E01-JEM ARM 200CF
E02-JEM ARM 300CF
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Abstract: his thesis sets out to improve the understanding and development of sodium ion battery cathode materials. The thesis focuses on layered metal oxides across a range of compositions and seeks to develop models of the atomic structure that are more expressive of the actual systems than the currently accepted approaches. In doing this multi-modal structural studies will be used, leveraging the individual advantages of Electron, X-ray and Neutron diffraction to produce a more complete model of the physical structures.
The use of cutting-edge electron diffraction techniques which produce vast quantities of data, lead to the development of a novel semi-autonomous data-processing workflow, that is widely applicable to many material systems, not just battery cathode materials. This workflow is documented and investigated across a range of use cases, as well as being applied in the subsequent cathode studies.
The electron diffraction workflow is used in conjunction with other complementary diffraction approaches, as well as pure computational studies, to develop atomic models for the series of cathode structures. The structural models developed provide a better fit to the experimental data gathered than the currently accepted models and identify a novel intra-layer sodium ion ordering scheme that has not been observed in the literature. Additionally the models express further ionic orderings, both intra-layer and inter-layer, that are supported by the experimental evidence and identify structural nuances which will effect battery performance, but are overlooked by current models.
Finally, a methodology for studying oxidation state of Mn at a near atomic resolution level is discussed, with the workflow applied to the cathode material samples and the results tying into the insights of the structural models developed in the earlier chapters.
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Dec 2024
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B23-Circular Dichroism
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Diamond Proposal Number(s):
[30198]
Open Access
Abstract: The nanoscale chiral arrangement in a bicomponent organic material system comprising donor and acceptor small molecules is shown to depend on the thickness of a film that is responsive to chiral light in an optoelectronic device. In this bulk heterojunction, a previously unreported chiral bis(diketopyrrolopyrrole) derivative was combined with an achiral non-fullerene acceptor. The optical activity of the chiral compound is dramatically different in the pure material and the composite, showing how the electron acceptor influences the donor’s arrangement compared with the pure molecule. Mueller matrix polarimetric imaging shows the authenticity of this effect and the homogeneity of short range chiral orientations between the molecules, as well as more heterogeneous short and longer range arrangements in the films observed in linear dichroic and birefringent effects. The two-dimensional circular dichroism (CD) maps and spectra show the uniformity of the short range supramolecular interactions both in spun-cast films on quartz and blade-coated films on photovoltaic device substrates, where evidence for the chiral arrangement is uniquely provided by the synchrotron CD measurements. The external quantum efficiency of the devices depends upon the handedness of the light used to excite them and the film thickness, that influences the supramolecular arrangement and organization in the film, and determines the selectivity for left or right circularly polarised light. The difference in external quantum efficiency of the photovoltaic devices between the two handedness’ of light correlates with the apparent differential absorbance (g-factor) of the films.
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Dec 2024
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[8699]
Open Access
Abstract: The mechanisms contributing to the electromechanical response of piezoelectric ceramics in shear mode have been investigated using high energy synchrotron x-ray diffraction. Soft lead zirconate titanate ceramic specimens were subjected to an electric field in the range 0.2 to 3.0 MV m-1, perpendicular to that of the initial poling direction, while XRD patterns were recorded in transmission. At low electric field levels, the axial strains remained close to zero but a significant shear strain occurred due to the reversible shear-mode piezoelectric coefficient. Both the axial and shear strains increased substantially at higher field levels due to irreversible ferroelectric domain switching. Eventually, the shear strain decreased again as the average remanent polarization became oriented towards the electric field direction. The lattice strain and domain orientation distributions follow the form of the total strain tensor, enabling the domain switching processes to be monitored by the rotation of the principal strain axis. Reorientation of this axis towards the electric field direction occurred progressively above 0.6 MV m-1, while the angle of rotation increased from 0° to approximately 80° at the maximum field of 3.0 MV m-1. A strong correlation was established between the effective strains associated with different crystallographic directions, which was attributed to the effects of elastic coupling between grains in the polycrystal.
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Nov 2024
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Gukhyun
Lim
,
Min Kyung
Cho
,
Jaewon
Choi
,
Ke-Jin
Zhou
,
Dongki
Shin
,
Seungyun
Jeon
,
Minhyung
Kwon
,
A-Re
Jeon
,
Jinkwan
Choi
,
Seok Su
Sohn
,
Minah
Lee
,
Jihyun
Hong
Abstract: Exploiting oxygen anion redox in Li-/Mn-rich layered oxides (LMR-NMCs) offers the highest capacity among cathode materials for Li-ion batteries (LIBs). However, its long-term utilization is challenging due to continuous voltage and capacity decay caused by irreversible phase transitions involving cation disordering and oxygen release. While extensive studies have revealed the thermodynamic origin of cation disordering, the mechanisms of oxygen loss and consequent lattice densification remain elusive. Moreover, mixed spinel-rocksalt nanodomains formed after cycling complicate the degradation mechanism. Herein, we reveal a strong correlation between phase transition pathways and oxygen stability at the particle surface in LMR-NMCs through a comparative study using electrolyte modification. By tailoring surface reconstruction pathways, we control the overall phase and electrochemistry evolution mechanisms. Removing polar ethylene carbonate from the electrolyte significantly suppresses irreversible oxygen loss at the cathode–electrolyte interface, preferentially promoting the in situ layered-to-spinel phase transition while avoiding typical rocksalt phase formation. The in situ formed spinel-stabilized surface enhances charge transfer kinetics through three-dimensional ion channels, maintaining reversible Ni, Mn, and O redox capability over 700 cycles, as revealed by electron microscopy, X-ray absorption spectroscopy, and resonant inelastic X-ray scattering. Deep delithiation and lithiation enabled by the surface spinel phase accelerate the bulk layered-to-spinel phase transition, inducing thermodynamic voltage fade without capacity loss. Conversely, conventional electrolytes induce layered-to-rocksalt surface reconstruction, impeding charge transfer reactions, which causes simultaneous capacity and (apparent) voltage fades. Our work decouples thermodynamic and kinetic aspects of voltage decay in LMR-NMCs, establishing the correlation between surface reconstruction, bulk phase transition, and the electrochemistry of high-capacity cathodes that exploit cation and anion redox couples. This study highlights the significance of electrochemical interface stabilization for advancing Mn-rich cathode chemistries in future LIBs.
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Nov 2024
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I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[31552, 33389]
Abstract: A set of polar rod-shaped liquid crystalline molecules with large dipole moments (µ > 10.4-14.8 D), their molecular structures based on the ferroelectric nematic prototype DIO, are designed, synthesized, and investigated. When the penultimate fluoro-phenyl ring is replaced by phenylpyrimidine moiety, the molecular dipole moment increases from 9.4 D for DIO to 10.4 D for the new molecule and when the terminal fluoro- group is additionally replaced by the nitrile group, the dipole moment rises to 14.8 D. Such a replacement enhances not only the net dipole moment of the molecule, but it also reduces the steric hindrance to rotations of the moieties within the molecule. The superparaelectric nematic (N) and smectic A (SmA) phases of these compounds are found to exhibit colossal dielectric permittivity, obtained both from dielectric spectroscopy, and capacitance measurements using a simple capacitor divider circuit. The electric polarization is measured vs. the field (E). However, no hysteresis in P vs. E is found in the nematic and smectic A phases. The colossal dielectric permittivity persists over the entire fluidic range. The experimental results lead us to conclude that these materials belong to the class of superparaelectrics (SP) rather than to ferroelectrics. The frequency dependence of the threshold voltage for Freedericksz transition qualitatively matches with the square root of the measured dielectric permittivity. Such an agreement validates the frequency dependence of the dielectric permittivity. The synthesized organic materials are the first fluids for which superparaelectricity is discovered and furthermore these materials show great potential for applications in supercapacitors used in storing energy.
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Nov 2024
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B07-B1-Versatile Soft X-ray beamline: High Throughput ES1
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Namrata
Ramesh
,
Hrishit
Banerjee
,
Jack E. N.
Swallow
,
Erik
Bjorklund
,
Ava
Dean
,
Prvanin
Didwal
,
Michael
Fraser
,
Conor M. E.
Phelan
,
Lijin
An
,
Jasper
Singh
,
Jarrod
Lewis
,
Weixin
Song
,
Robert A.
House
,
Andrew J.
Morris
,
Robert S.
Weatherup
,
Rebecca J.
Nicholls
Diamond Proposal Number(s):
[33283]
Open Access
Abstract: Core loss spectroscopies can provide powerful element-specific insight into the redox processes occurring in Li-ion battery cathodes, but this requires an accurate interpretation of the spectral features. Here, we systematically interpret oxygen K-edge core loss spectra of layered lithium transition-metal (TM) oxides (LiMO2, where M = Co, Ni, Mn) from first principles using density-functional theory (DFT). Spectra are simulated using three exchange–correlation functionals, comprising the generalized gradient approximation (GGA) functional PBE, the DFT–PBE + Hubbard U method, and the meta-GGA functional rSCAN. In general, rSCAN provides a better match to experimentally observed excitation energies of spectral features compared to both PBE and PBE + U, especially at energies close to the main edge. Projected density of states of core-hole calculations show that the O orbitals are better described by rSCAN. Hybridization, structural distortions, chemical composition, and magnetism significantly influence the spectra. The O K-edge spectrum of LiNiO2 obtained using rSCAN shows a closer match to the experimental X-ray absorption spectroscopy (XAS) when derived from a simulation cell which includes a Jahn–Teller distortion, showing that the DFT-calculated pre-edge feature contains information about not only chemical species but also geometric distortion. Core loss spectra derived from DFT can also differentiate between materials with the same structure and magnetic configuration but comprising different TMs; these differences are comparable to those observed in experimental XAS from the same materials. This foundational work helps establish the extent to which DFT can be used to bridge the interpretation gap between experimental spectroscopic signatures and ab initio methods describing complex battery materials, such as lithium nickel manganese cobalt oxides.
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Nov 2024
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[35560]
Open Access
Abstract: Nanofibrous active layers offer hierarchical control over molecular structure, and the size and distribution of electron donor:acceptor domains, beyond conventional organic photovoltaic architectures. This structure is created by forming donor pathways via electrospinning nanofibers of semiconducting polymer, then infiltrating with an electron acceptor. Electrospinning induces chain and crystallite alignment, resulting in enhanced light-harvesting and charge transport. Here, the charge transport capabilities are predicted, and charge separation and dynamics are evaluated in these active layers, to assess their photovoltaic potential. Through X-ray and electron diffraction, the fiber nanostructure is elucidated, with uniaxial elongation of the electrospinning jet aligning the polymer backbones within crystallites orthogonal to the fiber axis, and amorphous chains parallel. It is revealed that this structure forms when anisotropic crystallites, pre-assembled in solution, become oriented along the fiber– a configuration with high charge transport potential. Competitive dissociation of excitons formed in the photoactive nanofibers is recorded, with 95%+ photoluminescence quenching upon electron acceptor introduction. Transient absorption studies reveal that silver nanoparticle addition to the fibers improves charge generation and/or lifetimes. 1 ns post-excitation, the plasmonic architecture contains 45% more polarons, per exciton formed, than the bulk heterojunction. Therefore, enhanced exciton populations may be successfully translated into additional charge carriers.
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Nov 2024
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I12-JEEP: Joint Engineering, Environmental and Processing
I13-2-Diamond Manchester Imaging
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Diamond Proposal Number(s):
[26060, 30683, 28773]
Abstract: How advanced X-ray techniques reveal the mechanical factors that shape dendrite growth
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Nov 2024
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I07-Surface & interface diffraction
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Benjamin M.
Gallant
,
Philippe
Holzhey
,
Joel A.
Smith
,
Saqlain
Choudhary
,
Karim A.
Elmestekawy
,
Pietro
Caprioglio
,
Igal
Levine
,
Alexandra A.
Sheader
,
Esther Y.-H.
Hung
,
Fengning
Yang
,
Daniel T. W.
Toolan
,
Rachel C.
Kilbride
,
Karl-Augustin
Zaininger
,
James M.
Ball
,
M. Greyson
Christoforo
,
Nakita K.
Noel
,
Laura M.
Herz
,
Dominik J.
Kubicki
,
Henry J.
Snaith
Diamond Proposal Number(s):
[33462]
Open Access
Abstract: Perovskite solar cells (PSCs) offer an efficient, inexpensive alternative to current photovoltaic technologies, with the potential for manufacture via high-throughput coating methods. However, challenges for commercial-scale solution-processing of metal-halide perovskites include the use of harmful solvents, the expense of maintaining controlled atmospheric conditions, and the inherent instabilities of PSCs under operation. Here, we address these challenges by introducing a high volatility, low toxicity, biorenewable solvent system to fabricate a range of 2D perovskites, which we use as highly effective precursor phases for subsequent transformation to α-formamidinium lead triiodide (α-FAPbI3), fully processed under ambient conditions. PSCs utilising our α-FAPbI3 reproducibly show remarkable stability under illumination and elevated temperature (ISOS-L-2) and “damp heat” (ISOS-D-3) stressing, surpassing other state-of-the-art perovskite compositions. We determine that this enhancement is a consequence of the 2D precursor phase crystallisation route, which simultaneously avoids retention of residual low-volatility solvents (such as DMF and DMSO) and reduces the rate of degradation of FA+ in the material. Our findings highlight both the critical role of the initial crystallisation process in determining the operational stability of perovskite materials, and that neat FA+-based perovskites can be competitively stable despite the inherent metastability of the α-phase.
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Nov 2024
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Mingyuan
Ye
,
Ziqi
Zhao
,
Liying
Liu
,
Li
Shao
,
Li
Liu
,
Xiaorui
Hao
,
Jiaqi
Lv
,
Peng-Fei
Wang
,
Yu-Han
Zhang
,
Fa-Nian
Shi
,
Yuhan
Wu
Abstract: In this work, Cu1.04Mn0.96O2 nanosheets were synthesized via a simple hydrothermal method, and their electrochemical lithium storage properties and reaction mechanisms were investigated. The nanosheet structure effectively promotes electron transfer and shortens the transport path. Additionally, the partial substitution of Cu for Mn decreases the Jahn-Teller distortion of the MnO6 octahedron. Employing as an anode for Li-ion batteries, the specific capacity reached 610.91 mAh g−1 after 100 cycles at a current density of 100 mA g−1.
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Oct 2024
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