Fabrication Of Mixed Transitional Oxide Nanomaterials And Their Applications In Lithium-ion Battery

Metal oxides have long been considered as promising anode materials for lithium-ion batteries (LIB) to improve the graphite anode, because they could gain much higher specific capacity and power density compared with the graphite-based anode. The metal oxides reactions with Li do not via the classical insertion/deinsertion process:the reactions involve in two different mechanisms:one type is based on a Li-alloying/dealloying process; another type involves a displacive phase transition. The typical materials of the first type are Sn, Zn, In and Sb oxides; the oxides irreversibly deoxidized to metal, then the metal could reversibly alloy with lithium to uptake one or more lithium per metal atom. Take SnO2for instance, the reactions routes are SnO2+4Liâ†'Sn+2Li2O, and mSn+nLi(?)LinSnm. The oxides of the second type include Co3O4, NiO, Fe2O3and so on; the reaction process with Li contains the reversibly reduction of the oxide, then the formation and decomposition of Li2O matrix, along with the reduction and oxidation of metal. These oxides could achieve quite high reversible capacity due to the multi-electron redox process; in this case, the specific capacity depends on the oxidation state of the transition metal participate in the reaction. The general equation of conversion reaction is described as MxO+2Li++2e-(?)xM0+Li2O.However, there are several drawbacks preventing the transitional-based anodes from being commercial uses, such as the low energy efficiency during the first discharge process large volume changes and poor capacity retention. To overcome these obstacles, intensive researches like tailoring metal oxides materials to the nanoscale, forming nanocomposites with carbon materials and graphene, and doping with novel metal particles have been conducted. Recently, fabricating nanosized mixed metal oxide compounds with superior capability becomes a new strategy to improve the performance. In this paper, we fabricated binary metal oxides like ZnFe2O4, CuFe2O4and Mn WO4to research their electrochemical performance.Regular ZnFe2O4octahedrons with an average size of200nm have been synthesized through a one step hydrothermal method by zinc acetate and ferrous chloride. XRD, SEM and HRTEM studies reveal that the products are highly crystallized and uniformly enclosed by{111} facet. Galvanostatic cycling lithium battery anode at60mA·g-1between0.01and3.0V up to80cycles exhibits a high capacity of910mAh·g-1. The ZnFeO4octahedrons also exhibit an excellent rate performance, and deliver stable reversible specific capacity of730inAh·g-1even after300cycles at1000mA·g-1. The reaction mechanism for Li-recyclability is proposed based on the ex-situ HRTEM and SAED analysis of the electrodes after completely discharged and charged together with voltage profile and cyclic voltammetry. The lithium-driven structural reorganization and plasticity deformation of electrode materials are observed and discussed specifically.Cubic CuFe2O4(c-CuFe2O4and tetragonal CuFe2O4(t-CuFe2O4) nanoparticles were selectively prepared using a facile one-step solid state reaction route by ferrous oxalate and copper acetate as the reactants. As an anode material for Li-ion batteries, the electrode reactions of the two phases CuFe2O4are similar except the lithium insertion process during the first discharge; the preceding Lithium intercalation occurred and formed intermediate phase LixCuFe2O4when c-CuFe2O4was applied as anode material, but this intermediate phase is hardly observed in the t-CuFe2O4. Compared with c-CuFe2O4and t-CuFe2O4synthesized at800℃, c-CuFe2O4synthesized at400℃with larger surface area exhibited superior discharge capacities with good cycling performance (950mAh·g-1at100mA·g-1after60cycles), and higher rate capability. Through ex-situ HRTEM analysis, we observed the existence of metastable FexCu1-x alloy in the discharged nanocomposition for the first time, which exhibits the interaction of metallic Cu particles with the adjacent iron ions.The MnWO4nanobars with dense nanocavities have been synthesized through hydrothermal route; the average particle size of the MnW04nanobars is about20-30nm, and the nanocavities inside are about5-8nm. Galvanostatic cycling of MnWO4lithium battery anode exhibit an excellent rate performance. The improved electrochemical performance could be attributed to the unique geometry nanocavities and improved accommodation of the transformation strains during cycling.These works resulted in convenient methods for obtaining mixed metal oxide nanomaterials, and provided an opportunity to further application of these promising materials with the remarkable performance, both in terms of long life span and rate capability.