Preparation And Ultracapacitance Properties Of Mn-base Metal Oxide Electrode Materials

Supercapacitors?SCs?are a new type of energy storage device between traditional capacitors and batteries.They have the advantages of large capacity,high power density,long cycle life,high charge and discharge efficiency,maintenance-free,economical and environmental protection.It has become a research hotspot in the world of new energy.However,low energy density and high cost are the main challenges for SCs,among which electrode materials are the most critical factors affecting the performance and production cost of SCs.Therefore,the development of low-cost,highly efficient and stable electrode materials is the key to making SCs widely used in energy storage and conversion.High conductivity and reasonable structure design are two key ways to improve the supercapacitance performance of electrode materials.Therefore,researchers are working on the development of various nanostructures that facilitate ion diffusion.Among them,the integrated nanostructure with open network and free pore can effectively prevent the possible aggregation of active materials in the process of electrochemical reaction,thus ensuring the high utilization rate of electrode materials.In this paper,Mn-based metal oxides were grown on two different growth substrates,carbon cloth?CC?and nickel foam?NF?,and their supercapacitance performance were studied.Detailed research is summarized as follows:1.A binder-free electrode of ultrafine MnO₂ nanowires grown on the carbon cloth?CC?were fabricated by simple hydrothermal method,exhibiting the interconnected network with weed-like morphological feature.The unique pore structure allows rapid electrolyte diffusion through its hollow/open framework and fast electron transfer though the carbon skeleton.As an electrode for supercapacitors,the ultrafine MnO₂ nanowires grown on the CC?ultrafine MnO₂ nanowires@CC?exhibit a high specific capacitance?1174.3 F/g at the moderate current density of 2 A/g?,excellent rate property?stabilize at 927 F/g as the current density increases to 40 A/g?,and good cycling stability?a negligible 0.1%decay in specific capacitances after10,000 cycles?.2.The 3D interconnected ultrathin MnMoO₄ nanosheets arrays with abundant open space and ordered arrangement grown on highly conductive Ni foam substrate?NF@MnMoO₄?by a one-step hydrothermal growth present fascinating advantages,such as exposing abundant electroactive sites,accelerating ion transport and charge transfer and improving the efficient of redox reactions.As integrated additive-free electrodes for supercapacitors,the optimized NF@MnMoO₄ electrode exhibits superhigh specific capacitance of 4609 F/g at current density of 1 A/g and maintains at 2800 F/g even at a high current density of 20 A/g.Meanwhile the NF@MnMoO₄ electrode shows the excellent cycle life with 92.4%capacitance retention after 20,000 cycles.3.The corresponding asymmetric supercapacitor assembled with NF@MnMoO₄ nanosheets arrays and active carbon as negative electrode and positive electrode,respectively,achieves a high energy density of 76.9 Wh kg-1 at a power density of 753.9 W kg-1 and exhibits excellent cycling stability?90.4%retention after 2,000 cycles?,which highlights its great potential in applications of high-performance asymmetric supercapacitor device.