Preparation And Supercapacitive Performance Of Flexible Composite Film Based On ?-MnO₂ Nanowires

As a new type of electrochemical storage device,supercapacitors have higher energy density than traditional parallel plate capacitors,and higher power density and long lifespan than lithium-ion batteries.Manganese dioxide(MnO₂),as a typical pseudocapacitive material,has advantages of high specific capacitance,low-cost and environmental compatibility.However,its poor electrical conductivity greatly limits its application in supercapacitor field.Nanocarbon materials have high specific surface,outstanding electrical conductivity,and good mechanical properties.Herein,combination low-dimensional nanocarbon materials with MnO₂ could synergically exploit both advantages.The?-MnO₂NW_S/NRGO/MWCNT composite films were prepared via vacuum filtrating the mixed dispersion of as-synthesized MnO₂ nanowires,amino-modified reduced graphene oxide(NRGO)and multi-wall carbon nanotubes(MWCNT).The structure features were characterized,and electrochemical properties were studied to achieve the results as follows:(1)One-dimensional?-MnO₂ nanowires(?-MnO₂ NW_S)with good dispersivity and large aspect ratio were prepared by a one-step hydrothermal method.Then,?-MnO₂NW_S/NRGO composite film was prepared by vacuum-filtrating the mixed dispersion of?-MnO₂ NW_S and NRGO.Comprehensive characterization and electrochemical test results show that ?-MnO₂ NW_S/NRGO composite film present a dense network structure.Such?-MnO₂ NW_S/NRGO film electrode delivers an areal specific capacitance of 386.8 m F cm^-2 at the current density of 1 m A cm^-2,and retains 62.4%capacitance at 10 m A·cm^-2.(2)Flexible?-MnO₂NW_S/NRGO/MWCNT composite film was prepared via vacuum-filtrating the mixed dispersion of as-synthesized?-MnO₂NW_S,NRGO and MWCNT at a certain mass ratio.Comprehensive characterization and electrochemical test results show that:?-MnO₂NW_S/NRGO/MWCNT-8 film electrode(8 wt%MWCNT)delivers an areal specific capacitance of 495.7 mF·cm^-2 at the current density of 1 m A·cm^-2 with 69%capacitance retention at the current density of 10 m A·cm^-2.The tensile strength of film electrode is 2.41 MPa with elongation of 1.32%.Introduction of MWCNT further increase the conductivity and mechanical properties of?-MnO₂NW_S/NRGO/MWCNT film electrode,and meanwhile?-MnO₂NW_S and MWCNT could help to prevent stacking of graphene nanosheets.(3)Flexible symmetric supercapacitor device was assembled using as-prepared?-MnO₂NW_S/NRGO/MWCNT composite film as both positive and negative electrodes.The specific capacitance of assembled device reaches 365 m F cm^-2 at current density of 2 m A cm^-2,and the capacitance retention and Coulomb efficiency are respectively93% and 99% after 4000 cycles at 10 mA cm^-2.