| A brief review of the investigation and development of the cathode and anode materials of lithium ion batteries (LIBs), especially for the copper oxides anode materials are conducted. According to the fact that copper foil is commonly used as the current collectors of anode, the present thesis aims to prepare copper oxides on copper foil by a simple, economic and practical method of thermal oxidation. The film of the copper oxides and the copper matrix can be used as anode directly, which is considered to save the fabrication process such as active material slurry preparation and coating, etc. The effects of the fabrication parameters including the oxidation temperatures, times, the thickness of the copper foil as well as its roughness and the electrochemical properties are investigated by X-ray diffraction, scanning electron microscope etc. and electrochemical testing of galvanostatic charge-discharge, cyclic voltammograms, etc. The key factors which affect the cycle stability, initial irreversible as well as high-rate capability of the film anode and their mechanism are also discussed. In addition, effect of the coating of conductive acetylene black on the electrochemical properties of the film anode is also studied.The results show that the oxidation temperature plays important role in the phase structure of the oxides. The oxide obtained at 250℃is single CU2O, while they are CuoO and CuO as the oxidation temperature is over 300℃. The content of the oxides is increased with the oxidation temperature. The content of the oxides is influenced certainly by the oxidation times, showing an increase with the oxidation times. Electrochemical testing shows that the copper oxide film anode obtained at the oxidation temperature range of 250-350℃show superior cycle stability, which is attributed to the excellent combination of the copper oxide film and the copper matrix, which has high conductivity and high toughness.. The thicker thickness of the copper foil, which has higher deformation resistance, the larger surface roughness, which increases the boning strength of the oxide film and the matrix, the lower oxidation temperature and the shorter time, which lead to thin oxide layer, all result in higher capacity, better cycle stability and higher high-rate capability of the film anode.The investigation of the acetylene black coating on the surface oxide film can improve the electrochemical properties including the initial coulombic efficiency, the reversible capacity and the high-rate capability of the anode. The anode obtained at 350℃X 1 h shows increasing initial coulomblic efficiency from 20%to 26%after the surface coating of 0.27 mg/cm2 acetylene black. The discharge capacity after 100 cycles is increased by 88%, from 289 mAh/g to 542 mAh/g. The capacity at 5 C is increased from 121 mAh/g to 274 mAh/g. The effect of the acetylene black is much effective in improving the electrochemical properties of the anode with thinner oxidation layer. It is also much effective for the anode oxidized by higher temperature but shorter times in the cause of the amount of the oxidation layer is the same. However, with the cycling, the variation of the effect is decreased. But excessive content of acetylene black lowers the discharge capacity as acetylene black is less active for Li insertion and extraction compared with copper oxides. The concentration of the acetylene black slurry affect the electrochemical properties of the anode more evidently in the low discharge rate compared with in the high discharge rate.. The anode prepared by 300℃×4h shows capacities of 445,489 and 511 mAh/g after 60 cycles at 0.1 C, respectively, for the after the coating of 0.27 mg/cm2 acetylene black from slurry with the ratio of 1:40,1:50 and 1:60 for acetylene black to N-methyl-2-pyrrolidone. At the high rate of 5 C and 20 C, the anode coating by slurry with different concentration show close discharge capacity, being 190 and 100 mAh/g. respectively. The anode shows favorable high-rate capability. |
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