Preparation Of Graphene Based Electrodes Materials And Research Of Supercapacitor Properties

Nowadays,with the booming development of advanced process technology,electronic devices are moving toward miniaturization and intelligence,which puts new requirements on their energy supply systems.Supercapacitors can be charged and discharged rapidly,with a high output power density in a safe and stable way.So,it’s a strong candidate for the next generation of energy storage devices.As a key component,the energy storage performance and stability is directly influenced by the electrode materials.Graphene-based materials with superior electrical conductivity,a high specific surface area,excellent mechanical properties and stable electrochemical properties have become a hot topic of research in the last few years.However,the graphene preparation process is complicated,costly,and prone to agglomeration during the preparation process,limiting its application and production significantly.Based on this,the purpose of this thesis is to investigate a simple and efficient graphene oxide（GO）reduction process and improve the energy density and power density of graphene-based cathode materials through doping alteration in order to satisfy the practical application requirements.The details are as follows.（1）The reduced graphene oxide（FRGO）prepared by the flame reduction method offers a large specific surface area and a rich pore structure,which facilitates the diffusion and transport of electrolyte ions.It has better wettability with the electrolyte than graphene prepared by hydroiodic acid reduction and high temperature reduction.At a current density of 0.2 A g^-1,the specific capacity is 204.3 F g^-1,and the maximum energy density and power density are 14.2 Wh kg^-1 and 24.7 k W kg^-1,respectively.After 10000cycles,it still retains 81.1%of its capacity,showing a good cycling stability.In addition,the device is configured as a fork finger structure with a capacity of 100.4F g^-1 at 0.2A g^-1,which has great performance and can meet the application requirements of various scenarios.（2）Based on the high pseudo-capacitance characteristics of manganese tetroxide（Mn₃O₄）,FRGO@Mn₃O₄ composites were successfully synthesized by in situ growth of Mn₃O₄nanoparticles on the surface of FRGO by colloidal co-precipitation.After doping,the Mn₃O₄ particles and graphene lamellae form a three-dimensional network structure that is beneficial to the rapid transport of electrolyte ions and exhibits a high specific capacitance(323.5 F g^-1)with the addition of pseudo-capacitance.Additionally,the assembly of asymmetric supercapacitors with activated carbon（AC）extends the operating potential window of the device（1.5 V）and enables a maximum energy density of 22.6 Wh kg^-1 at 150.5 W kg^-1.After 400 bending cycles,the capacity retention rate reached 90.6%,indicating good bending stability.Furthermore,the sandwich and forked finger structures are combined to form the sandwich-forked finger structure device which has better energy storage performance,but also has super high cycle stability,with 92.9%capacity after 40,000 charge/discharge cycles.（3）Fluffy amorphous graphene composites material modified with 2-hydroxy-1,4-naphthoquinone（HNAQ）molecules were created by hydrothermal way.Its electrochemical performance is studied by assembling zinc ion hybrid supercapacitors.Among these,graphene offers a porous structure and good electrical conductivity,and HNAQ molecules,through redox reaction with Zn²⁺,offer an extremely high pseudocapacitance.The RGO@HNAQ exhibits a remarkable capacity of 235.3 m Ah g^-1at 0.3 A g^-1,which is significantly more than that of the RGO materials(142.8 m Ah g^-1).And the device realizes an ultra-high energy density of 191.9 Wh kg^-1and high power density(28.6 k W kg^-1).What’s more,because of the exceptional cycling stability,it shows a high capacity retention rate（89.8%）after 10000 cycles.Compared to the sandwich device,the sandwich-fork-finger ZIHC has higher capacity and energy density(316.2m Ah g^-1 and 292.3Wh kg^-1),further demonstrating the superiority of this structure.Additionally,the sandwich flexible device has a capacity retention rate of 95.1%even after 600 cycles of bending,demonstrating outstanding electrochemical bending stability.