Design And Synthesis Of Carbon-based Electrodes And Construction Of Flexible Supercapacitors

Supercapacitors and batteries are today’s two main energy storage components.Compared with batteries,supercapacitors have a series of advantages such as high power density,long life,wide operating temperature limit,maintenance-free,environmental protection,and energy saving.It has broad application prospects in fields,medical equipment and wind power generation.At present,the main challenge facing the research of supercapacitors is still how to improve its energy density,and how to improve its mechanical properties and flexibility while ensuring its high capacity is also the current focus of research on supercapacitors.Traditional supercapacitor electrodes are usually prepared by using stainless steel mesh,copper mesh,aluminum foil or foamed nickel as the conductive current collector,and then combining the conductive current collector with electroactive materials.The choice of rigid current collector destined that the electrode prepared by this method does not have any flexibility and toughness,resulting in the prepared supercapacitor basically without any deformability.Therefore,abandoning inherently rigid materials and developing conductive current collectors with high capacitance and flexibility has become a top priority.In this paper,graphene and carbon fiber are the research objects,and the carbon-based self-supporting electrode and its application in flexible supercapacitors are studied in detail.The specific content and results are as follows:（1）In the second chapter of the paper,a graphene/Co Mo O₄ nanosheet electrode was proposed and synthesized.Compared with the nickel foam of the same structure,the three-dimensional graphene foam has better flexibility.Graphene foam with a three-dimensional（3D）network structure of nickel foam was prepared by chemical vapor deposition（CVD）of graphene on the surface of nickel foam and then removing nickel by acid etching.Then,the active material is uniformly grown on the network skeleton of the 3D graphene foam,which greatly improves the utilization rate of the electrode.Its unique structure also increases the contact between the electroactive material and the electrolyte interface,making the pseudocapacitance reaction fully occur.Due to the high electron transfer rate of graphene and the high activity of Co Mo O₄ nanosheets,the 3D composite electrode has excellent electrochemical performance,relatively high area specific capacitance（2737m F/cm² at 1 m A/cm²）and excellent cycle stability,the capacitance of the supercapacitor based on the composite electrode is basically unchanged when it is bent 90°to 180°.（2）Wearable electronic equipment often undergoes mechanical deformation in actual use,which may cause the fracture or even failure of the flexible supercapacitor,which will significantly shorten the service life of electronic equipment and cause a large amount of electronic waste that is harmful to the environment.Flexible self-healing supercapacitors that recover in the case of structural damage are also particularly important.In order to prepare a flexible self-supporting substrate with high specific capacity to fundamentally improve the electrochemical performance of the electrode,the third part of the thesis chooses to use commercial carbon cloth as raw material,and prepares a material with excellent physical and chemical properties through a medium-temperature air calcination method.Compared with commercial carbon cloth,the specific capacitance of activated carbon cloth is increased by more than 200 times,reaching 1816 m F/cm².In order to achieve self-healing properties,the traditional polyvinyl alcohol（PVA）-H₂SO₄ gel electrolyte is simply freeze-thaw modified and assembled with activated carbon cloth to form a flexible supercapacitor,which not only exhibits a high area specific capacitance,but also has a good Flexibility and mechanical properties.When the device is bent from 45°to 180°,its electrochemical performance remains basically unchanged.Thanks to the large number of dynamic hydrogen bonds in the gel electrolyte,the device can realize self-healing after cutting,and can maintain high capacitance performance.（3）The modified carbon cloth in Chapter 3 of the paper can be used directly as the electrode of a flexible supercapacitor,but also as a base material for growing various electrochemically active materials.In order to further improve the electrochemical performance of solid-state supercapacitors,the modified carbon cloth prepared in the second part of the paper was used as the substrate,and a high-area specific capacity Mn O_X/porous carbon cloth composite was synthesized by in-situ growth by hydrothermal and wet chemical methods.material.Among them,the area specific capacitance of the Mn O₂/CC₅₀₀ electrode at1 m A/cm² can reach 2555 m F/cm²,and the flexible all-solid supercapacitor assembled based on Mn O₂/CC₅₀₀ and the healable PVA-H₂SO₄ gel electrolyte can provide 886.7 m F/cm²Capacity.The capacity retention rate can be maintained at 87.69%after 10,000 constant current charge-discharge cycles,and the capacity retention rate is 79.24%after cutting at the same position and self-healing 5 times,showing excellent flexibility and self-healing performance.In general,this thesis has prepared flexible electrode materials based on graphene foam and carbon fiber cloth by chemical vapor deposition,hydrothermal,medium temperature air activation,and wet chemical methods,aiming to ensure the construction of supercapacitors while maintaining high energy density.Flexible supercapacitors with high mechanical properties.The above design and methods provide theoretical guidance and scientific methods for the preparation of high-performance electrochemical energy storage materials,and the constructed flexible all-solid-state supercapacitors have good prospects in the application of flexible electronic products in the future.