Study On Crystal Phase Control Of Cobalt-based Selenide And Supercapacitor Performance Of Composite Materials

Recently,transition metal selenium compounds have attracted wide attention in the field of energy storage due to their polymorphic characteristics and unique electronic structure.This article introduces the phase change engineering of transition metal cobalt selenide nanomaterials,the synthesis path and reaction temperature control the crystal phase structure of transition metal cobalt selenide nanomaterials,and explores the influence of crystal phase changes on electrochemical performance.Two different dimensional carbon materials were selected,the addition ratio of carbon materials was adjusted and combined with cobalt selenide to prepare cobalt selenide nanocomposites with different proportions,which achieved synergistic effects on multiple scales,thereby obtaining high-performance supercapacitor electrode materials.The main research contents of this paper are as follows:（1）The orthorhombic phase o-CoSe₂ and cubic phase c-CoSe₂ were synthesized through two selenization pathways:hydrothermal method and chemical vapor reaction.Study the influence of the synthesis route on the morphology,ion valence and energy storage performance of CoSe₂.Compared with o-CoSe₂,c-CoSe₂ has stronger electron transfer ability.At 1 A g^-1,the specific capacity of c-CoSe₂(295.5 m Ah g^-1)is higher than that of o-CoSe₂(204.3 m Ah g^-1).The energy density of the c-CoSe₂//AC device shows 71 Wh kg^-1 at a power density of 845 W kg^-1.The o-CoSe₂//AC device exhibits an energy density of 60 Wh kg^-1 at a power density of 850 W kg^-1.（2）Adjust the crystal structure of cobalt selenide by changing the annealing temperature of the chemical vapor reaction process.When the temperature increased from 600°C to 700°C,the transformation from cubic phase CoSe₂ to hexagonal phase Co_0.85Se was realized.At a current density of 1 A g^-1,Co_0.85Se-700 shows a specific capacity of 410.4 m Ah g^-1.The asymmetric supercapacitor based on Co_0.85Se-700//AC delivers a high energy density of 77.4 Wh kg^-1 at a power density of 856.3 W kg^-1.At a current density of 20 A g^-1,the Co_0.85Se-700//AC device still has a capacity retention rate of 82.4%after 10,000 cycles of testing.（3）A two-step hydrothermal method was used to synthesize CoSe₂,and on this basis,carbon-based materials with different mass ratios were added to successfully prepare CoSe₂/CNTs@C₃N₄ multi-scale nanocomposites.The CoSe₂/CNTs@C₃N₄-3nanocomposite shows a specific capacitance of 445.4 m Ah g^-1 at a current density of 1A g^-1.At a current density of 1 A g^-1,the mass specific capacitance of the assembled CoSe₂/CNTs@C₃N₄-3//AC device shows 191 F g^-1.The long-cycle test was performed when the current density was 10 A g^-1.After 5,000 cycles,the capacitance retention rate still exhibits 70%,which has excellent cycle stability.