Preparation And Electrochemical Properties Of Nanometer Manganese Dioxide/Carbon Materials Composite Electrode Materials

Manganese dioxide(Mn O2) has shown versatile applications in primary batteries, secondary batteries, metal-air batteries, and pseudocapacitors due to their high activity, high abundance, low price, and environmental friendliness. But the ultra-low conductivity of Mn O2 limits the actual capacity in application. Nano-scale Mn O2 could provide large effective surface areas for electrode reactions, and the combination with high conductive carbon materials could improve the conductivity of this composite, achieving the electrode materials with perfect electrochemical properties.In the present work, electrode composite materials of nanoscale Mn O2 and carbon with ternary hybrid structure were prepared. Flexible thin-film alkaline Zinc-Mn O2(Zn-Mn O2) batteries based on carbon nanotube(CNT) were prepared without any binder. The electrochemical performance related to different composites was investigated. Several highlights were discussed as follows.Carbon spheres with the diameter of 250 nm were prepared by hydrothermal method. Based on the direct reaction between carbon and KMn O4, nanoscale Mn O2 was uniformly coated on the surface of carbon spheres, forming the core-shell structure of C sphere-Mn O2 with Mn O2 mass content of 95% finally. Then, carbon sphere-Mn O2 was modified by Poly Diallyldimethylammonium Chloride(PDDA) to make the surface own positive charge. According to electrostatic adsorption, carbon sphere-Mn O2 could uniformly adsorb a layer of carboxyl of carbon nanotube(CNT). The composite of C sphere-Mn O2-CNT(PDDA) with the CNT content of 20 wt% shows higher capacity and better rate performance comparing to pristine carbon sphere-Mn O2 and the composite material of C sphere-Mn O2-CNT(H2O), which was formed by dispersing C sphere-Mn O2 water solution into CNT dispersion by simple mix. The inner core structure of conductive carbon spheres enhanced the inner conductivity of this composite, and CNT network were adsorbed on the surface of Mn O2, improving the ultilization of Mn O2. This ternary compostie showed the high capacity, good rate capacity and the structure stability.Porous reduced graphene oxide(r GO) wrapped on core-shell nanostructure of CNT-nanoflowers Mn O2, which could effectively improve the surface and inner conductivity of the composites. Unlike pristine r GO, the porous r GO does not block the diffusion of electrolyte into the inner part of this composite, improving the utilization of Mn O2 in this composite electrode very well. As a result, the as-prepared CNT-Mn O2-porous r GO ternary hybrid material shows superior specific capacitance and rate performance to pristine CNT-Mn O2 nanocables and pristine r GO wrapped CNT-Mn O2 nanocables.Carbon nanotube(CNT) film with high conductivity and perfect flexibility was prepared from floating catalyst chemical vapor deposition(FCCVD) method. Based on this ideal flexible scaffold of CNT film, electrochemical active materials of nanoscale γ-Mn O2 and Zinc(Zn) were uniformly loaded on the surface of CNT. The resultant flexible composite film electrodes without any conductive fillers and polymer binders can be served as the film for the assembly of a flexible thin-film Zn-Mn O2 alkaline primary battery with the thickness lower than 1 mm. This flexible battery exhibited high specific capacity(225 m Ah·g-1 at 0.5 C) and excellent rate capacity(214 m Ah·g-1 at 4 C). What’s more, this battery owns good flexibility and structural stability. When the radius of curvature came to 2.5 cm, the specific capacity reached 268 m Ah·g-1 at 0.5 C. It may be due to the more full contact between the gel electrolyte and active materials, making this battery show better discharge property under bending condition.