Controlled Synthesis And Lithium-storage Properties Of Three-dimensional Cobalt-based Transition Metal Oxide Nanowire Arrays

Lithium-ion batteries are the most popular novel energy devices among the electrochemical energy storage systems,while their energy densities and power densities still need to be improved.And compared with the cathodes,anodes own more space for enhancing the important factor—capacities for the above two parameters,hence attract a great deal of attention.The commercially used micro-bulk anode materials due to their restricted electrode kinetics and mass transport are approaching the limits of their performances now,thus,the nanosized structures are introduced into the design of anode materials with the expectation obtaining higher specific capacities.The attendence of nanosized electrodes can enhance the process of electrode kinetics and mass transport by shortening the length of ion diffusion and electron transport,can induce some new lithium-storage mechanisms such as electrical double-layer capacitance and faradic pseudocapacitance,can stablize the crystal structures of electrode materials.Of course,the better kinetic activities can not avoid the poorer thermodynamic stabilities,owing to that,the nanosized eletrodes depend on the temperature so much that trend to agglomerate more easily.Furthermore,the high side reactions on the surfaces engendered by the high specific surface areas of nanosized electrodes,dramatically decrease the coulombic efficiencies even cause some issues about safeties.Besides,the organic binders are necessary for integrating nano particles and connecting the nanosized electrodes and current collectors,and the introductions of those electrical insulators will drastically hinder the conductivities of electrodes and the interphase processes between electrodes and current collectors.Concerning the former two problems,the micro/nano hierarchical structures and carbon coating are proposed and applied.To have the organic binders absent,the self-supporting structures growing directly on the current collectors are introduced.Herein,in light of the high theoretical capacity（890 mAh/g）of cobalt oxide（Co₃O₄）and its spinel structure to form the pathways for lithium transportation,the nanosized structures of Co₃O₄ are achived via hydrothermal reactions on the matrixes copper foams with 3D net structures.However,as the transition metal oxides,its large volume expansion can not be overlooked,which will create worse cyclic stability.In this work,both the carbon coating and nickle/manganese replacements to exhbit binary materials can function as the two methods to resolve that issue and have gained desirable effects respectively.With carbon coating,the specific capacity of 3D Co₃O₄ nanowire arrays can reach 1484 mAh/g in 100 th cycle and the capacity retention can maintain 100%.And the nickle/ manganese replacements also can get better specific capacities and better stabilities while the difference of stability between those two still exists（MnCo₂O₄ performs better than NiCo₂O₄）,which is determined by the distinct tendencies of nickle/ manganese to occupy the A/B site of spinel structures.