Synthesis And Energy Storage Characterization Of Nanoflaky Nickel Cobalt Manganese Oxide Composites

Recently, some transition metal oxides(TMOs) have been considered to be promising anode materials for supercapacitors and LIBs owing to their high theoretical capacity, low cost, natural abundance and environmental friendliness. However, it is still a challenge to achieve high energy density for supercapacitors due to the low conductivity and low diffusion coefficiency of inserted cations. Currently, extensive researches should be done to solve these problems.In this paper, to address to the poor conductivity of MnO2, a facile hydrothermal method has been designed to synthesize flower texture carbon microbead(CMB) @MnO2with the CMB core and the MnO2 shell via an in situ nucleation and growth of birnessite-type MnO2 on the surface of monodisperse carbon microbead. The diamanter of the composites is about 1.5μm. As the anode material for lithium-ion batteries, the CMB@MnO2 nanocomposite exhibits excellent electrochemical performances. It shows a good rate capability of 230 mAh g-1 at the current density of 1500 mA g-1 and a large reversible capacity of 620 mAh g-1 without capacity fade for the 80 th cycles at 100 mA g-1.In addition, rational design of transition metal oxide composite can provide a promising solution to achieve excellent electrochemistry performance due to the synergistic effects of different components, which can effectively improve the electrochemical performances of the materials. Thus, three kinds of hierarchical mesoporous structure transition metal oxides, which are composed of a β-MnO2 nanorod core and one of three different nanosheet hybrid(Ni, Co, Mn) oxide shells, are facilely synthesized via a novel in situ nucleation and growth of transition metal oxides on the surface of the β-MnO2 nanorod. The crystallographic analyses demonstrated that the three kinds of hybrid oxide shells are consisted of cobalt manganese oxide(CMO), nickel manganese oxide(NMO), and nickel cobalt manganese oxide(NCMO), respectively. These transition metal oxides are evaluated as electrodes for high performance supercapacitors(SCs). The results reveal that β-MnO2@CMO exhibits still a good rate capability, while β-MnO2@NMO displays a high pseudocapacitance of 560 F g-1 at 1 A g-1. However, β-MnO2@NCMO combined the advantages of both β-MnO2@CMO and β-MnO2@NMO, exhibits a high specific capacitance of 675 F g-1 at 1 A g-1.Futhermore, synthesizing transition metal oxides with high specific surface area, which can provide more sites for reaction between the active materials and electrolyte ions, are considered to be a most promising method for preparing pseudocapacitors electrode materials. Thus, the nickel cobalt manganese oxide(NCMO/CNT) with hierarchical tubular nanoflaky structure is intentionally designed and synthesized via a facile method by using carbon nanotube(CNT) as a backbone template, then the nickel cobalt manganese oxide with nanosheet-like nanotube structure(NCMONST) is synthesized after removed successfully the CNT templates. The as-prepared NCMONST maintains the tubular and sheets-like structure of NCMO/CNT, and possesses a high specific surface area of 134.1 m2 g-1 and broad pore-size distribution. The electrochemical results show that the NCMONST exhibits a high specific capacitance of 680 F g-1 at 1 A g-1.