Preparation And Electrochemical Properties Of Porous Manganese Oxide(MnO_x)-graphene Composites

Due to environmental degradation and fossil fuels consumption,rapid growth in renewable resources from sun and wind,as well as the development of renewable energy storage devices are urgent.The supercapacitor?SC?and lithium ion battery?LIB?as new energy storage devices have attracted much investigation.Manganese oxide?MnO_X?are outstanding candidates for both SC and LIB for their low cost,environmental friendiness,and high theoretical capacity.Manganese oxide?MnO_X?with mesoporous structure usually exhibits enhanced electrochemical performance compared with bulk materials.However,due to their poor electrical conductivity,the optimization of structure has some limitations for improving their capacity and rate performance.Graphene,with high electrical conductivity,large specific surface area and stable electrochemical property,is considered as an ideal additive to improve the electrochemical performance of MnO_X.Herein,in this paper,we prepared and researched the porous Mn₃O₄,Mn₅O₈,Mn₂O₃,finally synthesized the porous Mn₃O₄/reduced graphene oxid?rGO?with excellent double electrochemical performance?SC and LIB?.1)3D network mesoporous Mn₃O₄ with high specific surface areas have been successfully synthesized at room temperature by a template-free method.As a supercapacitor electrode,the sponge-like mesoporous Mn₃O₄ exhibit excellent comprehensive electrochemical properties,high specific capacitances(230²80 F g^-1at 0.5Ag^-1),as well as greatly improved rate and cycling performance in 1 M Na₂SO₄electrolyte.The capacitance retentions are >52.8% as the current density increasing from 0.5 Ag^-1 to 30 Ag^-1 with a cycle stability of >99% after 5000 cycles at a current density of 2 Ag^-1.2)The relationships between microstructures and electrochemical properties of 3D network mesoporous MnO_X?Mn₃O₄,Mn₅O₈,Mn₂O₃?were studied.These results showed that the compositions and morphology structures of manganese oxide are the key factors to the electrochemical performance,and electrode materials with larger specific surface areas,smaller particle sizes and better crystalline will exhibit improved electrochemical performance.3)3D network porous Mn₃O₄/rGO composites with excellent double electrochemical performance?SC and LIB?were prepared by controlling the graphene contents.The results indicate that as-prepared composite with 2.6%graphene content shows the best capacitive performance with high specific capacitances(315 F g^-1 at 0.5 Ag^-1),rate capability(69.5%at 30 Ag^-1)and an excellent cycle stability of 106.6%after 5000 cycles at a current density of 5 Ag^-1.When the graphene content increases to 6.6%,as-prepared composite shows the best electrochemical properties as anode material in LIB with large reversible capacity(1523 mAh g^-1 at 50 mAg^-1,540 mAh g^-1 at 1 Ag^-1),and improved cyclic performance.These results not only indicate that as-prepared 3D network porous Mn₃O₄/rGO composites show great potential and promise as electrode materials in both SC and LIB,but also provide guidance to prepare electrode material with double electrochemical performance?SC and LIB?at the same time.