Controlled Synthesis Of Nickel-based Selenides For Hybrid Supercapacitors

Supercapacitors,as a new type of energy storage device,have attracted widely attention due to their higher power density and longer cycle life than traditional rechargeable batteries.They are favorable for various applications that require fast charging and high-power output,such as hybrid electric vehicles,large industrial equipment and portable electronics.However,their applications are limited due to the lower energy density.Supercapacitors with high energy density require the electrode materials that integrate high specific capacity and wide operating voltage window.Compared with oxygen and sulfur,selenium has relatively higher conductivity and higher metallicity,which makes transition metal selenides become important energy storage materials and have potential application prospects for hybrid supercapacitors.Herein,the research object mainly focuses on the structural design,morphology control and performance optimization of the nickel selenide nanomaterials.Besides,we have also explored the influence of synthesis conditions on the composition,morphology,and electrochemical performance of as-prepared nanomaterials.Finally,a high-performance supercapacitor device is obtained by assembling a hybrid supercapacitor.The main research contents of this paper can be summarized as follows:（1）By adjusting the hydrothermal reaction conditions,we have prepared Ni Se,Ni_0.85Se and Ni Se-Ni_0.85Se nanomaterials,and measured their electrochemical performance.The composition structures and morphologies of as-prepared active materials are measured by XRD,SEM,TEM,XPS characterization.Moreover,the results show that Ni Se-Ni_0.85Se composite exhibits the best electrochemical performance.The Ni Se-Ni_0.85Se electrode shows a high specific capacity of 669 C g^-1.When the current density is increased to 20 A g^-1,it can maintain a high specific capacity of 460 C g^-1（69%）and good cycling performance.Finally,we have assembled a Ni Se-Ni_0.85Se//r GO hybrid supercapacitor,which shows a high energy density of 41 Wh kg^-1and good cycling stability（80%capacity retention after 5000 cycles）,indicating its potential in practical application.（2）Ni Se₂ and Ni Se₂@r GO nanomaterials are prepared by hydrothermal method.SEM and TEM characterizations reveal that the r GO nanosheets-wrapped Ni Se₂nanocomposites reduce particle aggregation,and the Ni Se₂@r GO nanocomposite has a larger specific surface area and better conductivity than pure octahedral crystal of Ni Se₂.Compared with Ni Se₂ electrode,the Ni Se₂@r GO electrode exhibits better electrochemical performance with a high specific capacity of 467 C g^-1(1 A g^-1)as well as good rate capability(340 C g^-1 at 20 A g^-1,～73%capacity retention).Moreover,we have also constructed a hybrid supercapacitor using the r GO as the negative electrode and Ni Se₂@r GO as the positive electrode,which shows a high energy density of 34.29Wh kg^-1 along with excellent cycle stability(93%capacitor retention after 5000 cycles at 10 A g^-1),demonstrating its viability and potential for practical applications.