Synthesis Of Micro/Nanostructured Transition Metal Oxides And Their Improved Performance As Anode Materials For Lithium Ion Batteries

Transition metal oxides as anode materials for lithium-ion batteries have a high theoretical specific capacity, but the large volume change and poor electronic conductivity have seriously hindered their practical applications. It is generally believed that coating with carbon layer is an effective way to improve their electrochemical properties, because the carbon coatings not only can strengthen the electronic conductivity, but also effectively prevent the pulverization originated from the volume change during the charge/discharge process. In addition, the preparation of nanomaterials with special morphology and porous structure can also effectively improve the electrochemical performance of lithium battery. The porous structure can provide a large contact area between the electrolyte and the electrode and limit the volume expansion during the charging and discharging processes. 1D nanostructure can supply 1D Li+ and electron transport pathways and high surface-to-volume ratio, which can not only improve electronic conductivity, but also enlarge the contact area between the electrode and electrolyte. 2D structures can provide desirable frameworks for fast lithium storage and shorten path for lithium ion intercalation/deintercalation. In this paper, we overcome the above shortcomings by carbon coating, preparation of nano-materials with special morphology and porous structure.1) ZnO@C nanospheres have been synthesized through a one-step co-pyrolysis method. The electrochemical properties of the ZnO@C nanospheres as an anode material are examined. The ZnO@C nanospheres give a reversible capacity of 440 mAh g^-1 at a current density of 100 mA g^-1 after 50 cycles, and the electrode represents a stable cycling performance with high coulombic efficiency?greater than 98%?.2) Leaf-like Cu O with mesoporous structure has been synthesized by treating commercial Cu?OH?2 powder at room temperature for an appropriate time. The electrochemical performances of leaf-like mesoporous CuO are evaluated by cyclic voltammetry and galvanostatic charge-discharge studies. Electrochemical results show that the as-prepared CuO electrode has excellent electrochemical properties, such as high reversible capacity(694.7 mAh g^-1 at 500 mAh g^-1), stable capacity retention?99.3% in 300 cycles?,even at the high current density of 2000 mA g^-1, the mesoporous CuO electrode still can maintain a specific capacity of 490.5 mAh g^-1, which is much higher than the theoretical specific capacity of graphite(372 mAh g^-1).3) Porous ZnMn₂O₄ nanowires were synthesized through a hydrothermal reaction and followed by a calcination process. The structure analyses indicated that the porous ZnMn₂O₄ nanowires assembled by many tiny nanoparticles. As expected, the sample showed excellent electrochemical properties in term of high specific capacity, long cyclic stability and good rate capability. It maintained a high reversible capacity of 869.5 mAh g^-1 at the current density of 500 mA g^-1 after 100 cycles. Even at high current of 4000 mA g^-1, it still delivered a specific capacity of 345.4 mAh g^-1, which is close to the theoretical capacity of graphite.