Preparation And Supercapacitive Performance Of Nickel-based Composites

Supercapacitors have attracted considerable attention owing to their inherent merits of high Coulomb efficiency,excellent charge and discharge efficiency,wide operating temperature range,and outstanding power output.As an important part of supercapacitors,electrode materials play a vital role in the performance of supercapacitors.Therefore,the exploration of electrode materials with excellent performance is the most important part of the research work of supercapacitors.Nickel-based materials have the advantages of relatively high specific capacities,low preparation cost,and environmentally friendly,and have been demonstrated to be promising electrodes for supercapacitors.In this paper,a series of nickel-based composite materials with specific structures have been prepared,such as nitrogen-doped carbon dots(NCDs)decorated Co doped Ni S flower-like hierarchitectures,NCDs and Co₃O₄modified Ni₂P flower-like structure,and ultra-thin two-dimensional carbon nanosheets(CNS)supported Ni₃S₂/Co₉S₈nanoparticles.The electrochemical properties of the prepared nickel-based composite materials were systematically studied.In addition,coupling with a p-phenylenediamine(PPD)modified reduced graphene oxide(r GO)anode,various hybrid supercapacitor devices were successfully constructed.The main research contents are as follows:1.An effective two-step solvothermal route was demonstrated to synthesize NCDs decorated Co-doped Ni S(Co-Ni S)flower-like hierarchitectures.Because of the modification with NCDs and doping by Co atoms,the resulting Co-Ni S/NCDs hierarchitectures depict an ultrahigh specific capacity up to 1240 C g^-1(2480 F g^-1)at1 A g^-1and a remarkable rate capability of 790.8 C g^-1(1581.6 F g^-1)even at 20 A g^-1when used as advanced electrodes for supercapacitors.More significantly,coupling with a PPD/r GO anode,a hybrid supercapacitor device was successfully constructed,which possesses an impressive energy density of 71.6 Wh kg^-1at 712.0 W kg^-1and a decent cyclic stability of 78.3%retention after 12000 cycles at 5 A g^-1.The dual improvement strategy may provide insight to rational engineer novel electrode materials with multi-components for high-performance hybrid supercapacitors.2.Two-step hydrothermal and phosphorization method was demonstrated to optimize the electrochemical performance of Ni(OH)₂nanosheets by using NCDs as the structural directing agent for the assembly of functional nanomaterials.NCDs modified Ni(OH)₂flower-like structure was firstly prepared by hydrothermal method,and then Co₃O₄nanoparticles were successfully grown on the surface of Ni(OH)₂by the second hydrothermal strategy.After phosphate treatment,the flower-like structure was maintained,and Ni₂P deposited with NCDs and Co₃O₄ternary composites were obtained.The as-prepared Ni₂P/Co₃O₄/NCDs flower-like structure possesses an ultra-high electrochemical capacity of 1044 C g^-1at 1 A g^-1.Moreover,a hybrid supercapacitor assembled by Ni₂P/Co₃O₄/NCDs and PPD/r GO electrodes has a maximum energy density of 53.5 Wh kg^-1at 772.9 W kg^-1,which has a broad prospect in the field of hybrid supercapacitors.3.Using metal oleates as raw materials and Na₂SO₄as template,Ni₃S₂/Co₉S₈nanoparticles supported on two-dimensional ultra-thin carbon nanosheets(CNS)were prepared by one-step calcination strategy.The prepared composites have ultrathin stacked sheet structure,which can provide a large number of active sites and endow the composites excellent electrochemical properties.Ni₃S₂/Co₉S₈/CNS composites possess an ultra-high electrochemical capacity of 1160 C g^-1(2320 F g^-1)at 1 A g^-1.At a high current density of 10 A g^-1,the capacity retention rate of Ni₃S₂/Co₉S₈/CNS is about 91.3%after 10000 charge/discharge cycles.The constructed Ni₃S₂/Co₉S₈/CNS//PPD/r GO hybrid supercapacitor device exhibits a maximum energy density of 69.6 Wh kg^-1and excellent cycle stability.The retention rate reaches 82.6%after 20000 cycles.Therefore,the fabricated Ni₃S₂/Co₉S₈/CNS ultra-thin nanosheets display great application prospect in the field of energy storage.