Nanostructural Construction Of Several Metal And Metal Oxide-based Electrode Materials And Their Electrochemical Properties

In order to cope with the increasingly serious energy crisis and environmental pollution problems,the demand for the energy stroage secondary batteries is increasing which requests high demand for the performances of the batteries.The exploring for electrode materials with high capacity,long cycle life and good stability depends on the construction and regulating of the material structures.The goal of this essay is to explore the structure construction of the electorde materials and their electrochemical properities,and thus we explore favorable approaches to synthesize materials with favorable morphologies and structures and analyzing their properities when used in lithium ion batteries and aqueous batteries.Fe3O4,Sn and MnO2 were selected as the representative materials for the conversion mechanism,alloy mechanism and insertion mechanism,respectively.We constructed various nanostructures via nanoconstruction and carbon composition of those materials and investigated their electorchemical performances and the corresponding sturcture-property relationships.The specific content is as follows:1.Fe3O4 nanoflakes in N-doped carbon matrix(Fe3O4 F@NC)were prepared via solvothermal syntheis of Fe3O4 nano flakes and in-situ polymerization of pyrrole on the surface of Fe3O4 by using sodium dodecyl sulfonate as surfactant and ammonium persulfate as oxidant followed by heat treatment.Compared to composite of Fe3O4 nanoparticles in N-doped carbon matrix,the Fe3O4 F@NC exhibit better electrochemical performances.Besides,the carbon content of Fe304 F@NC composites varies from 18%to 50%by controling the amount of pyrrole added at first,and the composite with 44%carbon content has the best electrochemical performances.The composite shows a reversible capacity of more than 1000 mAh g-1 after 200 cycles at 02 C and of 662 mAh g-1 after 500 cycles at 1 C.At the high rate of 5 C,the composite can still shows a capacity of 600 mAh g-1 after 200 cycles,exhibiting nice cycling and rate performances.The predominant performance of the Fe3O4 F@NC can be attributed to the combination of the 2D nano flake structure of Fe3O4 and the N-doped carbon matrix.2.We synthesis Sn-contained N-doped carbon composite(Sn@NC)with Sn nanoparticles of 5-30 nm uniformly dispersed in N-doped hollow carbon nanospheres,in which pyrrole serves as carbon source with N-doping and SnO2 nanopheres serve as Sn source and the self-sacrifice template.During the process,the SnO2@Ppy core-shell structure was formed at first.Under the heat treatment at 700?,the decomposition of Ppy to N-doped carbon and the reduction from SnO2 to Sn were simultaneously completed.Molten Sn dispersed uniformly into the hollow carbon nanospheres due to its low melting point.The obtained Sn@NC hollow nanospheres have an outer diameter of 80-100 nm and an inner diameter of 50 um.When used as anode for lithium ion batteries,the Sn@NC exhibits excellent electrochemical performances with a capacity of 1070 mAh g-1 at 0.2 C after 200 cycles,of 929 mA h g-1 at 1 C after 400 cycles and 500 mA h g-1 at 5 C after 500 cycles.These nice performances can be attributed to the combined effect of uniformly dispersed Sn nanoparticles and the N-doped hollow carbon nanospheres.Besides,we investigated the possible reasons for the capacity rising during cycling.The formation/decomposition of gel-like polymer during cycling and the increasing pseudo-capacitive behavior of the electrode maybe account for the rising capacity.3.The 2D ?-MnO2 composed of wrinkled nanosheets with a thickness of 2 nm and an average lateral dimension of about 200 nm was synthesized via the in-situ hydrothermal reduction of KMnO4 using graphene oxide as both reductant and self-sacrificing template.When used as cathode of the aqueous zinc ion batteries,the 8-MnO2 nanosheets exhibit shorter activation time,higher capacity and better cycling stability compared to the ?-MnO2 microspheres.The ?-MnO2 nanosheets show a reversible capacity of 133 mAh g-1 and 100 mAh g-1 after 100 cycles at a current density of 100 mA g-1 and 200 mA g-1.Besides,the charge/discharge mechanism has been studied.It's found by XRD analysis that the interlayer space of?-MnO2 is enlarged to 1.053 nm from original 0.719 nm in the discharge process?...