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URN etd-0912114-110715 Statistics This thesis had been viewed 1831 times. Download 50 times. Author Je-Jang Shiu Author's Email Address No Public. Department Materials Engineering Year 2013 Semester 2 Degree Ph.D. Type of Document Doctoral Dissertation Language English Page Count 218 Title Preparation and characterization of spinel LiNi0.5Mn1.5O4 cathode materials Keyword surface modification spinel cation ion substitution spray pyrolysis method LiNi0.5Mn1.5O4 LiNi0.5Mn1.5O4 spray pyrolysis method cation ion substitution spinel surface modification Abstract Spinel LiNi0.5Mn1.5O4-based cathode materials were prepared via spray pyrolysis method followed by heat treatment at temperatures between 600 and 1000°C, and post annealing at 700°C. The physical and the electrochemical properties of the prepared LiNi0.5Mn1.5O4, partially Mg substituted for Ni, and ZnO/TiO2 coated samples were investigated. The crystalline structure, composition, and morphology were studied by XRD, NPD, ICP-OES, SEM and FEG-TEM, the valence of Mn in the prepared samples was analyzed by XAS, and the electrochemical properties were analyzed by capacity retention, cyclic voltammeteric, and electrochemical impedance spectroscopic studies with LiNi0.5Mn1.5O4/Li coin-type and LiNi0.5Mn1.5O4/Li4Ti5O12 pouch-type cells. Dissolution test was also performed to estimate the amount of cation dissolution and hope to reveal the mechanism of capacity fading.
The results of NPD study indicate that the LiNi0.5Mn1.5O4 prepared at temperatures between 600 and 1000°C crystalize into spinel with space groups of order P4332 and disordered . 700°C prepared and post annealed samples prevail with ordered P4332, whereas samples prepared at other temperatures form into Fd3m primarily. Among the samples prepared at temperatures between 600 and 1000°C, 900°C sample shows the best cycling performance and the highest rate capability. Partially Mg substituted samples manifest enhancement in the formation of ordered P4332 space group and inhibition of the capacity fade. ZnO or TiO2 surface-coating can effectively suppress the cation dissolution and the capacity fading. From the cycling performance of LiNi0.5Mn1.5O4/Li4Ti5O12 cell, it can be found that this kind of cell exhibits excellent capacity retention and rate capability. It manifests initial capacity of 114 and 90 mAh per gram of LNMO and retention rate of 90% and 91% after 50 cycles at 0.1 and 2C rates, respectively.
Advisor Committee She-huang Wu - advisor
Chia-Chin Chang - co-chair
Jeng-Yu Lin - co-chair
Nae-Lih Wu - co-chair
Yi Hu - co-chair
Files Date of Defense 2014-07-30 Date of Submission 2014-09-12