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Yangkook Sun - One of the best experts on this subject based on the ideXlab platform.
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lini0 5mn1 5 o 4 showing reversible phase transition on 3 v region
Electrochemical and Solid State Letters, 2005Co-Authors: Sang Ho Park, Chongseung Yoon, Seungtaek Myung, Yangkook SunAbstract:Spinel LiNi 0 . 5 Mn 1 . 5 O 4 powders with different space group of Fd3m and P4 3 32 were synthesized by an ultrasonic spray pyrolysis method. The morphologies of the prepared powders depended on their structures; polyhedral shape for Fd3m and octahedral for P4 3 32. The obtained discharge capacities of the Fd3m and P4 3 32 were about 60 mAh g - 1 and 70 mAh g - 1 , respectively. Structural changes of both compounds were investigated on 3 V region by ex situ X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). From the ex situ XRD and HRTEM studies, LiNi 0 . 5 Mn 1 . 5 O 4 having P4 3 32 symmetry showed that structural transition occurred reversibly from simple cubic (P4 3 32) to tetragonal phase (I4 1 /amd), whereas irreversible structural changes were observed for Fd3m symmetry on 3V region.
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phase transitions in li1 δ ni0 5mn1 5 o 4 during cycling at 5 v
Electrochemical and Solid State Letters, 2004Co-Authors: Junghyun Kim, Chongseung Yoon, Seungtaek Myung, Jai Prakash, Yangkook SunAbstract:Structural change of LiNi 0 . 5 Mn 1 . 5 O 4 with two different crystallographic structures of Fd3m and P4 3 32 was studied during Li extraction. Ex situ X-ray diffraction and transmission electron microscopy studies on partially delithiated Li 1 - δ Ni 0 . 5 Mn 1 . 5 O 4 revealed that LiNi 0 . 5 Mn 1 . 5 O 4 (Fd3m) structure lost its characteristic diagonal glide symmetry, suggesting a structural transition arising from the possible migration of cations during oxidation from Ni 2 + to Ni 4 + . For the Li 1 - δ Ni 0 . 5 Mn 1 . 5 O 4 (P4 3 32), ordering of cations was destroyed by random migration of cations during Li extraction, resulting in the formation of intermediate phase with the Fd3m structure. The phase transitions were reversible, meaning that migration of cations is highly reversible during lithiation/delithiation.
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comparative study of lini0 5mn1 5o4 δ and lini0 5mn1 5o4 cathodes having two crystallographic structures fd3m and p4332
Chemistry of Materials, 2004Co-Authors: Junghyun Kim, Chongseung Yoon, Seungtaek Myung, Sung Goon Kang, Yangkook SunAbstract:Nonstoichiometric LiNi0.5Mn1.5O4-δ and stoichiometric LiNi0.5Mn1.5O4 cathodes with two different structures (Fd3m and P4332) were synthesized by a molten salt method. Rietveld refinement of the X-ray diffraction (XRD) data and a selected-area electron diffraction (SAED) study confirmed that the face-centered spinel (Fd3m) transformed to the primitive simple cubic (P4332) upon additional heating at 700 °C. The LiNi0.5Mn1.5O4-δ cathode having the space group of Fd3m showed better electrochemical behaviors than did the LiNi0.5Mn1.5O4 cathode with the space group of P4332, specifically, a lower area-specific impedance (ASI) and a higher discharge capacity during cycling at high rate. XRD and SAED showed that both stoichiometric and nonstoichiometric LiNi0.5Mn1.5O4-δ exhibited similar SAED patterns with extra 002 spots at the fully delithiated state, suggesting a structural transition arising from the possible migration of transition metal cations during Li extraction. In addition, stoichiometric LiNi0.5Mn1...
Eric A Stach - One of the best experts on this subject based on the ideXlab platform.
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investigation of changes in the surface structure of lixni0 8co0 15al0 05o2 cathode materials induced by the initial charge
Chemistry of Materials, 2014Co-Authors: Sooyeon Hwang, Wonyoung Chang, Seung Min Kim, Donghyun Kim, Jeong Yong Lee, Kyung Yoon Chung, Eric A StachAbstract:We use transmission electron microscopy (TEM) to investigate the evolution of the surface structure of LixNi0.8Co0.15Al0.05O2 cathode materials (NCA) as a function of the extent of first charge at room temperature using a combination of high-resolution electron microscopy (HREM) imaging, selected area electron diffraction (SAED), and electron energy loss spectroscopy (EELS). It was found that the surface changes from the layered structure (space group R3m) to the disordered spinel structure (Fd3m), and eventually to the rock-salt structure (Fm3m), and that these changes are more substantial as the extent of charge increases. EELS indicates that these crystal structure changes are also accompanied by significant changes in the electronic structure, which are consistent with delithiation leading to both a reduction of the Ni and an increase in the effective electron density of oxygen. This leads to a charge imbalance, which results in the formation of oxygen vacancies and the development of surface poros...
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correlating structural changes and gas evolution during the thermal decomposition of charged lixni0 8co0 15al0 05o2 cathode materials
Chemistry of Materials, 2013Co-Authors: Seongmin Bak, Sooyeon Hwang, Wonyoung Chang, Kyung Yoon Chung, Eric A Stach, Kyungwan Nam, Kwangbum Kim, Xiaoqing YangAbstract:In this work, we present results from the application of a new in situ technique that combines time-resolved synchrotron X-ray diffraction and mass spectroscopy. We exploit this approach to provide direct correlation between structural changes and the evolution of gas that occurs during the thermal decomposition of (over)charged cathode materials used in lithium-ion batteries. Results from charged LixNi0.8Co0.15Al0.05O2 cathode materials indicate that the evolution of both O2 and CO2 gases are strongly related to phase transitions that occur during thermal decomposition, specifically from the layered structure (space group R3m) to the disordered spinel structure (Fd3m), and finally to the rock-salt structure (Fm3m). The state of charge also significantly affects both the structural changes and the evolution of oxygen as the temperature increases: the more extensive the charge, the lower the temperature of the phase transitions and the larger the oxygen release. Ex situ X-ray absorption spectroscopy (XA...
Sooyeon Hwang - One of the best experts on this subject based on the ideXlab platform.
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investigation of changes in the surface structure of lixni0 8co0 15al0 05o2 cathode materials induced by the initial charge
Chemistry of Materials, 2014Co-Authors: Sooyeon Hwang, Wonyoung Chang, Seung Min Kim, Donghyun Kim, Jeong Yong Lee, Kyung Yoon Chung, Eric A StachAbstract:We use transmission electron microscopy (TEM) to investigate the evolution of the surface structure of LixNi0.8Co0.15Al0.05O2 cathode materials (NCA) as a function of the extent of first charge at room temperature using a combination of high-resolution electron microscopy (HREM) imaging, selected area electron diffraction (SAED), and electron energy loss spectroscopy (EELS). It was found that the surface changes from the layered structure (space group R3m) to the disordered spinel structure (Fd3m), and eventually to the rock-salt structure (Fm3m), and that these changes are more substantial as the extent of charge increases. EELS indicates that these crystal structure changes are also accompanied by significant changes in the electronic structure, which are consistent with delithiation leading to both a reduction of the Ni and an increase in the effective electron density of oxygen. This leads to a charge imbalance, which results in the formation of oxygen vacancies and the development of surface poros...
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correlating structural changes and gas evolution during the thermal decomposition of charged lixni0 8co0 15al0 05o2 cathode materials
Chemistry of Materials, 2013Co-Authors: Seongmin Bak, Sooyeon Hwang, Wonyoung Chang, Kyung Yoon Chung, Eric A Stach, Kyungwan Nam, Kwangbum Kim, Xiaoqing YangAbstract:In this work, we present results from the application of a new in situ technique that combines time-resolved synchrotron X-ray diffraction and mass spectroscopy. We exploit this approach to provide direct correlation between structural changes and the evolution of gas that occurs during the thermal decomposition of (over)charged cathode materials used in lithium-ion batteries. Results from charged LixNi0.8Co0.15Al0.05O2 cathode materials indicate that the evolution of both O2 and CO2 gases are strongly related to phase transitions that occur during thermal decomposition, specifically from the layered structure (space group R3m) to the disordered spinel structure (Fd3m), and finally to the rock-salt structure (Fm3m). The state of charge also significantly affects both the structural changes and the evolution of oxygen as the temperature increases: the more extensive the charge, the lower the temperature of the phase transitions and the larger the oxygen release. Ex situ X-ray absorption spectroscopy (XA...
Reiner Anwander - One of the best experts on this subject based on the ideXlab platform.
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Facile Mesophase Control of Periodic Mesoporous Organosilicas under Basic Conditions
Chemistry of Materials, 2008Co-Authors: Yucang Liang, Egil Sev. Erichsen, Marianne Hanzlik, Reiner AnwanderAbstract:The mesophase structure of ordered periodic mesoporous organosilicas (PMOs) can be easily adjusted under basic conditions by variation of the sodium hydroxide concentration. PMOs with hexagonal (p6mm, two-dimensional pore system), cubic (Pm3n or Fm3m, three-dimensional cagelike pore system), and disordered hexagonal (MSU-type) symmetry were obtained from 1,2-bis(triethoxysilyl)ethane (BTEE)-derived synthesis gels in the presence of binary surfactant mixtures, [CH3(CH2)15NMe3]+Br− (C16TABr) and [CH3(CH2)nNMe2(CH2)3NMe3]2+2Br− (n = 15, 17), as structure-directing agents. With an increasing amount of NaOH, mesophase−mesophase transitions from p6mm → Pm3n → Fm3m → distorted cubic → MSU-type (3D-network of “wormholelike” mesopores) were evidenced by powder X-ray diffraction analysis and transmission electron microscopy. Slight variations of the NaOH concentration not only affected the PMO mesophase structure via the charge matching principle but also the PMO morphology. Among others, hexagons with smooth faces...
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ethylene bridged periodic mesoporous organosilicas with Fm3m symmetry
Journal of Materials Chemistry, 2005Co-Authors: Yucang Liang, Marianne Hanzlik, Reiner AnwanderAbstract:Divalent surfactant [CH3(CH2)15N(CH3)2(CH2)3N(CH3)3]2+2Br− (C16-3-1) was exploited as a structure directing agent (SDA) for the synthesis of highly ordered periodic mesoporous organosilicas (PMOs) from 1,2-bis(triethoxysilyl)ethane (BTEE) as organosilica source under basic conditions. The mesophase structure/symmetry and the physical parameters could be controlled/optimized by adjusting synthetic parameters such as surfactant and base concentration, hydrothermal aging temperature and time, and crucially the type (charge, shape, aliphatic tail chain length) of the surfactant. Cubic PMO[KIT-5]-n reveals a face-centred Fm3m symmetry similar to that of the previously reported purely siliceous material KIT-5. Under the applied reaction conditions, lower aging temperatures generally afforded PMO[KIT-5] materials with increased BET surface area (max. 840 m2 g−1) and pore volume (max. 0.93 cm3 g−1), however, similar pore size (ca. 3.0 nm). Lower divalent surfactant concentrations (C16-3-1) caused a mesophase transformation from cubic Fm3m to hexagonal P6mm symmetry. Upon relative increase of the base (NaOH) concentration, the PMO mesostructure transformed from hexagonal to cubic, then from cubic to hexagonal symmetry. Surfactants [CH3(CH2)17N(CH3)2(CH2)3N(CH3)3]2+2Br− (C18-3-1), [CH3(CH2)15N(CH3)2(CH2)3-N(C2H5)3]2+2Br− (C16-3-2), and [CH3(CH2)15N(CH3)3]+Br− (C16) were found to encode for PMO[SBA-1]-n and PMO[MCM-41]-n with cubic Pm3n (former) and hexagonal P6mm symmetry (latter two), respectively. All these periodic mesoporous organosilicas were characterized by powder X-ray diffraction (PXRD), nitrogen physisorption, FTIR spectroscopy, 13C and 29Si solid state NMR spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM).
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pmo kit 5 n synthesis of highly ordered three dimensional periodic mesoporous organosilicas with Fm3m symmetry
Chemical Communications, 2005Co-Authors: Yucang Liang, Marianne Hanzlik, Reiner AnwanderAbstract:Divalent surfactant [CH3(CH2)15N(CH3)2(CH2)3N(CH3)3]2+2Br− (C16-3-1) was used as a structure directing agent (SDA) for the synthesis of highly ordered periodic mesoporous organosilicas (PMOs) with cubic Fm3m symmetry from 1,2-bis(triethoxylsilyl)ethane (BTEE) under basic conditions.
Masahiro Yoshimura - One of the best experts on this subject based on the ideXlab platform.
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oxygen induced structural change of the tetragonal phase around the tetragonal cubic phase boundary in zro2 yo1 5 solid solutions
Acta Crystallographica Section B-structural Science, 1994Co-Authors: Masatomo Yashima, S Sasaki, Masato Kakihana, Y Yamaguchi, Haruo Arashi, Masahiro YoshimuraAbstract:In the ZrO 2 -YO 1.5 solid solutions, the phase changes among the cubic phase (Fm3m, Z=4), the t″ form and the t' form were investigated by neutron and X-ray powder diffraction, where the t″ and t' forms are defined as tetragonal phases (P4 2 /nmc, Z=2) with axial ratios of c/a f =1 and c/a f >1, respectively, which were prepared by a diffusionless transition from the high-temperature cubic phase during quenching. a f is the lattice parameter of the pseudo-fluorite cell
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raman scattering study of cubic tetragonal phase transition in zr1 xcexo2 solid solution
Journal of the American Ceramic Society, 1994Co-Authors: Masahiro Yoshimura, Masatomo Yashima, Masato Kakihana, Haruo ArashiAbstract:A structural phase transition between the cubic (space group, Fm3m) and tetragonal (space group, P42/nmc) phases in a zirconia–ceria solid solution (Zr1−xCexO2) has been observed by Raman spectroscopy. The cubic–tetragonal (c–t″) phase boundary in compositionally homogeneous samples exists at a composition X0 (0.8 < X0 < 0.9) at room temperature, where t″ is defined as a tetragonal phase whose axial ratio c/a equals unity. The axial ratio c/a decreases with an increase of ceria concentration and becomes 1 at a composition X′0 (0.65 < X′0 < 0.7) at room temperature. The sample with a composition between X0 and X′0 is t″ ZrO2. By Raman scattering measurements at high temperatures, the tetragonal (t″) → cubic and cubic → tetragonal phase transitions occur above 400°C in Zr0.2 Ce0.8O2 solid solution.