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Gerbrand Ceder. Ma, Xiaohua, Ph. D. Massachusetts Institute of Technology Massachusetts Institute of Technology. Department of Materials Science and Engineering. Massachusetts Institute of Technology. Department of Materials Science and Engineering 2016-03-25T13:41:14Z 2016-03-25T13:41:14Z 2012 2012 http://hdl.handle.net/1721.1/101862 944028297 Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2012. Cataloged from PDF version of thesis. Includes bibliographical references. A new layered compound LiNi2/3Sb1/30 2 was synthesized and tested electrochemically to understand the effect of the transition metals on the structural stability of the layered compound upon Li de-intercalation. The electrochemical results show that the structure of LiNi2/3Sb1 /302 degrades upon cycling. XRD pattern refinement and TEM diffraction on the cycled LiNi2/3 Sb1/3O2 indicate that the structure degradation is associated with the migration of Ni into the Li layer. First principles calculation also shows a very low barrier for the migration of a divalent Ni from the transition metal layer to the tetrahedral sites of the lithium layer in the partially delithiated Li2/3Ni2/3Sbl/3O2. The divalent Ni becomes highly mobile because of the strong electrostatic repulsion from the surrounding three Ni3+ and three Sb5+. The effect of the alkali ions on the structural stability in the layered AMO 2 (A = alkali ion; M = transition metals) compounds is discussed by comparing layered LiMnO2 and NaMnO2. The structure of layered LiMnO 2 transforms rapidly into a spinel-like structure upon delithation due to the formation of a Li/Mn dumbbell configuration. However, such kind of dumbbell does not form in NaxMnO2, indicating its better structural stability upon deintercalation. The electrochemical results of NaMnO 2 show a much better capacity retention than that of LiMnO2, confirming that NaMnO2 is more stable than LiMnO2 upon deintercalation. The XRD results of the cycled NaMnO2 also show no significant structural change. The pronounced voltage steps and plateaus of NaMnO2 upon cycling were also investigated. First principles calculations show that the Li diffusivity in LiNi0.5Mn5O4 is in the order of 10-9 cm 2/s, implying that LiNi0.5Mn1.5O4 can be a high rate material even with a large particle size. The electrochemical tests of the micron-sized LiNiO0.5Mn1.5O4 show higher rate capability than nano LiNi0.5Mn1.5O4 by Shaju, et al, indicating that the ionic and electronic transport may not be the rate limiting factors. It was also found that cell configurations, such as separators, mechanical pressure of the cell and the carbon content in the electrode, could dramatically affect the rate capability of the cell. When the cell is highly optimized in configuration, more than half of the theoretical capacity is obtained at a discharge rate of 167C (corresponding to 22 seconds) with a particle size in the range of 3-5 [mu]m, which agrees with the high Li diffusivity by my calculation. by Xiaohua Ma. Ph.D. 130 pages eng Massachusetts Institute of Technology M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 Materials Science and Engineering. Understanding and designing high power and high energy density cathode materials for lithium ion batteries by experiments and first principles computations Thesis application/pdf false Publication unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="2275c65b-1b7c-4c7b-8f3b-a5eccf77ac48"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Language>eng</Language> <Title>Understanding and designing high power and high energy density cathode materials for lithium ion batteries by experiments and first principles computations</Title> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>2012</PublicationDate> <Authors> <Author> <DisplayName>Ma, Xiaohua, Ph. D. Massachusetts Institute of Technology</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>http://dspace.mit.edu/handle/1721.1/7582</License> <Keyword>Materials Science and Engineering.</Keyword> <Abstract>A new layered compound LiNi2/3Sb1/30 2 was synthesized and tested electrochemically to understand the effect of the transition metals on the structural stability of the layered compound upon Li de-intercalation. The electrochemical results show that the structure of LiNi2/3Sb1 /302 degrades upon cycling. XRD pattern refinement and TEM diffraction on the cycled LiNi2/3 Sb1/3O2 indicate that the structure degradation is associated with the migration of Ni into the Li layer. First principles calculation also shows a very low barrier for the migration of a divalent Ni from the transition metal layer to the tetrahedral sites of the lithium layer in the partially delithiated Li2/3Ni2/3Sbl/3O2. The divalent Ni becomes highly mobile because of the strong electrostatic repulsion from the surrounding three Ni3+ and three Sb5+. The effect of the alkali ions on the structural stability in the layered AMO 2 (A = alkali ion; M = transition metals) compounds is discussed by comparing layered LiMnO2 and NaMnO2. The structure of layered LiMnO 2 transforms rapidly into a spinel-like structure upon delithation due to the formation of a Li/Mn dumbbell configuration. However, such kind of dumbbell does not form in NaxMnO2, indicating its better structural stability upon deintercalation. The electrochemical results of NaMnO 2 show a much better capacity retention than that of LiMnO2, confirming that NaMnO2 is more stable than LiMnO2 upon deintercalation. The XRD results of the cycled NaMnO2 also show no significant structural change. The pronounced voltage steps and plateaus of NaMnO2 upon cycling were also investigated. First principles calculations show that the Li diffusivity in LiNi0.5Mn5O4 is in the order of 10-9 cm 2/s, implying that LiNi0.5Mn1.5O4 can be a high rate material even with a large particle size. The electrochemical tests of the micron-sized LiNiO0.5Mn1.5O4 show higher rate capability than nano LiNi0.5Mn1.5O4 by Shaju, et al, indicating that the ionic and electronic transport may not be the rate limiting factors. It was also found that cell configurations, such as separators, mechanical pressure of the cell and the carbon content in the electrode, could dramatically affect the rate capability of the cell. When the cell is highly optimized in configuration, more than half of the theoretical capacity is obtained at a discharge rate of 167C (corresponding to 22 seconds) with a particle size in the range of 3-5 [mu]m, which agrees with the high Li diffusivity by my calculation.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>