Preparation Of Transition Metal Freestanding Electrodes And Their Performance Of Supercapacitor

Supercapacitor is one of the most promising energy storage devices,which has a higher energy density and power density than conventional capacitor.As we all know,the development of electrode materials is one of the key factors to improve the performance of supercapacitor.Currently,commercial supercapacitor electrodes are mainly based on carbon-based materials.Compared with carbon materials,pseudocapacitor materials have higher specific capacitance.However,low rate performance and poor cyclic stability still are the main factors that constrain its development.In this paper,the composite electrodes were prepared by growing nickel cobalt-based transition metal oxide,sulfide,and hydroxide on three-dimensional carbon nanotube foam,which exerted the advantages of both carbon materials and pseudocapacitor materials.The prepared composite electrodes possess high gravimetric,area,volumetric capacitance,good rate performance and cycle stability,which provide a theoretical reference for the development of wearable hybrid supercapacitors.Results are as follows:?1?polyurethane?PU?sponge was used as a template to absorb SWNTs by means of infiltration.After drying the PU@SWNT was obtained.After burning on the alcohol burner,nitrogen-doped 3D elastic single-walled carbon nanotube sponge?NSCS?was prepared.NSCS has good elasticity and conductivity,light weight,and can be served as a flexible free-standing electrode substrate.The NiCo₂O₄@CNTs@NiCo₂O₄ nanosheets grew on the NSCS by two-step hydrothermal and two-step annealing treatments.The gravimetric specific capacitance of 2281 F g^-1 at the current density of 5 A g^-1.Furthermore,the electrode has good cycle stability,after 5000 charge/discharge cycles,the capacitance retention was 86%maintained.?2?NiCo₂O₄ nanosheet grew on NSCS by hydrothermal and annealing methods,and then the NiCo₂O₄ nanosheet were transformed into contractible NiS₂/NiCo₂S₄ nanosheet through a sulfurization process.After the sulfurization treatment,NSCS skeleton shrinks,and the volume shrinks to 1/10 of the previous volume?NiCo₂O₄/NSCS?,which greatly increases the areal capacitance and volumetric capacitance of the material,and provides a possibility for miniaturized portable equipment.The contractible NiS₂/NiCo₂S₄/NSCS exhibited ultrahigh gravimetric specific capacitance of 2905 F g^-1,areal capacitance of 10.46 F cm^-2 and volumetric capacitance of 1307.25 F cm^-3 at a current density of 1 A g^-1.In addition,the NiS₂/NiCo₂S₄/NSCS also achieved a good rate capability,after 10000 charge/discharge cycles at 10 A g^-1,the capacitance retention was 83%maintained.Furthermore,an asymmetric supercapacitor?ASC?was fabricated with positive electrode of NiS₂/NiCo₂S₄/NSCS and negative electrode of activated polyaniline-derived carbon?APDC?in 6M KOH electrolyte.It delivered high gravimetric energy density of 58.1 Wh Kg^-1 at 797.9 W Kg^-1.The ASC achieves a high capacitive retention of 80%after 20000 cycles at a current density of 5 A g^-1.?3?The nickel and cobalt layered double hydroxide?Ni-Co LDH?grew on NSCS by hydrothermal treatment,and then Ni-Mn LDH was coated on the above sample by chemical polymerization to obtained Ni-Co LDH@Ni-Mn LDH/NSCS electrode,which greatly improved the gravimetric specific capacitance of the electrode materials.The electrode exhibited ultrahigh gravimetric specific capacitance of 4370 F g^-1 at a current density of 1 A g^-1.Moreover,an asymmetric supercapacitor?ASC?was fabricated with positive electrode of Ni-Co LDH@Ni-Mn LDH/NSCS and negative electrode of APDC in 2 M KOH electrolyte.It delivered high gravimetric energy density of 64.2 Wh Kg^-1 at 802 W Kg^-1 and volumetric energy density of 52.3 W h L^-1 at 718W L^-1.