalent series resistance by interconnected C shells and the enhanced cycling stability by MoS₂.The relatively dispersedly distributed nanosheet-shaped MoS₂/Ni₃S₄ provides efficient contact with electrolyte and effectively buffers the volume change during charge/discharge processes.A specific capacitance as high as?640.7 F g^–1 can still be delivered even after 10000cycles at a high current density of 20 A g^–1.