Browsing by Author "Du, GD"

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    Br-doped Li4Ti5O12 and composite TiO2 anodes for Li-ion batteries: synchrotron x-ray and in situ neutron diffraction studies
    (John Wiley & Sons, Inc, 2011-09-01) Du, GD; Sharma, N; Peterson, VK; Kimpton, JA; Jia, DZ; Guo, ZP
    Synchrotron X-ray diffraction data were used to determine the phase purity and re-evaluate the crystal-structure of Li4Ti5O12-xBrx electrode materials (where the synthetic chemical inputs are x = 0.05, 0.10 0.20, 0.30). A maximum of x′ = 0.12 Br, where x′ is the Rietveld-refined value, can be substituted into the crystal structure with at least 2% rutile TiO2 forming as a second phase. Higher Br concentrations induced the formation of a third, presumably Br-rich, phase. These materials function as composite anodes that contain mixtures of TiO2, Li4Ti5O12-xBrx, and a Br-rich third, unknown, phase. The minor quantities of the secondary phases in combination with Li4Ti5O12-xBrx where x′ ∼ 0.1 were found to correspond to the optimum in electrochemical properties, while larger quantities of the secondary phases contributed to the degradation of the performance. In situ neutron diffraction of a composite anatase TiO2/Li4Ti5O12 anode within a custom-built battery was used to determine the electrochemical function of the TiO2 component. The Li4Ti5O12 component was found to be electrochemically active at lower voltages (1.5 V) relative to TiO2 (1.7 V). This enabled Li insertion/extraction to be tuned through the choice of voltage range in both components of this composite or in the anatase TiO2 phase only. The use of composite materials may facilitate the development of multi-component electrodes where different active materials can be cycled in order to tune power output. Copyright © 2011 Wiley-VCH Verlag GmbH & Co.
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    Direct evidence of concurrent solid-solution and two-phase reactions and the nonequilibrium structural eEvolution of LiFePO(4)
    (American Chemical Society, 2012-05-09) Sharma, N; Guo, XW; Du, GD; Guo, ZP; Wang, JZ; Wang, ZX; Peterson, VK
    Lithium-ion batteries power many portable devices and in the future are likely to play a significant role in sustainable-energy systems for transportation and the electrical grid. LiFePO(4) is a candidate cathode material for second-generation lithium-ion batteries, bringing a high rate capability to this technology. LiFePO(4) functions as a cathode where delithiation occurs via either a solid-solution or a two-phase mechanism, the pathway taken being influenced by sample preparation and electrochemical conditions. The details of the delithiation pathway and the relationship between the two-phase and solid-solution reactions remain controversial. Here we report, using real-time in situ neutron powder diffraction, the simultaneous occurrence of solid-solution and two-phase reactions after deep discharge in nonequilibrium conditions. This work is an example of the experimental investigation of nonequilibrium states in a commercially available LiFePO(4) cathode and reveals the concurrent occurrence of and transition between the solid-solution and two-phase reactions. © 2012, American Chemical Society.
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    In situ neutron powder diffraction using custom-made lithium-ion batteries
    (Jove, 2014-011-10) Brant, WR; Schmid, S; Du, GD; Brand, G; Pang, HEA; Peterson, VK; Guo, ZP; Sharma, N
    Li-ion batteries are widely used in portable electronic devices and are considered as promising candidates for higher-energy applications such as electric vehicles.1,2 However, many challenges, such as energy density and battery lifetimes, need to be overcome before this particular battery technology can be widely implemented in such applications.3 This research is challenging, and we outline a method to address these challenges using in situ NPD to probe the crystal structure of electrodes undergoing electrochemical cycling (charge/discharge) in a battery. NPD data help determine the underlying structural mechanism responsible for a range of electrode properties, and this information can direct the development of better electrodes and batteries. We briefly review six types of battery designs custom-made for NPD experiments and detail the method to construct the ‘roll-over’ cell that we have successfully used on the high-intensity NPD instrument, WOMBAT, at the Australian Nuclear Science and Technology Organisation (ANSTO). The design considerations and materials used for cell construction are discussed in conjunction with aspects of the actual in situ NPD experiment and initial directions are presented on how to analyze such complex in situ data.
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    In-situ neutron diffraction study of the MoS2 anode using a custom-built li-ion battery
    (Elsevier, 2011-09-28) Sharma, N; Du, GD; Studer, AJ; Guo, ZP; Peterson, VK
    This work presents the first in-situ neutron diffraction study of the MoS2 electrode, undertaken in a custom-built li-ion battery during discharge. A review of custom-designed cells for in-situ neutron diffraction experiments is presented along with our optimised cell, which we use to show real-time information corresponding to Li-insertion into MoS2 via disappearance of the (103) reflection and increase in the d-spacing of the (002) reflection. The changes in the diffraction patterns begin at the 1.1 V plateau and are complete during the 0.5 V plateau. Sequential Rietveld-refinement indicates the presence of an intermediate lithiated phase (LixMoS2) between MoS2 and LiMoS2. We observe the disappearance of all reflections for the MoS2, corresponding to the loss of long-range order, during the 0.5 V plateau and no new diffraction peaks appear with further electrochemical cycling. This result is indicative of a transformation from long-range ordered MoS2 to short-range ordered LiMoS2, a result that we confirm using ex-situ synchrotron X-ray and neutron diffraction. © 2011, Elsevier Ltd.
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    Non-stoichiometric Mn doping in olivine lithium iron phosphate: structure and electrochemical properties
    (Australian Institute of Physics, 2011-02-02) Feng, C; Li, HH; Du, GD; Guo, ZP; Sharma, N; Peterson, VK; Li, HJ
    LiFePO4 and [Li0.918(10)Fe0.01][Fe0.99Mn0.01]PO4 or 1% Mn-doped LiFePO4 were synthesized by the one-step rheological phase reaction method using inexpensive FePO4 as the main raw material. Synchrotron X-ray diffraction, neutron powder diffraction, and transmission electron microscopy were used to characterize LiFePO4 and Mn-doped LiFePO4. Particle sizes were found to be distributed in the range of 0.5 to 1 μm and the carbon-content in the as-prepared samples was around 2 wt%. Rietveld analysis suggests 1 % Mn-doping replaces 1 % Fe from the Fe (M2) site and places this fraction of Fe on the Li (M1) site. The first process on the M2 site is isovalent doping (Mn2+ for Fe2+), while the second process on M2 is supervalent doping (Fe2+ for Li+). The second process requires that Li vacancies exist for charge balance and our simultaneous refinements against neutron and synchrotron X-ray diffraction data indicate an amount of Li vacancies consistent with this requirement. This doping regime agrees with the observed enhancement of the electrochemical properties of the Mn-doped LiFePO4 compared to the undoped LiFePO4. The Mn-doped LiFePO4 cathodes exhibit higher capacity and better cycling performance than the pure LiFePO4.
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    A simple electrochemical cell for in-situ fundamental structural analysis using synchrotron X-ray powder diffraction
    (Elsevier Science BV, 2013-12-15) Brant, WR; Schmid, S; Du, GD; Gu, QF; Sharma, N
    A simple in-situ cell design is formulated based on the various in-situ electrochemical cells developed over the last three decades. The cell is targeted at those researchers who are not necessarily in the field of lithium ion battery research but are interested in synthesising and performing fundamental structural analyses of compounds that cannot be made via any other route. Therefore, this design uses only components that are routinely available and can be machined in-house. The effectiveness of the initial cell design is demonstrated through kinetic analysis of the lithium insertion reaction for the Li0.18Sr0.66Ti0.5Nb0.5O3 defect perovskite using data obtained from hundreds of diffraction patterns. Within the first discharge it has been possible to identify three regions with different rates of crystal lattice expansion. These regions extend from 1.01 to 1.47 V, 1.47-1.58 V and 1.58-2.07 V with rates of crystal lattice expansion determined to be 1.765(6) x 10(-5) angstrom min(-1), 1.44(5) x 10(-5) angstrom min(-1) and 2.47(1) x 10(-5) angstrom min(-1), respectively. These three regions correlate with three distinct regions in the electrochemical profile, between 1.00 and 1.36 V, 1.36-1.55 V and 1.55-1.80 V. © 2013, Elsevier Ltd.
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    Time-dependent in-situ neutron diffraction investigation of a Li(Co0.16Mn1.84)O4 cathode
    (American Chemical Society, 2011-11-03) Sharma, N; Reddy, MV; Du, GD; Adams, S; Chowdari, BVR; Guo, ZP; Peterson, VK
    Real-time in-situ neutron diffraction data reveal for the first time that the Li(Co0.16Mn1.84)O4 cathode undergoes current-free discharge. We find that current-free discharge occurs in a partially charged Li(Co0.16Mn1.84)O4 cathode during its first charge cycle over a period of 11 h resulting in a 44(2)% expansion of the crystal lattice. The rate of change in the lattice parameter during the current-free discharge process is half the rate and more linear than for an applied-current discharge of ?0.5 mA. The origins of current-free discharge are discussed along with the implications of nonequilibrium relaxation processes in in-situ neutron and X-ray diffraction studies. We show that the lattice does not return to the predischarge values after either current-applied or current-free discharge, indicating a limited ability for Li reinsertion (capacity loss) in partially charged Li(Co0.16Mn1.84)O4 batteries. © 2011, American Chemical Society
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    TiO2(B)@anatase hybrid nanowires with highly reversible electrochemical performance
    (Elsevier, 2011-01-01) Zang, ZX; Du, GD; Guo, ZP; Yu, XB; Chen, ZX; Guo, TL; Sharma, N; Liu, HK
    Novel TiO2(B)@anatase hybrid nanowires with a bicrystalline structure consisting of TiO2(B) core and anatase shell exhibit superior Li ion storage capacities, cycling stability and rate capability. Owing to the excellent electrochemical performance, TiO2(B)@anatase hybrid nanowires could be promising anode materials for lithium ion batteries. Crown Copyright (C) 2010 Published by Elsevier B.V.