Construction,Doping And Supercapacitor Properties Of Transition Metal Oxide/Sulfide Composite With Three-dimensional Frame Structure

As a new type of energy storage equipment with high power density,long cycle life,excellent rate performance and fast charging and discharging,supercapacitor has wide application prospects in electric vehicles,portable electronic equipment,aerospace,military and other fields.But the lower energy density,low cycle stability and narrow operating voltage window restrict its commercialization.At present,the main ways to improve the energy density and cycle stability of supercapacitors are as follows:improving the specific capacitance of electrode materials through the reasonable construction of micro morphology and collaborative composite of multiple materials;widening the voltage window of supercapacitor devices.As the key component of supercapacitor,electrode material is very important to improve the overall performance of the device.Transition metal oxygen/sulfide has many advantages,such as large reserve,low toxicity,environmental protection,simple synthesis process,etc.When they are used as electrode materials for supercapacitors,they have the advantages of high theoretical specific capacitance,good conductivity and excellent electrochemical activity.They have been widely studied and applied in energy storage field.However,compared with carbon materials,the conductivity and structural stability of transition metal oxygen/sulfide are poor.Therefore,it has become one of the research hotspots to improve the specific capacitance of materials by controlling,constructing micro morphology and composite design of electrode materials,and to enhance the potential window by preparing asymmetric supercapacitor devices.Based on the previous research results of our Lab,combined with the latest development in energy storage,this paper mainly focuses on the following two aspects:the construction of composite electrode materials by designing and controling of the morphology and structure of the electrode materials,as well as optimizing and doping of transition metal compounds,to improve the electrochemical performance of composite electrode materials;the assembly of capacitors:through the asymmetric supercapacitor（ASC）devices are over assembled to increase the potential window,so as to improve the energy density.The following work is carried out in this paper:（1）Three dimensional template（3Dr GN）is constructed by using polystyrene（Ps）spheres as hard plate and intercalated reduced graphene oxide（RGO）.A sandwich like nanocomposite material（3Dr GN-Mn O₂-PANI）is prepared by two-step electropolymerization on the surface of the template.The structure can improve the porosity of the material and provide more channels for the diffusion and transmission of ions.The synergistic effect between the ternary materials makes the composite show excellent electrochemical performance.At the current density of 1 A g^﹣1,the specific capacitance of the composite is 1181F g^﹣1.The specific capacitance can be maintained to 89.1%after 1000 cycles and the electrochemical stability is good.The above results show that:the three-dimensional frame structure supported by Ps is helpful to prevent the aggregation of r GN,the sandwich like layer by layer composite structure provides a bridge for the charge transfer between the ternary substances.It also provides a larger specific surface area for the reaction,helps to promote the diffusion of electrolyte ions in the material,and improves the utilization rate of electrode materials.（2）Based on the doping metal strategy,the three-dimensional popcorn like Sn-Ni₃S₂ composite is prepared by two-step hydrothermal method with Sn-Ni-MOF as the precursor.Based on the metal doping strategy,Sn-Ni₃S₂ composite with three-dimensional popcorn like structure is prepared by two-step hydrothermal method using Sn doped Ni MOF（Sn-Ni-MOF）as precursor.The results show that when the doping concentration of Sn is 0.024 mmol,the composite electrode material（SNS-3）has the best electrochemical performance.The specific capacitance of SNS-3 is 1667 F g^﹣1 at the current density of 1A g^﹣1.After 5000 cycles,the specific capacitance can be maintained at 81.8%.The asymmetric supercapacitor（ASC）assembled by SNS-3 and AC（SNS-3//AC）exhibited high energy density of 29.1 Wh kg^﹣1.The above results are due to the coarser popcorn like structure and suitable metal doping,which can increase the specific surface area and provide more active sites for redox reaction.This work provides a new idea for the design and development of Sn Doped Nickel Based sulfide composite electrode materials.（3）On the basis of the research above,the Co,Zn and Cu with abundant and economical benefits are selected as the doped metals in the three-dimensional framework of Ni-MOF.The three-dimensional framework of Ni-MOF doped with different metals（M@Ni MOF）was prepared by solvothermal method.The different morphology of the products are prepared by further vulcanization with sulfur powder as the sulfur source by high temperature annealing M@Ni S_x.Co@Ni S_x has the maximum specific capacitance and good ratio performance.The specific capacitance is 1997 F g^﹣1at the current density of 1 A g^﹣1,and the specific capacitance retention can be maintained at 90.7%after 2000 cycles.（4）Co is selected as the doping metal to construct the three-dimensional metal frame structure of Co Ni MOF,The introduction of Co endows the Ni-MOF microspheres with unique core-shell structure,and forms nanosheets with high conductivity on the surface of the microspheres,and the bimetallic sulfide composite（CNS）was prepared by annealing at high temperature using Co Ni MOF as the precursor.The effect of different Co doping concentration on the structure and properties of electrode materials was investigated.It is determined that the best performance of the composite material CNS-2 is obtained when the concentration of doping Co is 5.0 mmol.Its unique three-dimensional core-shell porous microsphere structure composed of nanoparticles promotes the Faraday redox reaction and mass transfer performance of the material,and has excellent supercapacitor performance.The results showed that the specific capacitance can reach 1997 F g^﹣1 and retains 84.9%at 10 A g^﹣1.The constructed ASC device（CNS-2//AC）provided a wide voltage window of 1.7 V,and exhibited a high energy density of 65.6 Wh kg^﹣1 at the power density of 0.85 k W kg^﹣1.The specific capacitance can be maintained at 85.7%after 5000 cycles at the current density of 10A g^﹣1.Through the strategies above,effective structural design,construction and doping are carried out to form three-dimensional composite electrode materials with different morphologies,excellent specific capacitance and good cycle stability.The assembled supercapacitor devices also have high energy density.This research provides a new idea for improving the overall performance of supercapacitor.