| Summary: | 碩士 === 逢甲大學 === 材料科學所 === 93 === Abstract
Recently, Lithium ion secondary batteries have been of great interest to us. They are used as a portable energy source, particularly for lightweight, compact 3C electronics. Because of its high capacity, stable working voltage, superior energy density, low self-discharge rate, and long cycle life, it will become the most popular type of the rechargeable battery in the future, and replace the other competitors.
LiNi0.8Co0.2O2 is a potential cathode material which has high ideal capacity and is cheaper than LiCoO2 (commerciallized cathode material). In this research, lithium nickel cobalt oxide (LiNi0.8Co0.2O2) was used as cathode material for the thin film batteries (TFBs).
In the experiments, lithium nickelate (Li-Ni-O) thin films was prepared by an inductively coupled plasma (ICP) assisted sputtering technique. Since it is a low-temperature process, various substrate materials can be used. It is an advantage over traditional in-situ heat treatments, which limit the choice of substrates. By this process, in-situ modification of the film texture can be achieved.
In addition, Langmuir probe method was applied to study the characteristics of the plasma with the ICP process. The ICP deposition was carried out using a magnetron sputtering gun with a lithium nickel cobalt oxide (LiNi0.8Co0.2O2) and lithium cobalt oxide(LiCoO2) target at different pressures (pure Ar) on Silicon oxide (SiO2) substrate and to deposit two films of LiNi0.8Co0.2O2 and LiCoO2 .
The main process variables are deposition temperature, rf powers of the substrates. ICP technique could provide higher ion flux than traditional method. The properties of nickel cobalt oxide and lithium cobalt oxide thin films were studied under different bombarding situations.
Film texture and crystallity were characterized by X-ray Diffractometer (XRD) and Charge-discharge measurements were carried out by Auto lab potentio state.
For lithium cobalt oxide(LiCoO2), the temperature of Atmosphere annealing from 600℃decreased down to 350℃ of in-situ heating ,and the capacity of coin cell is 70 mAh/g above three Voltage of cell. Because the formation of (101) and (104) crystalline is favorable for the transmission of lithium ion. And the energy of heat was instead by the ion of plasma to provide to the film growth. It is the great modification in this stuty. Integrating the plasma modification and in-situ heating of 350℃ can successfully upgrade the capacity of LiNi0.8Co0.2O2 to 160 mAh/g above 1.5 voltage.
Keyword：LiNi0.8Co0.2O2, LiCoO2,Inductively coupled plasma, thin film electrode
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