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URN etd-0811116-153746 Statistics This thesis had been viewed 670 times. Download 101 times. Author Chieh-Han Chang Author's Email Address No Public. Department Chemical Engineering Year 2015 Semester 2 Degree Master Type of Document Master's Thesis Language zh-TW.Big5 Chinese Page Count 59 Title Fading Mechanism of Li(Ni0.5Mn0.3Co0.2)O2/MCMB Lithium Ion Battery Keyword NMC Fading A/C A/C Fading NMC Abstract Fading mechanism of Li(Ni0.5Mn0.3Co0.2)O2/MCMB lithium ion battery has been studied. Cells of three anode/cathode loading ratios (A/C ratio), 0.9, 1.1 and 1.3, were prepared and age-tested for 200 charge/discharge cycles at three c-rates, 0.2, 0.5 and 1.0C.
Experimental results show that with the increasing number of cycles, the capacity of charge and discharge decreases and the internal resistance of the cell increases. Results of incremental capacity analysis (ICA) show that the peaks of charge shift toward the higher voltage side with increasing number of cycles, due to the loss of movable lithium ion. The peaks of discharge shift to the lower voltage side, due that the impedance of the cell increases with increasing number of cycles.
At the same A/C ratio of 1.1, capacity fading increases with decreasing c-rate, while at the same c-rate of 1C, the cell with A/C ratio of 1.3 has the fastest fading rate, followed by that of 0.9 and 1.1. Electrochemical impedance spectra (EIS) also shows that the impedance of the cell with A/C ratio of 1.1 and c-rate of 1C has the smallest impedance. A mathematical model has been established for the relationship between the normalized capacity and number of charge/discharge cycles. Results show that the model calculations agree well with the experimental data.
The post-mortem SEM photos of cathode indicate that SEI becomes more obvious with increasing cycling time. After 200 cycles at 1C, a thin layer of SEI can be found, however, the effect of A/C ratio on the formation of SEI is not obvious. It can be found from SEM photos of anode that lower c-rate (0.2 and 0.5C) gives thicker SEI film. After 1C charge/discharge for 200 cycles, SEI forms in anode and its thickness increases with increasing A/C ratio.
The lattice constant calculation from XRD shows that at the same A/C ratio of 1.1, the cell with c-rate of 0.2C decreases most in a-axis and increases most in c-axis. In addition, at the same c-rate of 1C, the cell with A/C ratio of 0.9 also decreases most in a-axis and increases most in c-axis. It is asserted that the loss of movable lithium ion is the most for this case, which is in consistent with the experimental results of capacity fading.
Advisor Committee Jan-Chen Hong - advisor
Fu-Ming Wang - co-chair
She-huang Wu - co-chair
Files Date of Defense 2016-07-29 Date of Submission 2016-08-15