| 11. |
- Brant, William
(author)
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Controlling Cation Ordering and Oxygen Release in LiNi0.5Mn1.5O4
- 2018
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Conference paper (other academic/artistic)abstract
- LiNi0.5Mn1.5O4 (LNMO) is a promising spinel-type positive electrode (cathode) material for lithium-ion batteries (LiBs), with a theoretical capacity of 147 mAh/g and an operating voltage around 4.7 V (vs. Li/Li+). With both high ionic and electronic conductivity it is regarded as a suitable cathode material for high power applications. LMNO can adopt two different structural arrangements, P4332 (cation ordered) or Fd-3m (disordered) [1]. Generally speaking, it has been observed that batteries incorporating the latter structure exhibit reduced capacity fading during electrochemical cycling. However, synthesis conditions leading to disordering also lead to oxygen deficiency, rock-salt impurities and as a result generate Mn3+ [2,3]. Furthermore, while many literature reports categorise the material as either “ordered” or “disordered”, the material can adopt varying degrees of ordering. Thus, isolating the exact cause of capacity fade is challenging. In this study, in-situ neutron diffraction is performed on disordered and slightly Mn-rich LNMO samples (Mn:Ni ratio of 1.56:0.44) to follow cation ordering-disordering transformations during heating and cooling (see figure). The study shows for the first time that there is not a direct connection between oxygen deficiency and cation disordering. This demonstrates that it is possible to tune disordering in LNMO without inducing oxygen deficiencies or forming the rock-salt impurity phase. Electrochemical testing of samples with different degrees of ordering and oxygen deficiency (i.e. highly ordered, partially ordered and fully disordered) have been performed in LNMO-LTO (Li4Ti5O12) full cells. It was shown that all cells behave similarly during the initial period of cycling even when discharged at 10C rate, however, over time the disordered sample exhibited the best performance.
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| 12. |
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| 13. |
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| 14. |
- Brant, William, et al.
(author)
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Method of producing a sodium iron(II)-hexacyanoferrate(II) material
- 2018
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Patent (pop. science, debate, etc.)abstract
- The present invention relates to a method of producing a sodium iron(ll)- hexacyanoferrate(ll) (Na2-xFe[Fe(CN)6].mH2O), where x is < 0.4) material commonly referred to as Prussian White. The method comprises the steps of acid decomposition of Na4Fe(CN)6.10H2O to a powder of Na2-xFe[Fe(CN)6].mH2O, drying and enriching the sodium content in the Na2-xFe[Fe(CN)6].mH2O powder by mixing the powder with a saturated or supersaturated solution of a reducing agent containing sodium in dry solvent under an inert gas. The steps of acid decomposition and enriching the sodium content are performed under non-hydrothermal conditions.
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| 15. |
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| 16. |
- Brant, William R, et al.
(author)
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A large format in operando wound cell for analysing the structural dynamics of lithium insertion materials
- 2016
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In: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 336, s. 279-285
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Journal article (peer-reviewed)abstract
- This paper presents a large wound cell for in operando neutron diffraction (ND) from which high quality diffraction patterns are collected every 15 min while maintaining conventional electrochemical performance. Under in operando data collection conditions the oxygen atomic displacement parameters (ADPs) and cell parameters were extracted for Li0.18Sr0.66Ti0.5Nb0.5O3. Analysis of diffraction data collected under in situ conditions revealed that the lithium is located on the (0.5 0.5 0) site, corresponding to the 3c Wyckoff position in the cubic perovskite unit cell, after the cell is discharged to I V. When the cell is discharged under potentiostatic conditions the quantity of lithium on this site increases, indicating a potential position where lithium becomes pinned in the thermodynamically stable phase. During this potentiostatic step the oxygen ADPs reduce significantly. On discharge, however, the oxygen ADPs were observed to increase gradually as more lithium is inserted into the structure. Finally, the rate of unit cell expansion changed by similar to 44% once the lithium content approached similar to 0.17 Li per formula unit. A link between lithium content and degree of mobility, disorder of the oxygen positions and changing rate of unit cell expansion at various stages during lithium insertion and extraction is thus presented.
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| 17. |
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| 18. |
- Brant, William R., et al.
(author)
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In Operando X-ray and Neutron Diffraction for Lithium Ion Batteries
- 2017
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Other publication (other academic/artistic)abstract
- To find new materials for lithium-ion batteries (LIBs) or to improve existing materials is a huge field of research. The positive electrode material in these devices is a bottleneck for increasing the energy density for the LIB and numerous oxides, phosphates, and silicates based on transition metals have been suggested. The crystallinity, chemical composition and structure of the bulk and the surface of a potential material are some important parameters influencing battery performance. In this presentation, we will show some examples of iron and Mn/Ni based cathode materials, and how in operando X-ray and neutron diffraction results have contributed to the understanding of how these materials function in batteries. In operando X-ray and neutron diffraction are extremely powerful techniques for investigating reaction mechanisms in battery materials in general. To date, the vast majority of these experiments have been performed using synchrotron X-ray diffraction, predominantly due to the fast data collection times possible. Is it so that synchrotron based X-ray diffraction always is the best choice? We will discuss this and show why in house in operando diffraction still is powerful. In operando neutron diffraction experiments are becoming increasingly popular due to a range of new cell designs increasing the accessibility of the technique [1], [2]. This presentation will discuss two different approaches to in operando neutron diffraction: a larger format wound cell and a cheaper modified a coin type cell. The wound cell design contains a large quantity of active material (up to 4 g) enabling high quality diffraction patterns to be collected down to small d-spacings. When used to investigate the positive electrode material LiMn1.5Ni0.5O4, reflections arising from Mn/Ni ordering could be observed to change during battery cycling. The modified coin cell design utilizes a completely different approach to in operando neutron diffraction experiments. The modified coin cells contain a large quantity of active material (~300-400 mg) to a much smaller amount of electrolyte (~10‑50 μL), separator and lithium metal. The smaller volume of electrolyte is particularly vital as it substantially reduces the cost of the experiment, as deuteration may no longer be necessary. The modified coin cell exhibited favourable electrochemistry when cycled at C/12 and enabled unit cell and phase fraction information to be extracted from in operando data collection conditions (5-15 min data sets). [1] M. Bianchini, E. Suard, L. Croguennec, C. Masquelier, J. Phys. Chem. C, 2014, 118, 25947. [2] R. Petibon, J. Li, N. Sharma, W.K. Pang, V.K. Peterson, J.R. Dahn, Electrochim. Acta, 2015, 174, 417.
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| 19. |
- Brant, William R., et al.
(author)
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Local structure transformations promoting high lithium diffusion in defect perovskite type structures
- 2023
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In: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 441
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Journal article (peer-reviewed)abstract
- Defect perovskites, AxBO3 such as (Li3xLa2/3-x)TiO3, are attracting attention as high capacity electrodes in lithium-ion batteries. However, the mechanism enabling high lithium storage capacities has not been fully investigated. In this work, the reversible insertion and removal of lithium up to an average A-site cavity occupancy of 1.71 in the defect perovskite (Li0.18Sr0.66)(Ti0.5Nb0.5)O3 is investigated. It was shown that subtle lithium reorganization during lithiation has a significant impact on enabling high capacity. Contrary to previous studies, lithium was coordinated to triangular faces of Ti/Nb oxygen octahedra and offset from O4 windows between A-site cavities in the as-synthesised material. Upon electrochemical lithiation Li-Li repulsion redistributes of all the lithium towards the O4 window position resulting in a loss of lithium mobility. Surprisingly, the mobility is regained during over-lithiation and following multiple electrochemical cycles. It is suggested that lithium reorganisation into the center of the O4 window alleviates the Li-Li repulsion and modifies the diffusion behavior from site percolation to bond percolation. The results obtained provide valuable insight into the chemical drivers enabling higher capacities and enhanced diffusion in defect perovskites. More broadly the study delivers fundamental understanding on the non-equilibrium structural transformations occurring within electrode materials during repeated electrochemical cycles.
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| 20. |
- Brant, William R., et al.
(author)
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Rapid Lithium Insertion and Location of Mobile Lithium in the Defect Perovskite Li0.18Sr0.66Ti0.5Nb0.5O3
- 2012
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In: ChemPhysChem. - : Wiley-Blackwell. - 1439-4235 .- 1439-7641. ; 13:9, s. 2293-2296
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Journal article (peer-reviewed)abstract
- Fast and fancy: Lithium that was originally disordered within the structure of the perovskite Li0.18Sr0.66Ti0.5Nb0.5O3 can be induced into ordering within the yellow region of the unit cell by low temperatures and treatment with n-butyl-lithium. The fast kinetics of lithium insertion, in connection with a color change, make this nontoxic, air-stable material a suitable candidate for use in electrochromic systems or lithium-storage batteries.
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