Preparation Of High Specific Energy NiCo₂O₄ Composite Electrode And Its Performance As Supercapacitor

Supercapacitors,also known as electrochemical capacitors,are novel power storage device between tradition capacitors and secondary batteries.Supercapacitors have significant potential,including high power density,long cycle life,fast charge/discharge rates,and easy maintenance.Supercapacitors have been extensively used in civilian,military,aerospace,traffic and transportation areas because of their distinctive electrical properties.The trasition medal oxides have wonderful specific capacicitance than carbon materials,but always suffer from some weakness,like low electrical conductivity,volume shrinkage duing the charge-discharge process,poor cycle life.In this paper,we conbine NiCo₂O₄ with novel two-dimensional graphene film and three-dimensional carbon foams,developing three different free-standing and flexible electrodes,making great progress in specific capacitance and cycling stability.The paper provides a favorable theoretical and scientific basis for developing high performance asymmetric supercapacitors.The details are as follows:?1?Two-dimensional graphene and one-dimensional carbon nanotubes were used to fabricate layered film.The carbon nanotubes were inserted into the graphene sheets to suppress the stacking effect of graphene.The flexible films were formed by mixture carbon nanotube and graphene by vacuum suction.For better enhance the capacitance electrochemical performance,a novel hierarchical structure free-standing and binder free electrode of corrugated NiCo₂O₄ nanosheets on nitrogen doped graphene/carbon nanotube?NGN/CNTs?film has been designed for high-performance supercapacitor.The unique structure with light weight electrode achieved super high electrochemical performance with volumetric capacitance of 482.7 F cm^-3,gravimetric capacitance of 2292.7 F g^-1 at 5 A g^-1 and super long-term cycle stability(125% capacitance retention,after 10000 circles at 30 A g^-1).An optimal supercapacitive performance also achieved in our fabricating asymmetric supercapacitor?ASC?by using NiCo₂O₄/NGN/CNTs as cathode and NGN/CNTs as anode.The device exhibited high gravimetric energy density of 42.71 W h kg^-1 at 775 W kg^-1,24.69 W h kg^-1 at high gravimetric power density of 15485 W kg^-1,even a high volumetric energy density of 25.90 W h L^-1 and high volumetric power density of 9389 W L^-1.A 86% of capacitance retention was maintain after 10000 circles.?2?A novel nitrogen-doped carbon nanotubes?CNTs?Sponge?NSCS?with a 3D interconnected network has been successfully fabricated by pyrolyzing commercial polyurethane?PU?sponge coated with SWNTs,showing excellent elasticity and ultra light-weight.Moreover,advanced electrode of the NiCo₂O₄ nanosheet supported on NSCS has been successfully fabricated through hydrothermal method combined with annealing treatment.Benefiting from the compositional features and 3-D structures,NiCo₂O₄/NSCS electrode exhibits high rate capability and excellent cycling stability with high gravimetric capactiance of 1618 F g^-1 in low density of 0.52 g cm^-3 and high volumetric capacitance of 790 F cm^-3 in high mass density of 1.43 g cm^-3.Moreover,a high performance asymmetric supercapacitor was successfully fabricated by using NiCo₂O₄/NSCS as positive electrode and NGN/CNTs film as negative electrode,exhibiting high gravimetric energy density of 46.01 Wh kg^-1 at 800.15 W kg^-1 and volumetric energy density of 32.29 Wh L^-1 at 561.5 W L^-1.?3?A light weight graphene-carbon nanotube foam?TRGN-CNTs-F?with high electric conductivity has been successfully fabricated by pyrolyzing commercial polyurethane?PU?sponge coated with CNTs and GO.Moreover,advanced electrode of the NiCo₂O₄ nanosheet supported on NSCS has been successfully fabricated through hydrothermal method combined with annealing treatment.A further electrochemical deposition was conducted to grow Ni?OH?₂ on the surface of NiCo₂O₄ nanosheets,and a core-shell structure NiCo₂O₄@Ni?OH?₂/TRGN-CNTs-F was successfully fabricated.The electrode exhibits high gravimetric capacitance of 1810 F g^-1 and high volumetric capacitance of 790 F cm^-3 with excellent cycling stability.A high performance asymmetric supercapacitor was successfully fabricated by using NiCo₂O₄ @Ni?OH?₂/TRGN-CNTs-F as positive electrode and NGN/CNTs film as negative electrode,exhibiting high gravimetric energy density of 54 Wh kg^-1 at 799.9 W kg^-1 and high volumetric energy density of 37 Wh L^-1.