Structure Design And Properties Of Core-Shell Composite Pseudocapacitor Electrode Materials Based On Ultralong Manganese Dioxide Nanowires

Manganese dioxide is one of the most promising supercapacitor pseudocapacitor electrodes.Its high theoretical specific capacity(1370 F g^-1),large specific surface area and low price have attracted great attention from researchers.Transition metal oxides/hydroxides generally have lower power density and poor cycle stability.Due to the poor conductivity of the transition metal oxides/hydroxides,the electron transfer rate is limited,resulting in a low power density.In addition,the cyclic stability of the electrode material is insufficient due to the morphology damage caused by expansion and contraction during charge and discharge.In this study,the electrochemical performance and cyclic stability of manganese dioxide were improved by interface regulation.A stable MnO₂nanowires@NiCo-LDH nanosheets core-shell heterostructure are synthesized by simple liquid-phase method,in which The Ni Co-LDH nanosheets grow uniformly on the surface of ultra-long MnO₂ nanowires with a stable tunnel structure.Electrochemical studies show that the core-shell electrode has a high specific capacitance of 708 C g^-1 at a current density of 1 A g^-1,and exhibits a capacitance retention.According to in-situ Raman spectral analysis,the Ni Co-LDH material in the core-shell structure electrode reveals a very slow transition from?to?phase in the cycle process compared to the pure Ni Co-LDH electrode,which can be attributed to the stable core-shell heterostructure buffering the collapse of the layered Ni Co-LDH nanosheets and slowing down the irreversible phase transition in the process of charging-discharing by the synergistic effect between one-dimensional nanowires and two-dimensional nanosheets.In order to further explore the energy storage mechanism of core-shell heterostructures of ultra-long nanowires,stable heterostructures of MnO₂ nanowires@NiMn bimetallic oxides with oxygen vacancy were synthesized by liquid phase synthesis and further heat treatment.Electrochemical study shows that the electrode has excellent cycle stability,and can achieve 94.9%capacitance retention when 10 A g^-1 cycles 20000 times(the specific capacitance is 463.5 C g^-1 when the current density is 1 A g^-1).Due to the potential synergistic effect between one-dimensional nanowires and two-dimensional nanosheets,the resulting nanosheet structure is conducive to surface active site exposure and electrolyte diffusion.The introduction of oxygen vacancy can significantly enhance the conductivity and electrochemical activity of the electrode material,which is help to improve the interaction between the metal oxide and hydroxyl ions in the electrolyte,so that the specific capacitance of the electrode material is increased,and the cycling stability is also significantly enhanced.