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URN etd-0911117-144059 Statistics This thesis had been viewed 271 times. Download 0 times. Author Cheng-Wei Hung Author's Email Address No Public. Department Materials Engineering Year 2016 Semester 2 Degree Master Type of Document Master's Thesis Language zh-TW.Big5 Chinese Page Count 108 Title The Effects and Characteristics of Lithium-excess and Chlorine-doping for LiNi0.5Mn1.5O4 High-Voltage Cathode Materials Keyword lithium-excess spray-drying method anion substitution LiNi0.5Mn1.5O4 LiNi0.5Mn1.5O4 anion substitution spray-drying method lithium-excess Abstract The chlorine-doping and lithium-excess of LiNi0.5Mn1.5O4 (LNMO) - based cathode materials were prepared by spray-drying method, and their effects on the surface morphology, crystal structure, and electrochemical properties were investigated. From the SEM and PSA data, it was found that the surface morphology and particle size of the synthesized powders were not affected by the doping of chlorine and the excess of lithium ions. It was observed by XRD patterns that the chlorine ion doped in LNMO increase the lattice parameter of the material and can effectively inhibit the formation of rock-salt phase. Similarly, the excess of lithium doped into LNMO will also expand the lattice of the material; however, it also increased the formation of rock-salt phase, which hinders the diffusion of lithium ions. From the FT-IR spectroscopy, it can be seen that both of chlorine-doped and lithium-excess LNMO has mainly disordered phase with the space group of Fd3 ̅m at the 900oC sintering temperature. However, by comparing the ratio of the 586/624 bands, it can be found that the degree of ordering increase with the amount of chlorine doping. On the contrary, the excess of lithium would reduce the ordering of the transition metals in the crystal.
Moreover, it was found that the appropriate amount of chlorine doped in LNMO can improve the capacity and rate capability. It was also proved by dissolution test that chlorine doping can inhibit the dissolution of transition metal ions, which can reduce the chance of electrolyte oxidative decomposition and also improve the coulombic efficiency and retain better cycle life at high temperature. However, the excess of lithium doping in LNMO result in worse electrochemical performance, which was due to the formation of more inactive secondary phase and blocked the diffusion path of lithium ions.
Advisor Committee She-huang Wu - advisor
Jeng-kuei Chang - co-chair
Yi Hu - co-chair
Files Date of Defense 2017-07-31 Date of Submission 2017-09-11