Loading Of Mn-Co Compounds On Carbon Network And Its Electrochemical Properties

In recent decades,economic and social development and population growth have greatly increased the consumption of natural resources and dramatically reduced the storage of non-renewable resources,while also exacerbating the problem of environmental pollution.The development of ultracapacitors is an important step for human beings toward solving the environmental and energy crisis resulting from the heavy dependency on increasingly consumed to fossil fuels.As green secondary energy storage devices with long circulation life,fast charge/discharge,high power density and low cost,supercapacitors are widely used in the fields of smart grid systems,urban rail transportation,solar energy systems,new energy vehicles,etc.However,there are still challenges in developing excellent electrode materials.In this paper,we obtained bendable,foldable carbon cloth（CC）with low resistance value by high-temperature carbonization of commercially available cotton cloth,then used CC as the base material,loaded Mn and Co compounds on its surface,and obtained CC/MnCo₂O₄ composite electrode material without binder after heat treatment.This method of growing the active material directly on the fiber surface without binder,while using the self-supporting and electrochemical activity of the substrate material,results in a high-performance composite electrode material of supercapacitor.The CC/MnCo₂O₄ precursor,which was grown directionally and tightly wrapped,was prepared by a one-step hydrothermal method using CC as the substrate,followed by heat treatment at 350℃to obtain the CC/MnCo₂O₄-1 composite.The hydrothermal temperature,time and the amount of NH₄F added to the reactant affected the morphology and encapsulation of the active material.With the increase of NH₄F addition,the CC surface loading showed a trend from blocky cubes to vertical nanoneedles to tilted cross-grown nanoneedles;with the increase of time,the active material coated on CC gradually changed from blocky to nanoneedles and tightly wrapped CC;with the increase of temperature,the nanowires gradually wrapped complete at a temperature of 120℃with the addition of 3.0 mmol NH₄F hydrothermal reaction for 6 h to obtain the best morphology.The nanowires exhibit polycrystalline nature and are composed of small particles of about 5-10 nm.CC/MnCo₂O₄-1 supercapacitor composites has good multiplicity and has a maximum specific capacitance of 960.18 F/g,and a specific capacitance retention of 86.10%after 1000cycles at 5 m A/cm² current density.Mn-Co-Organic ligands or Co-Organic ligands were produced under hydrothermal room temperature and hydrothermal conditions at 120℃respectively.Further reactions were followed by heat treatment at 350℃to obtain CC/MnCo₂O₄-2 in nanowire form,CC/MnCo₂O₄-3 in thin flaky nanosheets and CC/MnCo₂O₄-4 in triangular flaky nanosheets,respectively.All three exhibited polycrystalline nature with uniform distribution of Mn,Co and O elements on CC.70nm diameter nanowires were wrapped around the surface of CC/MnCo₂O₄-2,and the nanowires formed a mesh structure between some CC fibers,and these nanowires consisted of 5-15 nm small particles;2 nm thick nanosheets were grown vertically on the surface of CC/MnCo₂O₄-3,and these nanosheets consisted of 5-10 nm small particles.Consisted of small particles of 5-15 nm,and the mesh-like pore structure was spread throughout the nanosheets;the triangular nanosheets of CC/MnCo₂O₄-4 with a surface thickness of 20 nm were grown vertically in layers,and the small particles of 5～15 nm formed nanorods of about 20 nm in diameter,and these nanorods further formed the triangular nanosheets.The electrochemical test results of CC/MnCo₂O₄-2,CC/MnCo₂O₄-3,and CC/MnCo₂O₄-4showed excellent capacitance performance,and the CC/MnCo₂O₄-2 composites had a maximum specific capacitance of 828.57 F/g at a current density of 1 m A/cm² and a specific capacitance retention of 828.57 F/g after 1000 cycles at a current density of 5 m A/cm².The CC/MnCo₂O₄-3composite has a current density of 1 m A/cm² with a maximum specific capacitance of 953.32 F/g and a specific capacitance retention rate of 86.91%after 1,000 cycles at a current density of 5m A/cm².The CC/MnCo₂O₄-4 composite possesses a maximum specific capacitance of 776.18F/g at a current density of 1 m A/cm² and a specific capacitance retention of 77.94%after 1000cycles at a current density of 5 m A/cm².In this thesis,the effects of reaction time,temperature and NH₄F addition on the morphology of Mn and Co compounds loaded on CC during the one-step hydrothermal process were explored to prepare CC/MnCo₂O₄-1 composites grown in situ on the surface of nanoneedle vertical CC fibers.The nanowire CC/MnCo₂O₄-2,thin nanosheet CC/MnCo₂O₄-3,and triangular sheet CC/MnCo₂O₄-4 composites were prepared and electrochemically tested using the Organic ligands structure.The CC/MnCo₂O₄ binder-free composites prepared in this paper have great potential for supercapacitor electrode materials and offer the possibility of commercialization.