Preparation And Electrochemical Properties Of MnO₂/C Flexible Composite Electrode Materials

The environmental pollution and global energy shortage have brought about an urgent requirement to develop sustainable clean energy,especially for wind energy,tidal energy,solar power and so on.The energy storage devices with high performance and flexibility are essential to modern society due to increasingly requirement in portable,wearable and implantable electronic devices.In order to further improve the energy density of supercapacitor,manganese metal oxide（MnO_x）as pseudocapacitors electrode materials has been widely concerned.MnO₂ is a particularly attractive material for application in supercapacitors due to its low cost,environmental friendliness,simple synthesis process and extremely high theoretical specific capacitance.However,the electrochemical performances of MnO₂ in supercapacitors are usually far below the theoretical performance due to its low electric conductivity.The carbon-based materials（carbon nanotubes,activated carbon,graphene,etc.）can be used for energy storage applications due to their excellent electrochemical performance,such as high electrical conductivity,high electric double layer capacitance and excellent chemical or physical stability.Thus,the MnO₂/C composite material are the potential alternative materials as electrodes for applications in supercapacitors with excellent electrochemical properties.In this paper,the electrode materials were prepared by combining carbon-based material and different crystal type MnO₂.These MnO₂/C composite materials were further applied for fabrication of flexible supercapacitors,and their electrochemical properties were investigated as well.1.A facile method had been developed to grow MnO₂ nanoparticles on hybrid carbon nanofibers（MnO₂/HCNFs）for flexible supercapacitors.In this method,MnO₂nanoparticles was grown on hybrid carbon nanofibers by hydronthermal route.The hybrid carbon nanofibers（HCNFs）that consisted of CoO and graphene oxide（GO）were served as the buffer layer to improve the conductivity of MnO₂ and enhance the interface contact between MnO₂ and carbon nanofibers.The flexible supercapacitor based on MnO₂/HCNFs hybrid structure exhibited good electrochemical performance,extraordinary flexibility and superior cycle lifetime.Specific capacitance of the flexible supercapacitor reached at 295.1 F g^-1 under the scan rate at 0.5 A g^-1.Maximum specific energy（power）density was 20.1 Wh kg^-1(230.4 W kg^-1).Furthermore,the flexible supercapacitor exhibited high cycle life and low change in capacitance under dynamic bending.2.The MnO₂ and reduced graphene oxide（MnO₂/RGO）hybrid films were prepared by a simple and facile filtration deposition technique.The as-prepared hybrid film electrode exhibited a high specific capacitance of 333.9 F g^-1 at the current density of 0.5 A g^-1.The obtained hybrid films were further used as electrode materials for fabrication of flexible and sandwich type solid-state-symmetrical supercapacitor.The fabricated device displayed a maximum energy density of 23.5 Wh kg^-1 at the current density of 0.5 A g^-1 and power density of 1716.9 W kg^-1 at the current density of 2.25A g^-1.Meanwhile,the flexible supercapacitor showed excellent capacitance retention of 87%after 3,000 cycles.3.The negative electrode materials are crucial to improve electrochemical performance in asymmetric supercapacitors（ASCs）as well as positive electrode.Herein,theα-MnO₂/Ag/RGO hybrid films were prepared by a facile and rapid natural deposition technique and exhibited good electrochemical performance with specific capacitance of 804.6 F g^-1 at 1 A g^-1.The ASCs were further fabricated using NiCoS₂/CNFs andα-MnO₂/Ag/RGO film as positive and negative electrodes,respectively.The fabricated ASCs displayed the maximum energy density of 44.2 Wh kg^-1 at a power density of 288.2 W kg^-1.