Synthesis Of Transition Metal Sulfide-based Composite Materials For Electrochemical Capacitors Application

As an energy storage device with high-power density,electrochemical capacitors?ECs?have the advantages of fast charging-discharging rates and long cycling life.They are expected to efficiently store and transform renewable clean energy,thereby alleviating the fossil fuel crisis and environmental pollution problems.However,compared with battery systems,the lower energy density of ECs can't meet the needs of practical applications.As an important part of ECs,electrode materials play a decisive role in the overall performance of the device.Among various materials,transition metal sulfides based on nanoscale have been widely applied and developed in the field of energy storage due to their abundant reserves,low cost,high theoretical capacity and excellent chemical reactivity.Unfortunately,transition metal sulfides have lower electrical conductivity and poor mechanical stability than carbon materials,which limits their practical applications.Therefore,this dissertation focuses on the study of composite materials based on transition metal sulfides to improve electrochemical performances of electrode materials by regulating the morphology,structure and interface properties of them.In addition,based on the differences in energy storage mechanisms of different materials,asymmetric capacitors?ASCs?devices are constructed to broaden the potential window of ECs,increasing the energy density of the device.The main research works of this dissertation are as follows:1.NiCo2S₄ nanosheets were successfully synthesized by the hydrothermal and ion exchange method with DNA molecules as templates.The introduction of the cross-linked network structure and basic elements?C,N,P?of DNA molecules enhanced the conductivity and reactivity of the electrode material.By adjusting the concentration of the DNA solution,the NiCo2S₄ nano-electrode material with the best electrochemical performance was obtained.This electrode exhibited a specific capacity of 644 C g-1 at the current density of 1 A g-1,and the capacity retention of 90.5%after 1500 cycles.2.The three-dimensional MnS/Co9S8 micro-flowers composites with serrate edges on Ni foam substrate were successfully prepared by a two-step hydrothermal method.The serrate edge structure can increase the contact area between electrode material and the electrolyte,which can enrich active sites for electrochemical reactions.By optimizing the dosage of the structure-directing agent?NH4F?and time-varying experiments,the electrode material with the best electrochemical performance was selected.This battery-type electrode material and activated carbon?AC?were assembled into the MnS/Co9Ss//AC-ASCs device,which exhibited energy density of 34.1 Wh kg-1.3.We took advantage of glutamine?Gln?as building block to synthesize N site activated cobalt sulfide@N,S dual-doped carbon composite materials?CS@NSC?through chemical precipitation and chemical vapor deposition methods.Based on the coordination reaction of amino and carboxyl functional groups in Gln with metal ions,heteroatoms can be in-situ introduced into the composite material of carbon substrate and cobalt sulfide,which can improve the activity of the redox reaction.By adjusting the molar ratio of Gln and Co,the CS@NSC as a battery-type electrode material with optimal electrochemical performance was obtained.In addition,the strategy of in-situ doping heteroatoms into a composite material was also suitable for synthesizing N site activated nickel sulfide@N,S dual-doped carbon composites.Furthermore,the constructed CS@NSC//AC-ASCs device exhibited a high energy density of 67.8 Wh kg-1.