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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I07-Surface & interface diffraction
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Matteo
Degani
,
Riccardo
Pallotta
,
Giovanni
Pica
,
Masoud
Karimipour
,
Alessandro
Mirabelli
,
Kyle
Frohna
,
Miguel
Anaya
,
Tianyu
Xu
,
Chang-Qi
Ma
,
Samuel D.
Stranks
,
Monica Lira
Cantù
,
Giulia
Grancini
Diamond Proposal Number(s):
[32266]
Open Access
Abstract: Interface engineering using self-assembled 2D perovskite interfaces is a consolidated route to efficient and durable perovskite solar cells. Whether the 2D perovskite forms a homogeneous conformal layer or is heterogeneously distributed on the surface, interface defects are passivated, leading to a general improvement in the device's open circuit voltage (VOC) and stability. Here, an innovative strategy is developed for manipulating the composition of the 2D/3D perovskite interface that results in the formation of a gradient halide distribution, which extends from the surface to the bulk. The use of a bromide-based 2D perovskite triggers a progressive Br/I exchange, affecting not only the surface but also the perovskite underneath. As a result, not only the device VOC improve, as expected, but also the photogenerated current is boosted, leading to a device efficiency of up to 24.4%. Such mixed halide gradient effectively passivates surface and bulk defects making the perovskite active layer more efficient and robust, as demonstrated by the superior device stability showing zero losses in performances upon 36 days (more than 800 h) test in outdoor conditions, those ones relevant for a marketable product.
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Dec 2024
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I09-Surface and Interface Structural Analysis
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Zhilin
Liang
,
Abdulaziz
Baubaid
,
Mariusz
Radtke
,
Maximilian
Mellin
,
Clément
Maheu
,
Sandipan
Maiti
,
Hadar
Sclar
,
Igor
Píš
,
Silvia
Nappini
,
Elena
Magnano
,
Federica
Bondino
,
Robert
Winkler
,
René
Hausbrand
,
Christian
Hess
,
Lambert
Alff
,
Boris
Markovsky
,
Doron
Aurbach
,
Wolfram
Jaegermann
,
Gennady
Cherkashinin
Diamond Proposal Number(s):
[31579]
Open Access
Abstract: The design of cathode/electrolyte interfaces in high-energy density Li-ion batteries is critical to protect the surface against undesirable oxygen release from the cathodes when batteries are charged to high voltage. However, the involvement of the engineered interface in the cationic and anionic redox reactions associated with (de-)lithiation is often ignored, mostly due to the difficulty to separate these processes from chemical/catalytic reactions at the cathode/electrolyte interface. Here, a new electron energy band diagrams concept is developed that includes the examination of the electrochemical- and ionization- potentials evolution upon batteries cycling. The approach enables to forecast the intrinsic stability of the cathodes and discriminate the reaction pathways associated with interfacial electronic charge-transfer mechanisms. Specifically, light is shed on the evolution of cationic and anionic redox in high-energy density lithium-rich 0.33Li2MnO3·0.67LiNi0.4Co0.2Mn0.4O2 (HE-NCM) cathodes, particularly those that undergo surface modification through SO2 and NH3 double-gas treatment to suppress the structural degradation. The chemical composition and energy distribution of the occupied and unoccupied electronic states at the different charging/discharging states are quantitatively estimated by using advanced spectroscopy techniques, including operando Raman spectroscopy. The concept is successfully demonstrated in designing artificial interfaces for high-voltage olivine structure cathodes enabling stable battery operation up to 5.1 V versus Li+/Li.
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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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I09-Surface and Interface Structural Analysis
I15-1-X-ray Pair Distribution Function (XPDF)
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Liquan
Pi
,
Erik
Bjorklund
,
Gregory J.
Rees
,
Weixin
Song
,
Chen
Gong
,
John-Joseph
Marie
,
Xiangwen
Gao
,
Shengda D.
Pu
,
Mikkel
Juelsholt
,
Philip A.
Chater
,
Joohyuk
Park
,
Min Gyu
Kim
,
Jaewon
Choi
,
Stefano
Agrestini
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Alex W.
Robertson
,
Robert S.
Weatherup
,
Robert A.
House
,
Peter G.
Bruce
Diamond Proposal Number(s):
[27336, 29028, 25807]
Abstract: Disordered rocksalt cathodes deliver high energy densities, but they suffer from pronounced capacity and voltage fade on cycling. Here, we investigate fade using two disordered rocksalt lithium manganese oxyfluorides: Li3Mn2O3F2 (Li1.2Mn0.8O1.2F0.8), which stores charge by Mn2+/Mn4+ redox, and Li2MnO2F, where charge storage involves both Mn3+/Mn4+ and oxygen redox (O-redox). Li3Mn2O3F2 is reported for the first time. We identify the growth of an electronically resistive surface layer with cycling that is present in both Li2MnO2F and Li3Mn2O3F2 but more pronounced in the presence of O-redox. This resistive surface inhibits electronic contact between particles, leading to the observed voltage polarization and capacity loss. By increasing carbon loading in the composite cathode, it is possible to substantially improve the cycling performance. These results help to disentangle O-redox from other leading causes of capacity fading in Mn oxyfluorides and highlight the importance of maintaining electronic conductivity in improving capacity and voltage retention.
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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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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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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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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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