Browsing by Author "Lee, CH"

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    Capacity enhancement of the quenched Li-Ni-Mn-Co oxide high-voltage Li-ion battery positive electrode
    (Elsevier, 2017-03-23) Jena, A; Lee, CH; Pang, WK; Peterson, VK; Sharma, N; Wang, CC; Song, YF; Lin, CC; Chang, H; Liu, RS
    Li-rich metal oxides, regarded as a high-voltage composite cathode, is currently one of the hottest positive electrode material for lithium-ion batteries, due to its high-capacity and high-energy performance. The crystallography, phase composition and morphology can be altered by synthesis parameters, which can influence drastically the capacity and cycling performance. In this work, we demonstrate Li1.207Ni0.127Mn0.54Co0.127O2, obtained by a co-precipitation method, exhibits super-high specific capacity up to 298 mAh g−1 and excellent capacity retention of ∼100% up to 50 cycles. Using neutron powder diffraction and transmission X-ray microscopy, we have found that the cooling-treatments applied after sintering during synthesis are crucially important in controlling the phase composition and morphology of the cathodes, thereby influencing the electrochemical performance. Unique spherical microstructure, larger lattice, and higher content of Li-rich monoclinic component can be achieved in the rapid quenching process, whereas severe particle cracking along with the smaller lattice and lower monoclinic component content is obtained when natural cooling of the furnace is applied. Combined with electrochemical impedance spectra, a plausible mechanism is described for the poorer specific capacity and cycling stability of the composite cathodes. © 2017 Elsevier Ltd.
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    Complex magnetic incommensurability in multiferroic Co3TeO6
    (International Conference on Neutron Scattering, 2017-07-12) Lee, CH; Wang, CW; Zhao, Y; Li, WH; Lynn, JW; Harris, AB; Rule, KC; Yang, HD; Berger, H
    Monoclinic cobalt tellurate Co3TeO6 has been characterized1-3 as a type-II multiferroic, where the order parameters of electrical polarization and spontaneous magnetization are closely coupled.4,5 In this study, polarized and unpolarized neutron diffractions have been carried out to investigate the nature of the magnetic structures and transitions in monoclinic Co3TeO6. As the temperature is lowered below TM1= 26 K long range order develops, which is fully incommensurate (ICM) in all three crystallographic directions in the crystal. Below TM2 = 19.5 K, additional commensurate magnetic peaks develop, consistent with the ?4 irreducible representation, along with a splitting of the ICM peaks along the h direction which indicates that there are two separate sets of magnetic modulation vectors. Below TM3 = 18 K, this small additional magnetic incommensurability disappears, ferroelectricity develops, a commensurate ?3 irreducible representation appears, and the k component of the ICM wave vector disappears. Below TM4= 15 K the k component of the ICM structure reappears, along with second-order ICM Bragg peaks, which polarized neutron data demonstrate are magnetic in origin.
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    Fe-excess ions as electronic charge suppliers for zero thermal expansion in the normal state of Fe1.16Te0.6Se0.4
    (The Physical Society of Japan, 2015-08-27) Karna, SK; Lee, CH; Li, WH; Sankar, R; Chou, FC; Avdeev, M
    We report on the observation of a zero thermal expansion of the crystalline lattice of Fe1.16Te0.6Se0.4 in the normal state, using neutron and x-ray diffraction, ac magnetic susceptibility, magnetization and resistivity measurements. Superconductivity develops below 15 K. Magnetic hysteresis loops are revealed at all temperatures studied, with the loop opening at 5 K being noticeably larger than that at 300 K. An extremely large thermal expansion of the lattice is observed in the superconducting state. Thermal expansion coefficients of the lattice are quenched upon loss of superconductivity. Zero thermal expansion is retained over a very broad temperature range from 20 to 200 K. These behaviors are understood as being due to the electronic charge redistribution, in which the excess Fe ions on the interstitial sites act as electronic charge suppliers that strengthen the electronic connections between the Te/Se and Fe ions on the lattice sites once the temperature is raised. ©2015 The Physical Society of Japan
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    Magnetic properties and noncollinear spin structure of the tin-rich stannide Ho5Co6Sn18
    (American Physical Society, 2022-03-28) Wang, CW; Karna, SK; Yanco, SI; Lee, CH; Avdeev, M; Lue, CS; Kuo, CN
    We have investigated the magnetic, structural, and thermodynamic properties of Ho5Co6Sn18 through x-ray and neutron diffraction, magnetization, and specific heat measurements. Ho5Co6Sn18 displays a magnetic transition at TM=3.4K and can be described with the magnetic space group I41/ac′d′. The two holmium sublattices Ho(1) and Ho(2) exhibit different magnetic behaviors. Ferromagnetic order on the Ho(1) site develops into a net magnetization along the c axis below TM. In contrast, the ordering of the Ho(2) site is determined by geometric magnetic frustrations. The Ho(2) spins order into the noncollinear, two-in-two-out antiferromagnetic pattern on the Ho(2)4 tetrahedron. At 60 mK, the ordered moment of Ho(2) reaches 4.01(8)μB, which is about half of the Ho(1) moment. Upon the application of a magnetic field, ferromagnetic components along the c axis are induced on Ho(2), along with the in-plane antiferromagnetic components, indicating the XY-like spin anisotropy of the Ho(2) spins. A magnetic quasielastic neutron scattering signal is observed above TM and significantly weakens with the magnetic ordering. ©2022 American Physical Society.
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    On the nature of the spin frustration in the CuO(2) ribbon chains of LiCuVO(4): crystal structure determination at 1.6 K, magnetic susceptibility analysis, and density functional evaluation of the spin exchange constants
    (American Chemical Society, 2011-04-18) Koo, HJ; Lee, CH; Whangbo, MH; McIntyre, GJ; Kremer, RK
    The spin-1/2 Cu(2+) ions of LiCuVO(4) form one-dimensional chains along the b direction, and the spin frustration in LiCuVO(4) is described in terms of the nearest-neighbor ferromagnetic exchange h and the next-nearest-neighbor antiferromagnetic exchange J(2) in these chains. Recently, it has become controversial whether or not J(1) is stronger in magnitude than J(2). To resolve this controversy, we determined the crystal structure of LiCuVO(4) at 1.6 K by neutron diffraction, analyzed the magnetic susceptibility of LiCuVO(4) to deduce the Curie-Weiss temperature theta and the J(2)/J(1) ratio, and finally extracted the spin exchange constants of LiCuVO(4) on the basis of density functional calculations. Our work shows unambiguously that the Curie-Weiss temperature theta of LiCuVO(4) is negative in the range of -20 K, so that J(2) is substantially stronger in magnitude than J(1). © 2011, American Chemical Society
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    Real-time investigation of the structural evolution of electrodes in a commercial lithium-ion battery containing a V-added LiFePO4 cathode using in-situ neutron powder diffraction
    (Elsevier Science BV, 2013-12-15) Hu, CW; Sharma, N; Chiang, CY; Su, HC; Peterson, VK; Hsieh, HW; Lin, YF; Chou, WC; Shew, BY; Lee, CH
    In-situ neutron powder diffraction was employed to investigate the structural evolution of the electrode materials in a commercial lithium-ion battery used for electric buses in Taiwan. The battery, containing a vanadium-added LiFePO4 cathode, does not exhibit a delayed phase transition between LiFePO4 (triphylite) and FePO4 (heterosite) suggesting that the delayed phase transition can be suppressed through the use of vanadium-added LiFePO4 cathodes, which also enhances the capacity and prolongs the cycle life of these batteries. Furthermore, we characterize the readily reversible structural change of the anode (LixC6 where 0 < x <= 1) and correlate this to battery voltage. © 2013, Elsevier Ltd.
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    Vanadium substitution of LiFePO4 cathode materials to enhance the capacity of LiFePO4-based lithium-Ion batteries
    (American Chemical Society, 2012-11-22) Chiang, CY; Su, HC; Wu, PJ; Liu, HJ; Hu, CW; Sharma, N; Peterson, VK; Hsieh, HW; Lin, YF; Chou, WC; Lee, CH; Lee, JF; Shew, BY
    The mechanism of enhancing the capacity of the LiFePO(4) cathodes in lithium ion batteries by the addition of a small amount of vanadium, which locate on the lithium site and induce lithium vacancies in the crystal structure, is reported in this article. As a result, the capacity increases from 138 mAh/g found for pristine LiFePO(4) to 155 mAh/g for the V-added compound, and the conductivity increases from 4.75 x 10(-4) S/cm for the LiFePO(4) without V addition to 1.9 x 10(-2) S/cm for the V-added compound. A possible model to facilitate the enhancement of conductivity and capacity is described with evidence supported by X-ray powder diffraction, X-ray absorption spectroscopy, and neutron powder diffraction data. © 2012, American Chemical Society.