Design And Construction Of High Performance Aqueous Wide Voltage Asymmetric Supercapacitors

The current challenge of supercapacitors（SCs）is how to promote the energy density without sacrificing their high-power-density and outstanding cycle life.Asymmetric supercapacitors（ASCs）can substantially broaden their working voltage windows benefiting from the advantages of both cathode and anode,while breaking through the energy storage limitations of corresponding symmetric cells.Wide voltage aqueous ASCs hold great promise for future electronic systems that requires satisfied energy density,power density,and cycle life,due to the advantages of aqueous electrolyte in terms of low cost,operational safety,facile manufacture,environment-friendly,and high ionic conductivity.This dissertation will first briefly present an overview of the historical developments,charge storage mechanisms and matching principles of wide voltage aqueous ASCs.Then we summarize the cathode and anode materials with wide potential windows for building wide voltage aqueous ASCs over the last few decades.The next section details the optimization methods of aqueous electrolytes related to wide voltage aqueous ASCs.Besides,the basic device configurations of wide voltage aqueous ASCs are classified and discussed.Furthermore,we propose several strategies for achieving high-performance wide voltage aqueous ASCs in voltage window,specific capacitance,rate performance and electrochemical stability.Finally,to motivate the further research and development,several key scientific issues and technical difficulties are discussed.Focusing on the problems and challenges faced by the wide voltage aqueous ASCs,this dissertation studies the key electrode materials,the matching of positive and negative electrodes and the energy storage mechanism for building high-performance aqueous ASCs devices.The details are as follows:1.Although the electrochemical performance of traditional hollow nanostructured transition metal oxide electrode has been greatly improved compared with its bulk material,it is still difficult to meet the needs of high energy density supercapacitors.In this dissertation,hollow Co₃O₄ supraparticle composites were prepared by dopamine self-assembly of Co₃O₄ nanoparticles,which not only have higher specific surface area,but also form a continuous carbon network between the ultra-small nanoparticles and substrates.When applied into supercapacitors,they have high specific capacitance,superior rate performance and excellent electrochemical stability.2.The design and preparation of cathode and anode materials with wide potential window and high specific capacitance is the key to construct wide voltage aqueous ASCs with high energy density.There have been a lot of reports on high performance cathodes,but it is still a challenge to prepare anodes that match them in terms of voltage window and capacitance.In this dissertation,a hierarchical structure of carbon coated porous VN anode with wide voltage（-1.3-0 V）and high specific capacitance(605 F g^-1)was constructed to match Na_0.5MnO₂ cathode(0-1.3 V,557 F g^-1.The assembled aqueous asymmetric supercapacitor exhibited a wide voltage window of 2.6 V and a high energy density of 96.7 Wh kg^-1.3.It is difficult for traditional supercapacitors to break through the barrier of low energy density due to the energy storage mechanism that they only react on the surface of materials.Aqueous Zn-ion capacitors integrate the advantages of traditional supercapacitors and batteries.Through the deposition/stripping of Zn ions on the Zn anode and the highly reversible adsorption/desorption of Zn ions on the carbon-based cathode,they simultaneously have the high energy density and power density.In this dissertation,N-doped hierarchically porous carbon spheres were prepared by the co-assembly of dopamine and block copolymer.The hierarchically porous structure provides more isotropic diffusion channels and ion diffusion paths for Zn ions,shortens the transmission distance and minimizes the transmission resistance for ultra-fast Zn ions storage.The energy density of the as-prepared Zn-ion capacitor can reach 144.3Wh kg^-1 with ultrahigh power density(79.9 k W kg^-1)and rate performance.