Fabrication And Research Of Metal Oxide Nanomaterials-based Electrode For Supercapacitors

As a new generation of energy storage devices,supercapacitors have been widely concerned because of their characteristics such as fast charge and discharge,high power density and excellent cyclic stability.However,due to the relatively low energy density,the applications of these devices are limited.To this end,researchers hope to improve the energy density of supercapacitors and maintain their high power density by optimizing the electrode materials and electrolytes.By preparing better electrode materials to obtain supercapacitors with high energy density and power density at the same time,it is necessary to have a deep understanding and mastery of the energy storage mechanism of the electrode.Nanomaterials have become popular candidates for the preparation of supercapacitor electrode materials because of the rapid redox reaction and the reduction of ion transmission paths,as well as the improvement of electrochemical active points.Metal oxide nanomaterials have high theoretical specific capacitance with promising application prospect.The purpose of this paper is to design and prepare several metal oxide nanomaterials with different components,morphology and dimensions for supercapacitor electrode materials by using simple and effective synthesis methods.The main research contents and results are as follows:1.Using hydrothermal reaction and high temperature to grow ZnCo₂O₄ active materials on Ni foam.It finds that active materials will tend to form denser stuctures with an increasing amount of NH4F in the solution system.We obtained four different morphologies of ZnCo2O4:nanoneedles,thin nanoneedles-clusters,thick nanoneedles-clusters,and lozenge-like bulks.ZnCo₂O₄ with the thin nanoneedles-clusters morphology holds the best electrochemaical performance with a 2.77 F/cm² at the current density of 5 mA/cm².A button asymmetric supercapacitors?ZnCo2O4-2/NF//AC/NF?assembled with ZnCo2O4-2/NF and AC/NF exhibit excellent performances in energy storage.The button asymmetric supercapacitors can achieve an energy density of 114.49 uWh/cm² at power density of 4001.59 uW/cm² and a power density of 24000 uW/cm² at energy density of 80uWh/cm².2.ZnCo₂O₄ ultra-thin curved sheets which directly grown on nickel foam are fabricated by a one-step hydrothermal method.A possible growth mechanism for the ZnCo2O4ultra-thin curved sheets involves sodium dodecyl sulfate chains serving as the template under the adsorption of the hydrophilic terminal on Zn²⁺and Co³⁺ions.Active materials grow along the chains after nucleation,these chains in turn attached to each other forming ultra-thin curved sheets in the reaction solution.The ZnCo₂O₄ ultra-thin curved sheets/nickel foam electrode exhibits super-high specific capacity of 832 C/g at 5 A/g,remarkable high-rate capability?737 C/g at 15 A/g?,excellent cycling stability and maintaining 85.5%at 50 A/g after 5000 cycles.A button hybrid supercapacitor device operating at 1.7 V is prepared by using activated carbon coating on nickel foam and ZnCo₂O₄ ultra-thin curved sheets/nickel foam as negative and positive electrodes,respectively.The device shows an energy density of 20.31 Wh/kg at a power density of 855W/kg while maintaining an energy density of 10.2 Wh/kg at 4.25 kW/kg,as well as good cycling stability?87%retention after 5000 cycles?.3.We proposed MnO₂ thin nanosheets assembled nanospheres with pre-insertion Na ions and oxygen vacancies(NaMnO_2-x)as highly capable supercapacitor electrodes.The NaMnO_2-x electrode can reach a stable potential window of 1.2 V without oxygen evolution reactions in three-electrode configuration.The voltage window of the assembled aqueous ASC device can be expanded to 2.4V?1M Na₂SO₄?by using NaMnO_2-x electrode and activated carbon electrode as positive and negative electrodes,respectively.The NaMnO_2-x-x is prepared by hydrothermal method and annealing treatment in N_2.The NaMnO_2-x electrode delivers a good specific capacitance of 215 F/g at current density of 1A/g.It displays high-rate capability and an excellent cycling stability,maintaining 95.5%of its initial specific capacitance at 2A/g after 2500 cycles.The ASC device shows a high energy density and power density of 28.56 Wh/kg and 1246 W/kg,respectively,at a current density of1A/g.