Preparation And Energy Storage Performance Of Cobalt-Based Selenide Material

Along with the rapid development of technology and industrialization of human society and aggravation of environmental degradation and energy shortage,researchers pay more attention to efficient and green energy storage devices.Supercapacitors（SCs）are considered promising electrochemical energy storage devices due to their high power density,fast charging and discharging rate,long cycling life and good safety.Designing and developing novel electrode materials with high specific capacitance and stability is one of the effective ways to obtain high-performance supercapacitors.In recent years,transition metal chalcogenides have drawn a lot of attention from researchers due to their good conductivity,high theoretical capacity and low cost.Compared with oxygen and sulfur,selenium has a lower electronegativity and higher conductivity(1×10^-3 S m^-1).Therefore,the chemical bonds between selenides are weaker and the electronic states are more easily transformed,resulting in a higher electrochemical activity.However,the low specific capacitance and energy density of selenide-based supercapacitors,the poor cycling stability and rate capability,and the tedious and complicated preparation method limit their application in the field of energy storage.In this paper,cobalt-based selenides are studied from the perspectives of controlling morphology and phase structure,constructing composite material and exploring novel preparation processes to explore the preparation process and mechanism of high-performance cobalt-based selenide electrode materials,and then constructing asymmetric supercapacitors with graphene materials to explore their practical applications.The main research contents and conlusions are as follows:（1）The CoSe₂@NC/Gr composite electrode material with a multi-level pore structure was prepared by high-temperature annealing selenization in an inert atmosphere derived from Co-MOF.And the effects of different graphene additions on the morphological structure and properties of the material were further explored.The results show that the addition of graphene increases the number of micropores and mesopores in the composite electrode material,reduces the charge transfer resistance and ion diffusion resistance,and increases the specific surface area of CoSe₂@NC material.The as-synthesized CoSe₂@NC/Gr electrode with 10%mass addition of graphene exhibits the best electrochemical performance.It shows a specific capacitance of 430.4 F g^-1 at 1 A g^-1 and capacity retention of 66%as the current density increases to 20 A g^-1.After 3000 cycles at 5 A g^-1,it maintains 94.4%of its initial capacity,demonstrating good cycling stability.（2）The CoSe₂@N-C electrode material was synthesized by microwave selenization derived from Co-MOF,and the effects of different mass ratios of Co-MOF/Se on the morphological structure and properties of the material were further investigated.Structural characterization shows that the as-synthesized CoSe₂@N-C electrode with the mass ratio of Co-MOF/Se powder=1:1 shows a stable morphology and multiple phase structures（orthorhombic and cubic phases）,and when the mass of Se powder is further increased,the morphology of the sample collapses and only a single cubic phase structure is observed.Electrochemical tests show that the CoSe₂@N-C electrode material with a Co-MOF/Se mass ratio of 1:1 exhibits the best electrochemical performance,which can be attributed to its stable morphological structure and the synergistic effect of multiphase structure.（3）The effects of different microwave times on the morphological structure and properties of the electrode materials were further investigated with a Co-MOF/Se mass ratio of 1:1.The structural characterization shows that all samples prepared at different microwave times are composed of orthorhombic and cubic phases.Compared with the Co-MOF,CoSe₂@N-C exhibits a mesoporous structure and CoSe₂ is encapsulated in the nitrogen-doped carbon material.Electrochemical tests illustrate that the as-synthesized CoSe₂@N-C-2min electrode shows the best electrochemical performance with a specific capacitance of 395.7 F g^-1 at 1 A g^-1 and capacity retention of 63.5%as the current density increases to 20 A g^-1.After 5000 cycles at 5 A g^-1,it maintains 96.8%of its initial capacity,demonstrating good cycling stability.Further,the asymmetric supercapacitor was constructed with CoSe₂@N-C and GA materials as positive and negative electrodes,which has an energy density of 42.2 Wh kg^-1 at a power density of791.6 W kg^-1 and a capacity retention rate of 94.4%at 5 A g^-1 for 5000 cycles,demonstrating a great potential application for the CoSe₂@N-C electrode in the energy storage field.