| NiCo2O4 is a inverse spinel structure with rich active sites,low material cost,the elements are widely distributed and environmental friendly features.When applied to super capacitor,it has higher theoretical specific capacitance(1400 F/g),larger than power density and energy density,which has become new research hotspot of electrochemical energy storage materials.But it is considered that the morphology of NiCo2O4 will have an effect on the electrochemical performance and the material was limited by electrical conductivity,etc,resulting in poor cycling stability of electrochemical,which limits its application.In this paper,using the hydrothermal method by controlling hydrothermal reaction time and the amount of precipitation agent to explore explore the transformation law of NiCo2O4 morphology.Hollow urchin-like NiCo2O4 with specific surface area is as large as 158.57 m2g-2 was synthesized by the simple hydrothermal approach.When hollow urchin-like NiCo2O4 was applied as electrode material for sodium-ion batteries and lithium-ion batteries,the hollow urchin-like NiCo2O4 microspheres delivers very high specific capacitance of 991 mAh·g-1 after 50 cycles in LIBs and 285 mAh·g-1 after 100 cycles at a current density of 100 mA·g-1 for SIBs.Because the hollow urchin-like NiCo2O4 microspheres are fabricated by the mechanism of the 10 nm consisting of nano needle self-assembly into nanoparticles.The hollow and a large number of pores can not only alleviate the volume change in the charge and discharge process,but also the nanocrystalline particles can shorten the diffusion path.By adjusting the hydrothermal time,exploring the rule of morphological transformation of cobalt nickel under excessive urea.With the extension of hydrothermal reaction time,our kinds of sea urchin like,three dimensional flower,sheet and lump were prepared.The transformation is caused by the Ni/Co ion ratio.The specific capacitance of sea urchin,three dimensional flower,sheet and bulk were 912 F/g,392.2,277.4 and 277.4 F/g,respectively,when were tested for supercapacitor performance at current density of 1 A·g-1,which indicating that there was a great relationship between capacitance and morphology.The three-dimensional porous carbon(3D-OPC)was prepared by NaCl as a template and combined with NiCo2O4 by hydrothermal method.The composite samples were used as cathode materials,and three dimensional porous carbon materials were assembled as negative electrodes to form asymmetries capacitors(NiCo2O4/C-C).Non-composite nickel cobalt oxide as the positive material,the three-dimensional porous carbon as the negative assembly of the asymmetric capacitors(NiCo2O4-C),and make a performance comparison between NiCo2O4/C-C and NiCo2O4-C.The asymmetrica capacitor of NiCo2O4-C has a specific capacitance of 47.6 F/g under 1 A·g’1 current density.The specific capacitance of NiCo2O4/C-C at 1 A·g-1 current density can reach 82.2 F/g.Not only is the increase of the capacitance,but also the cyclic and energy density are also superior to the unsymmetrical NiCo2O4 as the positive materia.Not only the specific capacitance is increased,but also the cycle life is improved.This will give high capacitance and enhanced electrochemical kinetics relative to carbon increases the conductivity of the electrode material and the relatively small diameter of the NiCo2O4 nanoneedle porous carbon structure could facilitate the ion transport for the charge and discharge processes. |
PDF Full Text Request