Fabrication And Electrochemical Studies Of Manganese Oxides Composite Electrode As Anode For Lithium Ion Battery

As one of the most promising anode materials for lithium-ion batteries,manganese oxides have attracted broad attention because of their high theoretical specific capacity,abundant resource,low cost and environmental friendliness.But the noticeable drawbacks of manganese oxides as anode impede their commercial utilization:(1)manganese oxides undergo huge volume change during the cycling process which will destroy the electrode structure leading to continuous decline of capacity;(2)their low intrinsic electrical conductivity results in unsatisfactory electrochemical performance under high current density.In order to solve the above problems,researchers are devoted to synthesizing manganese oxides nanoparticles or compounding them with carbonaceous materials.However,in addition to the intrinsic shortcomings of manganese oxides,the prevailing fabrication of electrode,coating method,also has imperfection.Not only does the using of polymer binder during the coating process reduce the energy density,but also has negative effect on the electrical conductivity of the electrode.Therefore,considering the mentioned factors,we adopt electrophoretic deposition method to prepare binder-free electrode,composed of manganese oxides and different carbon materials,as anode for lithium-ion battery.(1)MnO2 nanowire,prepared through the hydrothermal process,is co-deposited with acetylene black,carbon nanotubes and graphene oxides onto the copper foil,respectively.After a heat treatment,three kinds of composite electrode are obtained.Because of the introduction of different carbon materials,three kinds of composite electrode possess various electrode structures.The particles of acetylene black cluster around the manganese oxides nanowires,which could not only enhance the electrical conductivity of the electrode,but also provides the buffer space for the volume change of manganese oxides during the cycling process.Carbon nanotubes and manganese oxides nanowires are tightly interwoven to construct a nest-like architecture.This nest-like structure exhibits the excellent cycling stability.At the same time,the crosslinking carbon nanotubes can build an extensive electron conductive network to improve the electrical conductivity.The reduced graphene oxides either serve as carriers to support the manganese oxides nanowires or insert into the crowds of manganese oxides nanowires.The cycling performances of three kinds of electrode are tested as anode in the coin cells,compared with the MnO and Mn3O4 electrodes prepared by traditional coating method.(2)In order to simplify the preparation procedure of manganese dioxide,commercial electrolytic MnO2 subjected to ball-milling process is used as starting material.The ball-milling MnO2 is co-deposited with acetylene black,carbon nanotubes and graphene oxides on the copper foil through the electrophoretic deposition method.After heat treatment under Ar atmosphere,three kinds of composite electrode with different structures are acquired.In the composite electrode containing acetylene black,the ball-milling manganese oxides are dispersed into nanoparticles.These nanoparticles of manganese oxides mix with the same-size acetylene black particles to construct a porous electrode.In the composite electrode containing carbon nanotubes,the tubular carbon materials interwine with the manganese oxides nanoparticles to build a stable electrode structure.Furthermore,carbon nanotubes also construct a large-scale electron conductive network to significantly improve the electrical conductivity.In the composite electrode containing reduced graphene oxides,the ball-milling manganese oxides still maintain the bulk morphology instead of being dispersed into nanoparticles.The reduced graphene oxides either serve as carriers to support the bulk-like manganese oxides or insert into the crowds of manganese oxides.These three kinds of electrode exhibit different cycling performances.