Preparation Of Nanoscale Transition Metal Oxides And Their Application Of Lithium-ion Batteries

Lithium ion batteries have been attarcted extensively attention in the past decades owing to their high power density and high energy density. However, most of the commercial anode materials are graphite-based materials which have a low theoretical specific capacity of372mA h g-1. Such a small capacity cannot meet the demand of high-energy applications (such as electric vehicles). Thus, alternative anode materials with high energy capability are urgent demanded. Transition metal oxides have been considered as promising alternative anode materials because of their high specific capacity (450～1500mA h g-1). Besides, transition metal oxides are also considered to be excellent catalyst. It is well known that nanoscale materials as anode materials or catalysts are more effective than the bulk ones. Therefore, we synthesized nano-level transition metal oxides to improve their lithium storage capacity and catalytic capacity.Branched MnOOH nanorods with diameters in the range of50to150nm and lengths up to tens of micrometers were prepared by using potassium permanganate (KMnO4) and PEG400as starting materials though a simple hydrothermal process at160℃. PEG400is a nonionic surfactant with uniform and ordered chain structure, it is easily adsorbed at the surface of metal oxide colloid during the synthesis, confining the colloid and facilitating anisotropic growth of the nanocrystals. With a prolonged reaction time, the diameters and lengths of these nanorods increased notably. To reduce the total interfacial energy of the system, large amounts of these nanorods tended to aggregate and grow into branched structures. Through tuning the experimental parameters such as the annealing atmosphere and temperature, β-MnO2, Mn2O3, mesoporous and nonmesoporoys Mn3O4, MnO and Mn5O8could be controllable produced. Among them, the mesoporous Mn3O4nanorods are good anode materials for li-ion batteries and efficient for the catalytic degradation of methylene blue (MB) in the presence of H2O2at80℃. The good performance of the mesoporous Mn3O4nanorods can be ascribed to the one-dimensional and mesoporous structures which allow for efficient contact area (electrode-electrolyte and reaction materials-catalyst) and excellent electron transport pathways.Spinel LiMn2O4nanorods were synthesized through a solid state reaction at700℃for10h by using MnOOH nanorods as the template which was obtained by a hydrothermal route. LiMn2O4nanorods have diameters of100-170nm and lengths of several micrometers. The synthesized LiMn2O4nanorods were characterized by FT-IR,XRD,TEM,SEM and HRTEM. Galvanostatic battery testing showed that the synthesized LiMn2O4nanorods can deliver high capacity and very good cycle stability (110and80mAh g-1at current rate1C and10C up to50cycles, respectively.) in the potential window of3.0-4.3V. Even at the current rate of20C, the capacity of67mAh g-1was still kept after500cycles. This result is the same as LiMnO4/CNTS composites. Such good performances may be attributed to the the favorable morphology and the raw material of MnOOH. In reaction process, MnOOH generated pore-like structure which was in favor of the reaction materials well mixed, and led to the reaction more completely. Furthermore, the synthesized LiMn2O4is a mixture of tetragonal and cubic phases which is benefit for the cycling proformance.We modified the reaction conditions, and still used (KMnO4) and PEG400as starting materials prepared MnOOH nanorods. After then, loaf-like ZnMn2O4nanorods with diameters of80-150nm and lengths of several micrometers were successfully synthesized by calcination of MnOOH nanorods and Zn(OH)2powders at700℃for2h. The electrochemical properties of the loaf-like ZnMn2O4nanorods were investigated to determine its reversible capacity, rate and cycling performance as the anode material for lithium ion batteries (LIBs). This loaf-like ZnMn2O4material exhibited excellent capacity retention, after100cycles, it still gave a capacity of517mAh g-1at a current density of500mA g-1, as well as enhanced rate capability. The improved electrochemical performance can be ascribed to the one-dimensional and hollow structure of the loaf-like ZnMn2O4nanorods which provided large surface-to-volume ratio that allows for efficient electrode-electrolyte contact and excellent one-dimensional electron transport pathways, and sufficient void space for buffering the volume variation during the Li+insertion/extraction. The reaction conditions and possible formation mechanism for the loaf-like ZnMn2O4nanorods were also discussed. The experimental results suggest that loaf-like ZnMn2O4nanorods synthesized by this method are promising anode material for LIBs. Besides, the reaction conditions for syntheses of loaf-like ZnMn2O4nanorods were investigated. And the possible mechanism for preparing the loaf-like ZnMn2O4nanorods was discussed.Urchin-like Fe3BO5@carbon core-shell structures (defined as "FBOC") have been fabricated by a one-step Co-pyrolysis method using boric acid and ferrocene as raw materials. This complex architecture is composed of high-density Fe3BO5@carbon nanocables that stand on Fe3BO5@carbon structure. After removing the Fe3BO5, hollow urchin-like carbon material was obtained. In the reaction process, B2O3and H2O that decomposed from H3BO3have synergistic effect on the formation of urchin-like structures. It is found that urchin-like structures can also be obtained when other materials that can release H2O and B2O3react with ferrocene. The influences of the reaction conditions on the preparation of FBOC have been discussed in detail.