B18-Core EXAFS
|
Diamond Proposal Number(s):
[14239]
Open Access
Abstract: Optimisation of electrodeposition routes of birnessite manganese dioxide (MnO2) coatings onto 3D graphene foam substrates enabled greater attainable capacitances. Current pulse deposition method resulted in highest achievable areal capacitance of 530 mF/cm2 under a 10 mA/cm2 current rate, cycling performance with 91% retention after 9000 cycles, as well as improved rate capability when compared to the cyclic voltammetry or galvanostatic deposition. Introduction of oxygen functional groups to the graphene foam added initial pseudocapacitance and accelerated the rate for nucleation and growth of the MnO2 crystal grains, resulting in an areal capacitance of 410 mF/cm2 under a 10 mA/cm2 current rate. However, in this case the increase in specific capacitance was accompanied by sluggish kinetic for charge storage seen via impedance spectroscopy. The charge storage mechanism of the deposited MnO2 films was investigated using in situ Raman microscopy and analysis of peak shifts revealed expansion and contraction of birnessite MnO2, relating to exchange of Na+ and H2O at the MnO2 interface.
|
Apr 2023
|
|
I09-Surface and Interface Structural Analysis
|
Leanne A. H.
Jones
,
Zongda
Xing
,
Jack E. N.
Swallow
,
Huw
Shiel
,
Thomas J.
Featherstone
,
Matthew J.
Smiles
,
Nicole
Fleck
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Laurence J.
Hardwick
,
David O.
Scanlon
,
Anna
Regoutz
,
Tim D.
Veal
,
Vinod R.
Dhanak
Diamond Proposal Number(s):
[25980]
Open Access
Abstract: A comprehensive study of bulk molybdenum dichalcogenides is presented with the use of soft and hard X-ray photoelectron (SXPS and HAXPES) spectroscopy combined with hybrid density functional theory (DFT). The main core levels of MoS2, MoSe2, and MoTe2 are explored. Laboratory-based X-ray photoelectron spectroscopy (XPS) is used to determine the ionization potential (IP) values of the MoX2 series as 5.86, 5.40, and 5.00 eV for MoSe2, MoSe2, and MoTe2, respectively, enabling the band alignment of the series to be established. Finally, the valence band measurements are compared with the calculated density of states which shows the role of p-d hybridization in these materials. Down the group, an increase in the p-d hybridization from the sulfide to the telluride is observed, explained by the configuration energy of the chalcogen p orbitals becoming closer to that of the valence Mo 4d orbitals. This pushes the valence band maximum closer to the vacuum level, explaining the decreasing IP down the series. High-resolution SXPS and HAXPES core-level spectra address the shortcomings of the XPS analysis in the literature. Furthermore, the experimentally determined band alignment can be used to inform future device work.
|
Dec 2022
|
|
B18-Core EXAFS
I11-High Resolution Powder Diffraction
I15-1-X-ray Pair Distribution Function (XPDF)
|
Diamond Proposal Number(s):
[23666, 23167]
Open Access
Abstract: Li-rich rocksalt oxides are promising candidates as high-energy density cathode materials for next-generation Li-ion batteries because they present extremely diverse structures and compositions. Most reported materials in this family contain as many cations as anions, a characteristic of the ideal cubic closed-packed rocksalt composition. In this work, a new rocksalt-derived structure type is stabilized by selecting divalent Cu and pentavalent Sb cations to favor the formation of oxygen vacancies during synthesis. The structure and composition of the oxygen-deficient Li4CuSbO5.5□0.5 phase is characterized by combining X-ray and neutron diffraction, ICP-OES, XAS, and magnetometry measurements. The ordering of cations and oxygen vacancies is discussed in comparison with the related Li2CuO2□1 and Li5SbO5□1 phases. The electrochemical properties of this material are presented, with only 0.55 Li+ extracted upon oxidation, corresponding to a limited utilization of cationic and/or anionic redox, whereas more than 2 Li+ ions can be reversibly inserted upon reduction to 1 V vs Li+/Li, a large capacity attributed to a conversion reaction and the reduction of Cu2+ to Cu0. Control of the formation of oxygen vacancies in Li-rich rocksalt oxides by selecting appropriate cations and synthesis conditions affords a new route for tuning the electrochemical properties of cathode materials for Li-ion batteries. Furthermore, the development of material models of the required level of detail to predict phase diagrams and electrochemical properties, including oxygen release in Li-rich rocksalt oxides, still relies on the accurate prediction of crystal structures. Experimental identification of new accessible structure types stabilized by oxygen vacancies represents a valuable step forward in the development of predictive models.
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Dec 2021
|
|
I19-Small Molecule Single Crystal Diffraction
|
Guopeng
Han
,
Andrij
Vasylenko
,
Alex R.
Neale
,
Benjamin B.
Duff
,
Ruiyong
Chen
,
Matthew S.
Dyer
,
Yun
Dang
,
Luke
Daniels
,
Marco
Zanella
,
Craig
Robertson
,
Laurence J.
Kershaw Cook
,
Anna-Lena
Hansen
,
Michael
Knapp
,
Laurence J.
Hardwick
,
Frédéric
Blanc
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Diamond Proposal Number(s):
[21726]
Open Access
Abstract: Extended anionic frameworks based on condensation of polyhedral main group non-metal anions offer a wide range of structure types. Despite the widespread chemistry and earth abundance of phosphates and silicates, there are no reports of extended ultraphosphate anions with lithium. We describe the lithium ultraphosphates Li3P5O14 and Li4P6O17 based on extended layers and chains of phosphate, respectively. Li3P5O14 presents a complex structure containing infinite ultraphosphate layers with 12-membered rings that are stacked alternately with lithium polyhedral layers. Two distinct vacant tetrahedral sites were identified at the end of two distinct finite Li6O1626– chains. Li4P6O17 features a new type of loop-branched chain defined by six PO43– tetrahedra. The ionic conductivities and electrochemical properties of Li3P5O14 were examined by impedance spectroscopy combined with DC polarization, NMR spectroscopy, and galvanostatic plating/stripping measurements. The structure of Li3P5O14 enables three-dimensional lithium migration that affords the highest ionic conductivity (8.5(5) × 10–7 S cm–1 at room temperature for bulk), comparable to that of commercialized LiPON glass thin film electrolytes, and lowest activation energy (0.43(7) eV) among all reported ternary Li–P–O phases. Both new lithium ultraphosphates are predicted to have high thermodynamic stability against oxidation, especially Li3P5O14, which is predicted to be stable to 4.8 V, significantly higher than that of LiPON and other solid electrolytes. The condensed phosphate units defining these ultraphosphate structures offer a new route to optimize the interplay of conductivity and electrochemical stability required, for example, in cathode coatings for lithium ion batteries.
|
Oct 2021
|
|
I11-High Resolution Powder Diffraction
|
Andrij
Vasylenko
,
Jacinthe
Gamon
,
Benjamin B.
Duff
,
Vladimir V.
Gusev
,
Luke M.
Daniels
,
Marco
Zanella
,
J. Felix
Shin
,
Paul M.
Sharp
,
Alexandra
Morscher
,
Ruiyong
Chen
,
Alex R.
Neale
,
Laurence J.
Hardwick
,
John B.
Claridge
,
Frédéric
Blanc
,
Michael W.
Gaultois
,
Matthew S.
Dyer
,
Matthew J.
Rosseinsky
Diamond Proposal Number(s):
[23666]
Open Access
Abstract: The selection of the elements to combine delimits the possible outcomes of synthetic chemistry because it determines the range of compositions and structures, and thus properties, that can arise. For example, in the solid state, the elemental components of a phase field will determine the likelihood of finding a new crystalline material. Researchers make these choices based on their understanding of chemical structure and bonding. Extensive data are available on those element combinations that produce synthetically isolable materials, but it is difficult to assimilate the scale of this information to guide selection from the diversity of potential new chemistries. Here, we show that unsupervised machine learning captures the complex patterns of similarity between element combinations that afford reported crystalline inorganic materials. This model guides prioritisation of quaternary phase fields containing two anions for synthetic exploration to identify lithium solid electrolytes in a collaborative workflow that leads to the discovery of Li3.3SnS3.3Cl0.7. The interstitial site occupancy combination in this defect stuffed wurtzite enables a low-barrier ion transport pathway in hexagonal close-packing.
|
Sep 2021
|
|
B18-Core EXAFS
I11-High Resolution Powder Diffraction
|
Jacinthe
Gamon
,
Arnaud J.
Perez
,
Leanne A. H.
Jones
,
Marco
Zanella
,
Luke M.
Daniels
,
Rhun E.
Morris
,
Chiu C.
Tang
,
Tim
Veal
,
Laurence J.
Hardwick
,
Matthew S
Dyer
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Open Access
Abstract: Multiple anion materials are of particular interest for the discovery of new crystal structures and offer an original way to modulate physical properties, including energy storage materials with enhanced performances. Through careful synthesis optimization, a new Na2Fe2OS2 phase was prepared by two different routes: high temperature solid-state synthesis and simple mechanochemical synthesis. The long-range and local structure of Na2Fe2OS2 was studied by Rietveld refinement of neutron and X-ray diffraction data combined with EXAFS data refinement. The phase comprises an amorphous and a crystalline part which has an anti-K2NiF4 structure, corresponding to the n = 1 member of the homologous anti-Ruddlesden-Popper [AX][ABX3]n series. Its electrochemical properties as a cathode material were studied in Na half cells and Na-ion full cells, revealing that the material becomes fully amorphous upon initial desodiation to Na0.5Fe2OS2, but maintains a reversible capacity of 135 mAh·g-1 in full cells where up to 1.2 Na+ can be reversibly extracted and reinserted when compensating for the Na lost in SEI formation. The stability of the pristine material and its structural evolution upon charging are discussed, paving the way for further optimization of this material. Being composed exclusively of earth-abundant elements and stable under dry air, Na2Fe2OS2 perfectly illustrates the great opportunity of multiple anion chemistry to explore new structure types and develop better energy storage systems.
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Sep 2020
|
|
I09-Surface and Interface Structural Analysis
|
Leanne A. H.
Jones
,
Wojciech M.
Linhart
,
Nicole
Fleck
,
Jack E. N.
Swallow
,
Philip A. E.
Murgatroyd
,
Huw
Shiel
,
Thomas J.
Featherstone
,
Matthew J.
Smiles
,
Pardeep K.
Thakur
,
Tien-Lin
Lee
,
Laurence J.
Hardwick
,
Jonathan
Alaria
,
Frank
Jaeckel
,
Robert
Kudrawiec
,
Lee A.
Burton
,
Aron
Walsh
,
Jonathan M.
Skelton
,
Tim D.
Veal
,
Vin R.
Dhanak
Diamond Proposal Number(s):
[21431]
Open Access
Abstract: The effects of Sn
5
s
lone pairs in the different phases of Sn sulphides are investigated with photoreflectance, hard x-ray photoemission spectroscopy (HAXPES), and density functional theory. Due to the photon energy-dependence of the photoionization cross sections, at high photon energy, the Sn
5
s
orbital photoemission has increased intensity relative to that from other orbitals. This enables the Sn
5
s
state contribution at the top of the valence band in the different Sn-sulphides, SnS,
Sn
2
S
3
, and
SnS
2
, to be clearly identified. SnS and
Sn
2
S
3
contain Sn(II) cations and the corresponding Sn
5
s
lone pairs are at the valence band maximum (VBM), leading to
∼
1.0
–1.3 eV band gaps and relatively high VBM on an absolute energy scale. In contrast,
SnS
2
only contains Sn(IV) cations, no filled lone pairs, and therefore has a
∼
2.3
eV room-temperature band gap and much lower VBM compared with SnS and
Sn
2
S
3
. The direct band gaps of these materials at 20 K are found using photoreflectance to be 1.36, 1.08, and 2.47 eV for SnS,
Sn
2
S
3
, and
SnS
2
, respectively, which further highlights the effect of having the lone-pair states at the VBM. As well as elucidating the role of the Sn
5
s
lone pairs in determining the band gaps and band alignments of the family of Sn-sulphide compounds, this also highlights how HAXPES is an ideal method for probing the lone-pair contribution to the density of states of the emerging class of materials with
n
s
2
configuration.
|
Jul 2020
|
|
B18-Core EXAFS
I11-High Resolution Powder Diffraction
|
Zoe N.
Taylor
,
Arnaud J.
Perez
,
Jose A.
Coca-Clemente
,
Filipe
Braga
,
Nicholas E.
Drewett
,
Michael J.
Pitcher
,
William J.
Thomas
,
Matthew S.
Dyer
,
Christopher
Collins
,
Marco
Zanella
,
Timothy
Johnson
,
Sarah
Day
,
Chiu
Tang
,
Vinod R
Dhanak
,
John B.
Claridge
,
Laurence J.
Hardwick
,
Matthew J.
Rosseinsky
Abstract: Multinary lithium oxides with the rock salt structure are of technological importance as cathode materials in rechargeable lithium ion batteries. Current state of the art cathodes such as LiNi1/3Mn1/3Co1/3O2 rely on redox cycling of earth-abundant transition metal cations to provide charge capacity. Recently, the possibility of using the oxide anion as a redox center in Li-rich rock salt oxides has been established as a new paradigm in the design of cathode materials with enhanced capacities (> 200 mAh/g). To increase the lithium content and access electrons from oxygen-derived states, these materials typically require transition metals in high oxidation states, which can be easily achieved using d0 cations. However, Li-rich rocksalt oxides with high valent d0 cations such as Nb5+ and Mo6+ show strikingly high voltage hysteresis between charge and discharge, the origin of which is uninvestigated. In this work, we study a series of Li-rich compounds, Li4+xNi1-xWO6 (0 ≤ x ≤ 0.25), adopting two new and distinct cation-ordered variants of the rock salt structure. The phase Li4.15Ni0.85WO6 (x = 0.15) has a large reversible capacity of 200 mAh/g, without accessing the Ni3+/Ni4+ redox couple, implying that over two-thirds of the capacity is due to anionic redox, with good cyclability. The presence of the 5d0 W6+ cation affords extensive (> 2 V) voltage hysteresis associated with the anionic redox. We present experimental evidence for the formation of strongly stabilized localized O-O single bonds that explain the energy penalty required to reduce the material upon discharge. The high valent d0 cation associates localized anion-anion bonding with the anion redox capacity.
|
Apr 2019
|
|
I07-Surface & interface diffraction
|
Diamond Proposal Number(s):
[9850]
Abstract: In situ electrochemical surface X-ray diffraction was employed to investigate the atomic scale structure of the electrochemical double layer and the relaxation at the Pt(111) electrode surface in non-aqueous and aqueous acetonitrile electrolytes under potential control. The X-ray measurements provide insight into the potential-dependence of the interface structure by combining potentiodynamic measurements (X-ray voltammetry) with potentiostatic measurements (crystal truncation rod data) to probe both the metal and electrolyte sides of the interface. The crystal truncation rod measurements are consistent with the potential dependent reorientation of acetonitrile in the absence of water and a parallel arrangement in the presence of water. As acetonitrile concentration increases, the electron density closest to the electrode surface also increases. Finally, Pt surface relaxation in a range of aqueous and non-aqueous solvents is discussed in general with regards to the structure of the electrochemical double layer.
|
Feb 2019
|
|
I11-High Resolution Powder Diffraction
|
Bernhard T.
Leube
,
Kenneth K.
Inglis
,
Elliot
Carrington
,
Paul M.
Sharp
,
J. Felix
Shin
,
Alex R.
Neale
,
Troy D.
Manning
,
Michael J.
Pitcher
,
Laurence
Hardwick
,
Matthew S.
Dyer
,
Frédéric
Blanc
,
John B.
Claridge
,
Matthew J.
Rosseinsky
Open Access
Abstract: In order to understand the structural and compositional factors controlling lithium transport in sulfides, we explored the Li5AlS4 – Li4GeS4 phase field for new materials. Both parent compounds are defined structurally by a hexagonal close packed sulfide lattice, where distinct arrangements of tetrahedral metal sites give Li5AlS4 a layered structure and Li4GeS4 a three dimensional structure related to γ-Li3PO4. The combination of the two distinct structural motifs is expected to lead to new structural chemistry. We identified the new crystalline phase Li4.4Al0.4Ge0.6S4, and investigated the structure and Li+ ion dynamics of the family of structurally related materials Li4.4M0.4M’0.6S4 (M = Al3+, Ga3+ and M’= Ge4+, Sn4+). We used neutron diffraction to solve the full structures of the Al-homologues, which adopt a layered close-packed structure with a new arrangement of tetrahedral (M/M’) sites and a novel combination of ordered and disordered lithium vacancies. AC impedance spectroscopy revealed lithium conductivities in the range 3(2) x 10-6 to 4.3(3) x 10-5 S cm-1 at room temperature with activation energies between 0.43(1) and 0.38(1) eV. Electrochemical performance was tested in a plating and stripping experiment against Li metal electrodes and showed good stability of the Li4.4Al0.4Ge0.6S4 phase over 200 hours. A combination of variable temperature 7Li solid state nuclear magnetic resonance spectroscopy and ab initio molecular dynamics calculations on selected phases showed that two dimensional diffusion with a low energy barrier of 0.17 eV is responsible for long-range lithium transport, with diffusion pathways mediated by the disordered vacancies while the ordered vacancies do not contribute to the conductivity. This new structural family of sulfide Li+ ion conductors offers insight into the role of disordered vacancies on Li+ ion conductivity mechanisms in hexagonally close packed sulfides that can inform future materials design.
|
Sep 2018
|
|
