Preparation And Electrochemical Properties Of Nickel-zinc-based Metal Complex Nanomaterials

Nickel-based composites are one of the excellent candidates for supercapacitor electrode materials due to their high capacity,excellent electrical conductivity and roughness.Zinc itself does not have the redox properties,but can form a synergistic effect with nickel.At the same time,the use of metal cations and different anions have complementary advantages to optimize performance.However,one of the obvious disadvantages of the traditional transition metal oxides or hydroxides is their low conductivity.Therefore,two different approaches have been devised to solve this problem.This dissertation mainly focuses on the synthesis of nickel-zinc-based nanocomposites and their research and improvement in supercapacitors（SC）.By regulating the morphology of the material,optimizing the conductivity,resulting in excellent specific capacitance,rate performance and durability.The main research content is as follows:1.Rational sulfur-doped nickel zinc hydroxyl carbonate（NZSC-4）even-distributed nanoparticles are prepared by a simple two-step hydrothermal method,getting high degree of dispersion of nickel zinc hydroxyl carbonate（NZC）precursor and then sulfidizing to increase conductivity.Meanwhile,its large specific surface area of 226 m² g^-1,resulting in a large number of redox sites,can effectively reduce volume change during charge-discharge process.As a positive electrode material,NZSC-4shows high capacitance value of 1634 F g^-1 at 1 A g^-1 and outstanding rate performance(73%rate retention at 20 A g^-1).What’s more,an all-solid-state asymmetric supercapacitor（ASC）was assembled,using NZSC-4 as positive electrode and activated carbon as negative electrode.The ASC exhibits a high energy density of36.17 Wh kg^-1 from a high voltage range of 0 to 1.7 V at a power density of 0.85 kW kg^-1,appropriate leakage current and self-discharge.Two fully charged ASCs（in series）can effectively power a white light emitting diode（LED,operating voltage greater than3 V）,and then can still supply yellow and red LEDs after the white bulb has consumed some of the energy.Therefore,NZSC-4 as a pseudocapacitance material looks promising with potential application value.2.The mulberry-like carbon dot（CD）/nickel-zinc phosphate complex is formed by the reaction of sodium pyrophosphate and pre-prepared carbon dots.This appearance is similar to that of a zero-dimensional nanoparticle.It was observed by HRTEM that the CD is mainly located on the surface of the material.Such a structure will allow the CD to fully contact the electrolyte when it is fabricated into an electrode material.Given that different concentrations of carbon dots doped phosphate show different morphologies,they also show different properties,indicating that the concentration of CD is very sensitive to the material.The synthesized mulberry-like composite NZP-10 nanomaterial has a high specific capacitance of 1885.7 F g^-1 at a current density of 1 A g^-1 and still has 98.7%of the initial capacitance after 3,000cycles,which is mainly due to the presence of mulberry-like nickel zinc phosphate structure and CD greatly improves the stability of the material.The ASC device was assembled using NZP-10 as the positive electrode and the negative electrode coated active carbon,and it had a high specific capacitance(89.2 F g^-1)and a high energy density of 33.7 Wh kg^-1(when the power density reached 824.9 W kg^-1).In summary,this article mainly studied the synthesis and electrochemical performance of nickel-zinc-based metal materials,and adjusted the morphology with sulfur or CD to obtain better results.The various advantages exhibited by nickel-zinc-based metal materials make it a potential new generation of energy storage materials.