Design And Fabrication Of Supercapacitor Devices Based On Hierarchical Zn-Co Bimetallic Selenides

With the high-speed development of electric vehicles and portable electronics,advanced energy-storage devices with excellent energy density and high power performance have received considerable interests.Hybrid supercapacitors（HSCs）have become a hot topic for scientists due to their high power and high energy performance.However,due to the relatively low energy density of the electrode,its practical application is limited.Therefore,high performance electroactive materials are still urgently needed.Among the various electrode materials used in HSCs devices,bimetallic selenides have higher power due to the synergistic effect between different metal ions and higher electrical conductivity(1 × 10^-3S m^-1)are better candidates for electrode materials for HSC devices.On the one hand,the morphology of electroactive materials can greatly affect the electrochemical performance,hierarchical structures are always favorable for improving energy and power density,as well as cycling stability of electroactive materials because of their large surface area,enhanced electron and ion diffusion,easily accessed storage sites and long durability.On the other hand,composition is another key factor affecting the properties of electroactive materials,so it is necessary to explore the relationship between the ratio of metal ions and the electrochemical properties of electrode materials.The main contents of the experiment include the following two parts:（1）Zn Se&CoSe₂（ZCS）,Zn Co₂O₄（ZCO）,CoSe₂,and Zn Se with 3D hierarchical sea urchin morphology were synthesized by low temperature selenation.ZCS showed excellent specific capacity,which significantly better than the Contrast material, for example:high specific capacity(1419 C g^-1@2 A g^-1),excellent rate performance(capacity retention rate is 81.7%@20 A g^-1),excellent cycle stability （88.3%@5000 times cycle）.The excellent electrochemical performance of ZCS is attributed to the hierarchical structure allowing rapid diffusion of electrolyte ions; buffering volume changes that occur during charging/discharging;a stable interconnected conductive network with a shortened charge transfer path and lower charge transfer resistance.In addition,ZCS//Activated Carbon（AC）HSCs devices also exhibit excellent performance,such as energy density up to 77.78 Wh kg^-1@0.222 kW kg^-1power density and 44.44 Wh kg^-1@2.22 kW kg^-1, Excellent cycle stability（80%capacitance retention rate@10000 cycles）,which is at the leading level of similar materials. （2）A series of Zn-Co selenides(Zn Se,Zn_0.75Co_0.25Se,Zn_0.67Co_0.33Se,Zn_0.5Co_0.5Se, Zn_0.5Co_0.5Se,Zn_0.33Co_0.67Se,CoSe₂)with 3D hierarchical flower-like overall morphology were prepared.Zn_0.67Co_0.33Se exhibits excellent specific capacity, which is significantly better than the control material,such as high specific capacity(1107 C g^-1@1 A g^-1),excellent rate performance(capacity retention rate 84%@10 A g^-1),excellent cycle stability（80.2%@2000 cycles）.The excellent electrochemical performance of Zn_0.67Co_0.33Se benefits from the hierarchical structure and synergistic effect of precise regulation.In addition,Zn_0.67Co_0.33Se//AC hybrid supercapacitors also exhibit excellent performance, such as energy density up to 66.2 Wh kg^-1@0.208 kW kg^-1power density and 58.1 Wh kg^-1@2.08 kW kg^-1,excellent cycle stability（97%capacitance retention rate@10000 cycles）,which is at the leading level of similar materials.