Reactive sputtering of LiFePO4-xNy

• Main Authors: Yuan-Ruei Jheng, 鄭元瑞
• Other Authors: Kuo-Feng Chiu
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/35450119904270968767

碩士 === 逢甲大學 === 材料科學與工程學系 === 101 === Rechargeable lithium ion batteries have emerged as one of the important power sources for various mobile devices such as cellular phones, cameras, and notebook computers due to high energy density and excellent cyclic performance. In order to reduce weights and volumes for mobile devices, the demands of lighter and thinner batteries are increasing. As the sizes of batteries are scaled down to micrometer/nanometer rang, the concept of thin film batteries have become inevitable. Lithium ion batteries has been commercialized for a long time. It can be observed that lithium ion batteries was lively used in mobile phone and notebook. The cathode materials for these lithium ion batteries is usually used LiCoO2 due to its stable electrochemical performance, simply process. Therefore, it is good choice to used LiCoO2 for the cathode of lithium ion batteries. However, because Co is expensive and unfriendly to environment, many researchers were used the other materials to replace LiCoO2. LiFePO4 is a popular cathode materials for lithium ion batteries due to good electrochemical performances, low cost, high safety. However, it is nearly an electronic insulator with conductivity as low as 10−9 Scm−1, and also shows low Li ion transport rate over the LiFePO4/FePO4 two-phase boundary during the charge-discharge process. By improving the preparation processes, the electrochemical properties of LiFePO4 can be enhanced. Recently, many researchers have been demonstrated that improvement of LiFePO4 electronic conductivity, such as coating carbon and doping transition metal. Lithium iron phosphate (LiFePO4) thin films have been synthesized by reactive magnetron sputter deposition process. In order to increase the conductivity of LiFePO4 thin films, nitrogen gas has been introduced during deposition, which results in nitrogen doping of LiFePO4 thin films. The LiFePO4-xNy thin films deposited under various nitrogen/argon ratios were characterized. The surface morphology and microstructures of as-deposited thin films were observed by scanning electron microscope (FESEM). The film crystallography and electronic conductivity was characterized by grazing angle X-ray diffraction (XRD) , Raman spectroscopy and four point probe. And confirmed by X-ray Photoelectron Spectrum and Fourier transform infrared spectroscopy nitrogen have successfully doped into LiFePO4. The results showed that the conductivity of the LiFePO4 thin films have been significantly improved by nitrogen doping. Under optimal condition, the LiFePO4-xNy thin films are able to sustain a current density as high as A/g (45 C-rate) during charge-discharge process, and Discharge plateau can be maintained over 3.2V. The capacity at A/g (10 C-rate) is higher than 100 mAh/g. All of these results nitrogen-doped can improve the electrochemical performance of LiFePO4 films.