Construction And Performance Of Hybrid Supercapacitor Based On Transition Metal Componds

The rising consumption of fossil fuel is one of important problems of the sustainable development of human society.Green and renewable energy sources,such as solar energy,wind energy and tidal energy,are needed to exploit to meet the demands of human beings.These green energy sources usually depend on the weather condition.In order to solve this problem,energy storage devices are needed to realize the energy storage and conversion.At present,energy storage devices mainly include traditional batteries,supercapacitors and lithium ion batteries.Among these devices,supercapacitors become a hot spot due to theirs high power density,specific capacitance,and good cycle stability.The performance of the supercapacitors is determined by the performance of electrode materials.Meanwhile the performance of electrode material is closely related to the structure,morphology,and electrical conductivity.Metal componds has a high theoretical specific capacitance,but they have some inherent shortcomings.Firstly,most of the transition metal componds are poor in electronic conductivity,which result in poor rate performance and low power density.Secondly,the collapse of electrode material generated by the structural change during the charging/discharging process leads to poor cycle life.Thirdly,the transition metal compounds usually show small specific surface area,resulting in smaller specific capacitance.In this paper,to solve these problems,a series of original research about the design,controllable preparation of the new electrode materials,and the construction of hybrid supercapacitor is carried out.(1)A hybrid capacitor based on the yolk-shelled NiCo2O4 sphere(YS-NiCo2O4)was constructed.The solid spherical S-NiCoA precursor,prepared by the solvothermal method,was transformed into the yolk-shelled NixCo2x(OH)6x through a hydrolysis process.And YS-NiCo2O4 can be obtained by further calcination.XRD,TEM,SEM,XPS and nitrogen adsorption and desorption tests were used to study the crystalline phase transformation,morphology,valence state,specific surface area and pore size distribution of YS-NiCo2O4.Cyclic voltammetry,galvanostatic charge-discharge and cycle life of YS-NiCo2O4 were also performed.The YS-NiCo2O4 show a high specific capacitance of 835.7F g-1 at 0.5A g-1.The capacitance retention of YS-NiCo2O4 was about 93%after 10,000 cycles.The energy density of hybrid supercapacitor based on YS-NiCo2O4 and graphene is as high as 34.7Wh kg-1 at 0.5 A g-1.Even at a high power density of 11697 W kg-1,the hybrid supercapacitor still deliver energy density up to 12.1 Wh kg-1.(2)A hybrid supercapacitor device with excellent energy density based on the graphene@MnO2 nanosheet(G@MnO2)composite as the cathode material and the porous graphene as the anode material was constructed.The negatively charged MnO4-can adsorb on the surface of positively charged PANI-functionalized graphene through strong electrostatic interaction.The combined effect of self-sacrificing template of PANI and MnO4-in-situ nucleation result in G@MnO2.XRD,Raman,and TEM were used to investigate the crystal structure transition and the morphology of the G@MnO2.The morphology and mesopore feature of G@MnO2 were confirmed by SEM and N2 adsorption and desorption tests,respectively.The preparation mechanism based on self-sacrificial template of polyaniline is proved by XPS and EDX.G@MnO2 composite exhibits a high specific capacitance of 245.0F g-1 at0.5A g-1.Benefited from the ample electrochemical sites and short ion diffusion paths,the capacitance can reach 182.4F g-1 even at high current density of 20A g-1.In particular,benefited from the well-match of G@MnO2 and porous graphene with the similar electrochemical performance,the energy density of the hybrid ultracapacitor reaches 30.6Wh kg-1,and the energy density of 7.9Wh kg-1 can be maintained even at a high power density of 11804W kg-1.(3)CNT/Ni(OH)2composite with high specific capacitance and enhanced rate performance was prepared through the electrostatic interaction between positively charged Ni(OH)2 nanosheets and negatively charged carbon nanotubes,and a hybrid capacitor based on CNT/Ni(OH)2 composite was achieved.The crystalline phase,morphology and mesopore feature of Ni(OH)2 and CNT/Ni(OH)2 were investigated by XRD,TEM and SEM,respectively.The strong interaction between CNT and Ni(OH)2 was confirmed by FTIR.In the traditional three-electrode system,the composite electrode material shows a high specific capacitance of 1360F g-1 at a current density of 0.5A g-1 in a 2 M KOH solution.The maximum energy density of hybrid supercapacitor based on CNT/Ni(OH)2and porous graphene was 56.8 Wh kg-1.When the hybrid supercapacitor device operates at a power density of 11697W kg-1,the energy density can still reach 24.7Wh kg-1.(4)A hybrid capacitor with high energy density was constructed based nitrogen-doped graphite nanosheet(NG)as the negative electrode and nitrogen-doped graphene manganese dioxide composite(NG@MnO2)as a positive electrode.Firstly,the metal-organic framework ZIF-8was loaded on the surface of graphene oxide to form graphene oxide ZIF-8 composite without any surfactant,which was calcined to form NG.And furtherly NG was used as the substrate of NG@MnO2.The temperature influence on NG was investigated,and the optimal calcination temperature was 800?.Then,the NG obtained under the optimal temperature was used as a precursor to generate NG@MnO2 by the in-situ redox reaction between potassium permanganate and carbon.The crystal structure conversion and morphology change of NG and NG@MnO2were studied respectively by XRD,and TEM.The elemental distribution and carbon content of NG@MnO2were studied by EDX.The maximum specific capacitance of NG reached 225.0F g-1,and the specific capacitance of NG-800 was up to 174F g-1 at 20 A g-1.The maximum specific capacitance of the NG@MnO2 composite can reach 157.1 F g-1.The operating voltage of the hybrid supercapacitor device based on NG and NG@MnO2 can reach 2.0V,and the maximum energy density can reach 19.5Wh kg-1.(5)A high energy density hybrid capacitor based on CNT/NiCo LDH was constructed.CNT/NiCo LDH with high energy density and enhanced rate performance was prepared by a co-precipitation method.The crystalline and morphology of NiCo LDH were investigated by XRD,TEM and SEM.The strong interaction between carbon nanotubes and NiCo LDH was confirmed.CNT/NiCo LDH show a high specific capacitance 1614F g-1 at 0.5A g-1 in the 2 M KOH solution.Even at 20 A g-1,the specific capacitance can reach 1398 F g-1,?87%of the initial capacitance,which is higher than 60%of pure NiCo LDH.Based on the good match between the CNT/NiCo LDH and NG,the maximum energy density of the hybrid supercapacitor device is up to 47.4Wh kg-1.The device still delivers an energy density of 17.8 Wh kg-1 at the ultra-high power density of 13205 W kg-1.(6)Cobalt/nickel layered double hydroxide@CNTs composite intercalated by 2-methylimidazole was applied in hybrid supercapacitor.Using precursor of cobalt nitrate hexahydrate,nickel nitrate and 2-methylimidazole,CoNi LDH@CNTs composite is prepared based on the basic characteristics of 2-methylimidazole and the intercalation effect,and show excellent specific capacitance and rate performance.The specific capacitance is as high as 1823.7 F g-1 at a current density of 0.5 A g-1.Even at a current density of 20 A g-1,the capacitance retention is as high as 92.9%.After 5000 cycles at a current density of 10 A g-1,the specific capacitance still remains 49%,which is much better than that of CoNi LDH16%.The maximum energy density obtained by hybrid supercapacitors based on NiCo LDH@CNTs and NG is 49.2 Wh kg-1.The hybrid supercapacitor can delivery energy density up to 23.0Wh kg-1 at ultra high power density of 14279 W kg-1.