Study On The Preparation Of Ni(OH)₂/C Composite Material And Its Application In Supercapacitors

Supercapacitors have broad application prospects in the field of energy storage because of their advantages such as high power density,fast charge and discharge and long cycle life.Electrode materials are the core components of supercapacitors,and their chemical composition and micro/nano structure largely determine the performance of supercapacitors.Therefore,the design and preparation of electrode materials have become the current hotspot.Among kinds of electrode materials,Ni(OH)2 has a large specific capacitance due to its faraday reaction,so it is widely used as electrode materials for supercapacitors;however,its poor conductivity reduces its performance in practical applications.To solve this problem,Ni(OH)2 was combined with carbon materials in this paper,and by designing reasonable micro/nano structures,it aims to improve the specific capacitance and cycling stability of the materials.The main research contents and results of this paper are as follows:(1)The core-shell nanocomposites of N-doped carbon spheres(NCSs)and CoxNi1-x(OH)2 were successfully designed and synthesized by a fast and simple twostep method.Firstly,regular NCSs are directly derived from carbonization of polydopamine,which offer conductive cores for fast electronic transport.Then,the CoxNi1-x(OH)2 nanosheets are vertically grafted on the surface of NCSs substrate by a chemical bath deposition method.To get the homogeneous bimetal hydroxides CoxNi1x(OH)2,the influences of cobalt doping content,different kinds of oxidants and different synthesis paths on the morphologies,structure and capacitance properties of hybrids are further analyzed.Results show that the obtained NCSs@CoxNi1-x(OH)2 composite with 5%Co doping,K2S2O8 as the oxidant and simultaneous cobalt doping exhibits impressively enhanced specific capacitance(2065 F g-1 at 1 A g-1 and rate capability(1429 F g-1even at 45 A g-1)than NCSs@Ni(OH)2.The outstanding capacitive performance of this kind of nanocomposite is due to its large surface area,optimum porous size distribution and flower-like morphology,especially the high electrical conductivity originating from conductive skeleton of NCSs and Co ion doping.Furthermore,using the optimized NCSs@CoxNi1-x(OH)2 and activated carbon as the positive and negative electrode respectively,the prepared hybrid supercapacitor achieves higher energy(16-37 Wh kg-1)and power density(8-0.4 kW kg-1),along with relatively good cycling stability.(2)Ni(OH)2/CC composites were prepared by in-situ growth of Ni(OH)2 nanosheets on carbon cloth(CC).The effects of synthesis method and reaction time on the morphology and electrochemical properties of the composites were investigated.In order to improve the properties of the materials,Ni(OH)2/CC was modified by plasma etching technology.The results show that the porous Ni(OH)2 nanosheets have a specific capacitance of 2600 F g-1 and enhanced cycling stability at l A g-1 at the plasma etching time of 3 min.Its excellent electrical properties can be attributed to the porous structure formed and the strong interaction with CC.In addition,the NiFe Prussian blue analogue(NiFePBA)was compounded with Ni(OH)2/CC to form NiFePBA@Ni(OH)2/CC composite.The effect of loading time on the properties of composites was investigated.The specific capacitance of the prepared NiFePBA@Ni(OH)2/CC at 1 A g-1 is 1606 F g-1 when the loading time is 12 h.Finally,the best Ni(OH)2/CC composite material and activated carbon were assembled into supercapacitors.When the power density was 400-8023 W kg-1,the energy density was 47-15.6 Wh kg-1,showing a good application prospect.