B18-Core EXAFS
I11-High Resolution Powder Diffraction
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[25166, 14239]
Open Access
Abstract: The high natural abundance and low toxicity of iron oxides provide a strong motivation to develop iron-based lithium-ion battery cathode materials. T-LiFeO2 adopts a cation-ordered wurtzite structure consisting of apex-linked LiO4 and FeO4 tetrahedra. Chemical or electrochemical lithium extraction rapidly converts T-LiFeO2 to the spinel LiFe5O8 and leads to poor energy storage performance. We have investigated the role of Al and Ga substitution on the stability of T-LiFeO2. Partial substitution of Fe by Al leads to the formation of cation-disordered solid solutions. In contrast, neutron diffraction data reveal that the Ga-substituted phase LiFe0.5Ga0.5O2 adopts an Fe/Ga cation-ordered structure. Chemical delithiation of LiFe1–xMxO2 phases reveals that 25% Al or 50% Ga substitution stabilizes the T-LiFe1–xMxO2 phases with respect to spinel conversion. The delithiated phases show no evidence of cation migration or oxygen loss. However, Fe-XANES, O-XAS, and O-RIXS data indicate that lithium extraction does not proceed via simple oxidation of Fe3+ to Fe4+ but rather via an anion redox process involving the formation of localized “FeIV–O” centers. Electrochemical data indicate that the formation of FeIV–O centers is irreversible, and so these oxidized species accumulate with continued electrochemical cycling, leading to a rapid decline in energy storage capacity. The electrochemical behavior of LiFe0.5Al0.5O2 and LiFe0.5Ga0.5O2 is discussed in terms of their crystal chemistry to account for the differing electrochemical performance of the Al- and Ga-substituted materials.
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Apr 2025
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B18-Core EXAFS
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Diamond Proposal Number(s):
[11874]
Open Access
Abstract: Li-rich garnet solid electrolytes are promising candidates for all-solid-state batteries, permitting increased energy densities, compatibility with Li-metal anodes and improved safety by replacing flammable organic-based liquid electrolytes. Li-stuffed garnets typically require aliovalent doping to stabilise the highly ionic conductive Ia3 @#x0305;d cubic phase. The role of dopants and their location within the garnet framework can greatly affect the conduction properties of these garnets, yet their impact on structure and resulting ion transport are not fully understood. Here, we evaluate the effect of aliovalent doping with Al3+, Ga3+ and Zn2+ in the Li6BaLa2Ta2O12 (LBLTO) garnet material. A combination of PXRD and XAS reveal a linear cell parameter contraction with increasing doping noted and preference of the 24d Li+ sites for Al3+ and Zn2+ dopants, with Ga3+ occupying both the 24d and 48g Li+ sites. Macroscopic ionic conductivity analyses by EIS demonstrate an enhancement of the transport properties where addition of small amounts of Al3+ decrease the activation energy to Li+ diffusion to 0.35(4) eV. A detrimental effect on ionic conductivities is observed when introducing the dopants onto Li+ pathways and upon decreasing Li+ concentration. Insights into this behaviour are gleaned from microscopic diffusion studies by muon spin relaxation (µ+SR) spectroscopy, which reveal a low activation energy barrier for Li+ diffusion of 0.16(1) eV and a diffusion coefficient comparable to those of the Li7La3Zr2O12 (LLZO) benchmark garnet materials.
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Oct 2024
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B18-Core EXAFS
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Matthew J. W.
Ogley
,
Ashok S.
Menon
,
Gaurav C.
Pandey
,
Galo J.
Paez Fajardo
,
Beth J.
Johnston
,
Innes
Mcclelland
,
Veronika
Majherova
,
Steven
Huband
,
Debashis
Tripathy
,
Israel
Temprano
,
Stefano
Agrestini
,
Veronica
Celorrio
,
Gabriel E.
Perez
,
Samuel G.
Booth
,
Clare P.
Grey
,
Serena A.
Cussen
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[33292, 33173]
Open Access
Abstract: This study refutes the commonly used ionic-bonding model that demarcates transition metal (TM) and oxygen redox using an archetypal Ni-rich layered oxide cathode, LiNi0.8Mn0.1Co0.1O2. Here, charge compensation during delithiation occurs without formal (ionic) Ni oxidation. Instead, oxygen-dominated states control the redox process, facilitated by strong TM-O hybridization, forming bulk-stable 3d8L and 3d8L2 electronic states, where L is a ligand hole. Bulk O–O dimers are observed with O K-edge resonant inelastic X-ray scattering but, critically, without the long-range TM migration or void formation observed in Li-rich layered oxides. Above 4.34 V vs. Li+/Li, the cathode loses O, forming a resistive surface rock-salt layer that causes capacity fade. This highlights the importance of cathode engineering when attempting to achieve higher energy densities with layered oxide cathodes, especially in those where O dominates the charge compensation mechanism.
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Oct 2024
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B18-Core EXAFS
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Matthew
Ogley
,
Ashok S.
Menon
,
Beth J.
Johnston
,
Gaurav
Pandey
,
Innes
Mcclelland
,
Xiaoqun
Shi
,
Stefano
Agrestini
,
Veronica
Celorrio
,
Gabriel E.
Perez
,
Samuel G.
Booth
,
Jordi
Cabana
,
Serena A.
Cussen
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[33292, 33173]
Open Access
Abstract: In layered lithium transition metal oxide cathodes, high-voltage operation is accompanied by the formation of oxygen dimers, which are widely used as an indicator of oxygen-redox activity. However, understanding the role that oxygen dimerization plays in facilitating charge compensation is still needed. Li2NiO3 (a 3d8L2-containing compound, where L is a ligand hole) is studied as a model system, where oxygen dimerization is shown to occur without cathode oxidation. Electrochemical cycling results in a net reduction of the cathode, accompanied by structural transformations, despite spectroscopic features of oxygen dimers arising at the top-of-charge. Here, oxygen dimerization is shown to coexist alongside a structurally transformed and electronically reduced cathode structure, thus highlighting that O dimerization is independent of bulk redox processes. This makes it clear that a thermodynamically derived transformation toward a reduced phase remains the only variable capable of generating O–O dimers in Li2NiO3.
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Aug 2024
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[25166, 14239]
Open Access
Abstract: Li3Fe3Te2O12 adopts a crystal structure, described in space group Pnnm, related to that of LiSbO3, in which Te6+, Fe3+, and Li+ cations reside in a partially ordered configuration within an hcp array of oxide ions. Chemical or electrochemical insertion of lithium is accompanied by a fully reversible migration of some of the Fe cations with an initial capacity of 120 mA h g–1 (2.85 Li per formula unit). Long-term cycling stability is limited by the facile reduction of Te6+ to elemental Te, which leads to cathode decomposition. Partial substitution of Fe by In suppresses Te6+ reduction, such that Li3Fe2InTe2O12 shows no sign of this cathode decomposition pathway, even after 100 cycles. In contrast, Al-for-Fe substitution is chemically limited to Li3Fe2.6Al0.4Te2O12 and appears to have almost no influence on cathode longevity. These features of the Li3Fe3-xMxTe2O12 system are discussed on the basis of a detailed structural analysis performed using neutron and synchrotron X-ray diffraction.
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Jan 2024
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B18-Core EXAFS
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Open Access
Abstract: New and exotic ground states of magnetic materials are highly sought after and are extensively studied for the insights they provide into the thermodynamics of disorder and fundamental magnetic interactions. By controlling the crystal structure of an appropriate magnetic lattice, it is possible to cause the strong magnetic exchange interactions to sum to zero and so be frustrated. Due to the presence of this frustration, the lowest energy configuration that results may be crucially dependent on the tiniest of energy differences between a multitude of states that have (almost) the same energy. The keen interest in these materials arises from the fact that these finely balanced systems offer a way of probing classical or quantum mechanical interactions that are of fundamental importance but are too weak to be observed in non-frustrated systems. Here, we combine local and crystallographic probes of the cation-ordered double perovskite Ba2MnMoO6 that contains a face-centered cubic lattice of S = 5/2 Mn2+ cations. Neutron diffraction measurements below 9.27(7) K indicate that a fourfold degenerate non-collinear antiferromagnetic state exists with almost complete ordering of the Mn2+ spins. Muon spin relaxation measurements provide a local probe of the magnetic fields inside this material over the t1/2 = 2.2 µs lifetime of a muon, indicating a slightly lower Néel transition temperature of 7.9(1) K. The dc susceptibility data do not show the loss of magnetization that should accompany the onset of the antiferromagnetic order; they indicate that a strongly antiferromagnetically coupled paramagnetic state [θ = −73(3) K] persists down to 4 K, at which temperature a weak transition occurs. The behavior of this material differs considerably from the closely related compositions Ba2MnMO6 (M = W, Te), which show collinear ordering arrangements and well defined antiferromagnetic transitions in the bulk susceptibility. This suggests that the Mo6+ cation leads to a fine balance between the nearest and next-nearest neighbor superexchange in these frustrated double perovskite structures.
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May 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Samuel W.
Coles
,
Viktoria
Falkowski
,
Harry S.
Geddes
,
Gabriel E.
Pérez
,
Samuel G.
Booth
,
Alexander G.
Squires
,
Conn
O'Rourke
,
Kit
Mccoll
,
Andrew L.
Goodwin
,
Serena A.
Cussen
,
Simon J.
Clarke
,
Saiful
Islam
,
Benjamin J.
Morgan
Diamond Proposal Number(s):
[27702]
Open Access
Abstract: Short-range ordering in cation-disordered cathodes can have a significant effect on their electrochemical properties. Here, we characterise the cation short-range order in the antiperovskite cathode material Li2FeSO, using density functional theory, Monte Carlo simulations, and synchrotron X-ray pair-distribution-function data. We predict partial short-range cation-ordering, characterised by favourable OLi4Fe2 oxygen coordination with a preference for polar cis-OLi4Fe2 over non-polar trans-OLi4Fe2 configurations. This preference for polar cation configurations produces long-range disorder, in agreement with experimental data. The predicted short-range-order preference contrasts with that for a simple point-charge model, which instead predicts preferential trans-OLi4Fe2 oxygen coordination and corresponding long-range crystallographic order. The absence of long-range order in Li2FeSO can therefore be attributed to the relative stability of cis-OLi4Fe2 and other non-OLi4Fe2 oxygen-coordination motifs. We show that this effect is associated with the polarisation of oxide and sulfide anions in polar coordination environments, which stabilises these polar short-range cation orderings. We propose similar anion-polarisation–directed short-range-ordering may be present in other heterocationic materials that contain cations with different formal charges. Our analysis also illustrates the limitations of using simple point-charge models to predict the structure of cation-disordered materials, where other factors, such as anion polarisation, may play a critical role in directing both short- and long-range structural correlations.
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Apr 2023
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I09-Surface and Interface Structural Analysis
I21-Resonant Inelastic X-ray Scattering (RIXS)
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A. S.
Menon
,
B. J.
Johnston
,
S. G.
Booth
,
L.
Zhang
,
K.
Kress
,
B. E.
Murdock
,
G.
Paez Fajardo
,
N. N.
Anthonisamy
,
N.
Tapia-Ruiz
,
S.
Agrestini
,
M.
Garcia-Fernandez
,
K.
Zhou
,
P. K.
Thakur
,
T. L.
Lee
,
A. J.
Nedoma
,
S. A.
Cussen
,
L. F. J.
Piper
Diamond Proposal Number(s):
[29104, 29113]
Open Access
Abstract: The desire to increase the energy density of stoichiometric layered
Li
TM
O
2
(TM = 3d transition metal) cathode materials has promoted investigation into their properties at high states of charge. Although there is increasing evidence for pronounced oxygen participation in the charge compensation mechanism, questions remain whether this is true
O
-redox, as observed in
Li
-excess cathodes. Through a high-resolution
O
K-edge resonant inelastic x-ray spectroscopy (RIXS) study of the
Mn
-free
Ni
-rich layered oxide
Li
Ni
0.98
W
0.02
O
2
, we demonstrate that the same oxidized oxygen environment exists in both
Li
-excess and non-
Li
-excess systems. The observation of identical RIXS loss features in both classes of compounds is remarkable given the differences in their crystallographic structure and delithiation pathways. This lack of a specific structural motif reveals the importance of electron correlation in the charge compensation mechanism for these systems and indicates how a better description of charge compensation in layered oxides is required to understand anionic redox for energy storage.
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Mar 2023
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B18-Core EXAFS
I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[25166]
Open Access
Abstract: Cation migration on electrochemical cycling can significantly influence the performance of li-ion cathode materials. Phases of composition LiFe2–xInxSbO6 (0 < x <1) adopt crystal structures described in space group Pnnm, consisting of a hexagonally close-packed array of oxide ions, with Fe/In and Sb cations ordered on octahedral sites, and lithium cations located within partially occupied tetrahedral sites. NPD, SXRD, and 57Fe Mössbauer data indicate that on reductive lithium insertion (either chemically or electrochemically), LiFe2SbO6 is converted to Li2Fe2SbO6 accompanied by large-scale cation migration, to form a partially Fe/Li cation-ordered and Fe2+/Fe3+ charge-ordered phase from which lithium cations cannot be easily removed, either chemically or electrochemically. Partial substitution of Fe with In suppresses the degree of cation migration that occurs on lithium insertion such that no structural change is observed when LiFeInSbO6 is converted into Li1.5FeInSbO6, allowing the system to be repeatedly electrochemically cycled between these two compositions. Phases with intermediate levels of In substitution exhibit low levels of Fe migration on Li insertion and electrochemical capacities which evolve on cycling. The mechanism by which the In3+ cations suppress the migration of Fe cations is discussed along with the cycling behavior of the LiFe1.5In0.5SbO6–Li1.75Fe1.5In0.5SbO6.
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Dec 2022
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[25542]
Open Access
Abstract: The realisation of post-combustion CO2 capture (PCCC) at industrial scale remains limited; one challenge is the concerns around capital costs and another concern is corrosion of the system itself. Corrosion resistance and mitigation against the amine solvent monoethanolamine (MEA) was studied, using the inhibitor copper (II) carbonate basic (CC). Carbon steel (C1018) was tested in CO2 loaded, 5M aqueous MEA solution, alone and in the presence of CC, to assess the corrosivity of the solution. Immersion testing used mass loss, Fe and Cu ion concentration in solution via ICP-MS, imaging (SEM) and analytical techniques (XRD and EDX) to investigate the effect of corrosion. Generally, the use of CC improved C1018 corrosion resistance relative to C1018 alone. Even at low concentrations (0.9 mM), CC was effective in inhibiting corrosion against CO2 loaded MEA, as the observed corrosion rate was effectively zero and no dissolved Fe was detected in solution. There was no evidence of copper surface adsorption. To clarify the solution chemistry resulting in corrosion inhibition, the local chemical environment of Fe and Cu were probed by Cu and Fe K-edge X-ray Absorption Spectroscopy, respectively. The Cu K- edge HERFD-XANES spectra reveal that a Cu2+ amine complex forms, critical to understanding the structure which is promoting significant corrosion inhibition.
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Dec 2022
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