Preparation Of Manganese-based Oxide Nanomaterials And Its Application In Supercapacitors

Manganese-based oxides have the advantages of low cost,environmental friendliness and large theoretical capacitance,et,al.Therefore,they can be used as supercapacitor electrode(SC)materials to obtain ideal SC devices.However,due to their poor conductivity and wide bandgap,it is difficult to obtain good electrochemical performance in practical applications.In order to improve the electrochemical performance of manganese-based oxides,different manganese oxides have been synthesized by preparing manganese oxides with a special structure,recombination with r GO,synthesis of ternary metal oxides and so on.The main research includes:(1)Ultrafine Mn₃O₄ nanowires with an average diameter of 4.0 nm were synthesized using a direct precipitation method.They also show a large pore volume of 0.7960 cm~3g^-1,which can provide essential channels for ion transport during charging and discharging processes.The supercapacitor electrode made of these ultrafine Mn₃O₄nanowires exhibits a predominant surface capacitive behavior during charge/discharge processes and achieves a large specific capacitance of 433.1 F g^-1 at a current density of0.5 A g^-1 with a very wide voltage range from-0.5 V to 1.1 V in 1 M Na₂SO₄ electrolyte.An asymmetric supercapacitor(ASC)was assembled using a positive electrode made of these ultrafine Mn₃O₄ nanowires and an active carbon(AC)negative electrode,and a high energy density of 26.68 Wh kg^-1 at a power density of 442 W kg^-1 was achieved.The ASC showed a good cycling stability,and its capacitance value was still maintained at 75.8%after 64000 charge/discharge cycles,which can be putted into practical application.(2)The ultrafine Mn₂O₃/rGO composites were synthesized using a direct precipitation method,and the effects of different amounts of r GO on the electrochemical properties of Mn₂O₃ were compared.In a 2 M KOH electrolyte,the Mn₂O₃/r GO electrode has the best electrochemical performance when the amount of r GO is 2%wt.The specific capacitance of Mn₂O₃/r GO is 782 F g^-1 at the current density of 1 A g^-1.An ASC was assembled using the Mn₂O₃/r GO-2 electrode as the positive electrode and an AC electrode as the negative electrode.The energy density of the ASC is 28.6 Wh kg^-1 at a power density of 373.8 W kg^-1.After 64,000 charge and discharge cycles,the capacitance of the ASC can maintain 97.4%of its original capacitance,showing excellent cycling performance,has a good development prospect.(3)Mn Co₂O₄/Ni₃S₄ nanocomposite was synthesized using a two-step hydrothermal process.Compared with individual Mn Co₂O₄ and Ni₃S₄,the Mn Co₂O₄/Ni₃S₄nanocomposite showed a higher specific capacity and a better cycling stability as the electrode for the supercapacitor.The specific capacity value of the Mn Co₂O₄/Ni₃S₄electrode was 1644.9 F g^-1 at 1 A g^-1 with a potential window of 0?0.55 V.An ASC was assembled using Mn Co₂O₄/Ni₃S₄ and active carbon as the positive and negative,respectively,showed a capacitance of 116.4 F g^-1 at 1 A g^-1,and a high energy density of50.7 Wh kg^-1 at 405.8 W kg^-1.Long-term electrochemical stability tests showed an obvious increase of the ASC's capacitance after 5500 charge/discharge cycles,reached a maximum value of?162.7%of its initial value after 25000 cycles,and then remained a stable value up to 64000 cycles.Simultaneously,its energy density was increased to 54.2Wh kg^-1 after 64000 cycles,which has a high application value.