Browsing by Author "Shiu, JJ"

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    In-situ neutron diffraction study of the simultaneous structural evolution of a LiNi0.5Mn1.5O4 cathode and a Li4Ti5O12 anode in a LiNi0.5Mn1.5O4 parallel to Li4Ti5O12 full cell
    (Elsevier Science BV, 2014-01-15) Pang, WK; Sharma, N; Peterson, VK; Shiu, JJ; Wu, SH
    In this study, the application of neutron powder diffraction on studying the time-resolved structural evolution of a cell comprised with LiNi0.5Mn1.5O4 cathode and Li4Ti5O12 anode during charge–discharge cycling is demonstrated. As expected, the lattices of the LiNi0.5Mn1.5O4 cathode and the Li4Ti5O12 anode in the cell are found to simultaneously contract during charging and expand during discharging. It is found that for the LiNi0.5Mn1.5O4 cathode a solid-solution reaction is associated with the lattice change and the Ni2+/Ni3+ redox couple between 3.06 and 3.16 V (vs. Li4Ti5O12), and a two-phase reaction between LixNi0.5Mn1.5O4 and Ni0.25Mn0.75O2 is corresponding to the Ni3+/Ni4+ redox couple at voltage higher than 3.22 V (vs. Li4Ti5O12) without a corresponding change in lattice. The oxidation states of the metals in the electrodes are determined by tracking the associated change in the oxygen position. In addition, the Ti oxidation state is correlated to the intensity of the Li4Ti5O12 222 reflection at the anode, and the determined oxidation state of the Ni is correlated to the lithium occupancy within the cathode. Furthermore, the small volume changes of the cathode and the anode upon cycling suggest that the cell chemistry is favorable for practical applications. © 2014, Elsevier Ltd.
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    Lithium migration in Li4Ti5O12 studied using in situ neutron powder diffraction
    (ACS Publications, 2014-03-14) Pang, WK; Peterson, VK; Sharma, N; Shiu, JJ; Wu, SH
    We used in situ neutron powder diffraction (NPD) to study the migration of Li in Li4Ti5O12 anodes with different particle sizes during battery cycling. The motivation of this work was to uncover the mechanism of the increased capacity of the battery made with a smaller-particle-sized anode. In real time, we monitored the anode lattice parameter, Li distribution, and oxidation state of the Ti atom, and these suggested an increase in the rate of Li incorporation into the anode rather than a change in the migration pathway as a result of the particle size reduction. The lattice of these anodes during continuous lithiation undergoes expansion followed by a gradual contraction and then expansion again. The measured lattice parameter changes were reconciled with Li occupation at specific sites within the Li4Ti5O12 crystal structure, where Li migrates from the 8a to 16c sites. Despite these similar Li-diffusion pathways, in larger-particle-sized Li4Ti5O12 the population of Li at the 16c site is accompanied by Li depopulation from the 8a site, which is in contrast to the smaller-particle-sized anode where our results suggest that Li at the 8a site is replenished faster than the rate of transfer of Li to the 16c site. Fourier-difference nuclear density maps of both anodes suggest that 32e sites are involved in the diffusion pathway of Li. NPD is again shown to be an excellent tool for the study of electrode materials for Li-ion batteries, particularly when it is used to probe real-time crystallographic changes of the materials in an operating battery during charge–discharge cycling. © 2014, American Chemical Society.
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    Structural evolution of a LiNi0.5Mn1.5O4 cathode and a Li4Ti5O12 anode in a functioning lithium-ion battery
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2013-12-03) Pang, WK; Peterson, VK; Sharma, N; Shiu, JJ; Wu, SH
    The relatively large penetration depth, sensitivity to light elements, and non-destructive sample interaction afforded by neutron scattering is combined with instrumentation allowing fast data-acquisition times to allow neutron powder diffraction (NPO) to be a powerful tool for studying the structural variation of cathode and anode materials during battery cycling. In this study, a neutron-friendly battery comprised of a disordered LiNi0.5Mn1.5O4 (Fd3m) cathode, a Li4Ti5O12 anode, deuterated electrolyte, and the relatively low-hydrogen polyvinylidene difluoride separator was used to research a battery chemistry not yet commercially available. This work tracks crystallographic changes such as the variation of lattice parameters, lithium occupation, and oxygen positional parameters of the LiNi0.5Mn1.5O4 cathode and Li4Ti5O12} anode simultaneously with charge/discharge within a battery. Importantly, we find that the disordered LiNi0.5Mn1.5O4 cathode has a solid-solution reaction associated with its lattice change and the Ni2+/Ni3+ redox couple, and a two-phase reaction, between Li xNi0.5Mn1.5O4 and Ni0.25Mn0.75O2, that is related to the Ni3+/Ni4+ redox couple without a corresponding change in lattice. The details of these findings will be presented.
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    Structure of the Li4Ti5O12 anode during charge-discharge cycling
    (Cambridge University Press, 2014-11-10) Pang, WK; Peterson, VK; Sharma, N; Shiu, JJ; Wu, SH
    The structural evolution of the “zero-strain” Li4Ti5O12 anode within a functioning Li-ion battery during charge–discharge cycling was studied using in situ neutron powder-diffraction, allowing correlation of the anode structure to the measured charge–discharge profile. While the overall lattice response controls the “zero-strain” property, the oxygen atom is the only variable in the atomic structure and responds to the oxidation state of the titanium, resulting in distortion of the TiO6 octahedron and contributing to the anode's stability upon lithiation/delithiation. Interestingly, the trend of the octahedral distortion on charge–discharge does not reflect that of the lattice parameter, with the latter thought to be influenced by the interplay of lithium location and quantity. Here we report the details of the TiO6 octahedral distortion in terms of the O–Ti–O bond angle that ranges from 83.7(3)° to 85.4(5)°. © 2014, International Centre for Diffraction Data.