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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E01-JEM ARM 200CF
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Diamond Proposal Number(s):
[32135]
Open Access
Abstract: Understanding Li+ ion diffusion pathways in Li-rich layered transition metal (TM) oxides is crucial for understanding the sluggish kinetics in anionic O2– redox. Although Li diffusion within the alkali layers undergoes a low-barrier octahedral–tetrahedral–octahedral pathway, it is less clear how Li diffuses in and out of the TM layers, particularly given the complex structural rearrangements that take place during the oxidation of O2–. Here, we develop simultaneous electron ptychography and annular dark field imaging methods to unlock the Li migration pathways in Li1.2Ni0.13Mn0.54Co0.13O2 associated with structural changes in the charge–discharge cycle. At the end of TM oxidation and before the high-voltage O oxidation plateau, we show that the Li migrating out of the TM layers occupies the alkali-layer tetrahedral sites on opposite sides of the TM layers, forming Li–Li dumbbell configurations, consistent with the density functional theory calculations. Also occurring are the TM migration and phase transition from O3 to O1 stacking, leading to unstable tetrahedral Li and the absence of Li contrast in imaging. Upon further Li deintercalation to 4.8 V, most of the tetrahedral Li are removed. After discharging to 2 V, we did not identify the reformation of tetrahedral Li but observed permanently migrated TMs at the alkali-layer sites, disfavoring the Li occupying the tetrahedral sites for diffusion. Our findings suggest a landscape of Li diffusion pathways in Li-rich layered oxides and strategies for minimizing the disruption of Li diffusion.
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Aug 2024
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I15-1-X-ray Pair Distribution Function (XPDF)
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Mikkel
Juelsholt
,
Jun
Chen
,
Miguel A.
Pérez-Osorio
,
Gregory
Rees
,
Sofia
De Sousa Coutinho
,
Helen E.
Maynard-Casely
,
Jue
Liu
,
Michelle
Everett
,
Stefano
Agrestini
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Robert A.
House
,
Peter G.
Bruce
Diamond Proposal Number(s):
[27764, 29028]
Open Access
Abstract: LiNiO2 remains a critical archetypal material for high energy density Li-ion batteries, forming the basis of Ni-rich cathodes in use today. Nevertheless, there are still uncertainties surrounding the charging mechanism at high states of charge and the potential role of oxygen redox. We show that oxidation of O2− across the 4.2 V vs. Li+/Li plateau forms O2 trapped in the particles and is accompanied by the formation of 8% Ni vacancies on the transition metal sites of previously fully dense transition metal layers. Such Ni vacancy formation on charging activates O-redox by generating non-bonding O 2p orbitals and is necessary to form vacancy clusters to accommodate O2 in the particles. Ni accumulates at and near the surface of the particles on charging, forming a Ni-rich shell approximately 5 nm thick; enhanced by loss of O2 from the surface, the resulting shell composition is Ni2.3+1.75O2. The overall Ni oxidation state of the particles measured by XAS in fluorescence yield mode after charging across the plateau to 4.3 V vs. Li+/Li is approximately +3.8; however, taking account of the shell thickness and the shell Ni oxidation state of +2.3, this indicates a Ni oxidation state in the core closer to +4 for compositions beyond the plateau.
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Mar 2024
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I22-Small angle scattering & Diffraction
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Brian R.
Pauw
,
Glen J.
Smales
,
Andy
Anker
,
Venkatasamy
Annadurai
,
Daniel M.
Balazs
,
Ralf
Bienert
,
Wim G.
Bouwman
,
Ingo
Breßler
,
Joachim
Breternitz
,
Erik S.
Brok
,
Gary
Bryant
,
Andrew
Clulow
,
Erin R.
Crater
,
Frédéric
De Geuser
,
Alessandra
Del Giudice
,
Jérôme
Deumer
,
Sabrina
Disch
,
Shankar
Dutt
,
Kilian
Frank
,
Emiliano
Fratini
,
Paulo R. A. F.
Garcia
,
Elliot P.
Gilbert
,
Marc B.
Hahn
,
James
Hallett
,
Max
Hohenschutz
,
Martin J.
Hollamby
,
Steven
Huband
,
Jan
Ilavsky
,
Johanna K.
Jochum
,
Mikkel
Juelsholt
,
Bradley W.
Mansel
,
Paavo
Penttilä
,
Rebecca K.
Pittkowski
,
Giuseppe
Portale
,
Lilo D.
Pozzo
,
Leonhard
Rochels
,
Julian M.
Rosalie
,
Patrick E. J.
Saloga
,
Susanne
Seibt
,
Andrew J.
Smith
,
Gregory N.
Smith
,
Glenn A.
Spiering
,
Tomasz M.
Stawski
,
Olivier
Taché
,
Andreas F.
Thünemann
,
Kristof
Toth
,
Andrew E.
Whitten
,
Joachim
Wuttke
Open Access
Abstract: A round-robin study has been carried out to estimate the impact of the human element in small-angle scattering data analysis. Four corrected datasets were provided to participants ready for analysis. All datasets were measured on samples containing spherical scatterers, with two datasets in dilute dispersions and two from powders. Most of the 46 participants correctly identified the number of populations in the dilute dispersions, with half of the population mean entries within 1.5% and half of the population width entries within 40%. Due to the added complexity of the structure factor, far fewer people submitted answers on the powder datasets. For those that did, half of the entries for the means and widths were within 44 and 86%, respectively. This round-robin experiment highlights several causes for the discrepancies, for which solutions are proposed.
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Dec 2023
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I09-Surface and Interface Structural Analysis
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Rose M.
Snyder
,
Mikkel
Juelsholt
,
Curran
Kalha
,
Jason
Holm
,
Elisabeth
Mansfield
,
Tien-Lin
Lee
,
Pardeep K.
Thakur
,
Aysha A.
Riaz
,
Benjamin
Moss
,
Anna
Regoutz
,
Christina S.
Birkel
Diamond Proposal Number(s):
[29451]
Abstract: MAX phases with the general formula Mn+1AXn are layered carbides, nitrides, and carbonitrides with varying stacking sequence of layers of M6X octahedra and the A element depending on n. While “211” MAXphases (n = 1) are very common, MAX phases with higher n, especially n ≥ 3, have hardly been prepared. This work addresses open questions regarding the synthesis conditions, structure, and chemical composition of the “514” MAX phase. In contrast to literature reports, no oxide is needed to form the MAX phase, yet multiple heating steps at 1,600 °C are required. Using high-resolution X-ray diffraction, the structure of (Mo1-xVx)5AlC4 is thoroughly investigated, and Rietveld refinement suggests P-6c2 as the most fitting space group. SEM/EDS and XPS show that the chemical composition of the MAX phase is (Mo0.75V0.25)5AlC4. It was also exfoliated into its MXene sibling (Mo0.75V0.25)5C4 using two different techniques (using HF and an HF/HCl mixture) that lead to different surface terminations as shown by XPS/HAXPES measurements. Initial investigations of the electrocatalytic properties of both MXene versions show that, depending on the etchant, (Mo0.75V0.25)5C4 can reduce hydrogen at 10 mA cm–2 with an overpotential of 166 mV (HF only) or 425 mV (HF/HCl) after cycling the samples, which makes them a potential candidate as an HER catalyst.
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Jun 2023
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I15-1-X-ray Pair Distribution Function (XPDF)
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Jette K.
Mathiesen
,
Espen D.
Bøjesen
,
Jack K.
Pedersen
,
Emil T. S.
Kjær
,
Mikkel
Juelsholt
,
Susan
Cooper
,
Jonathan
Quinson
,
Andy S.
Anker
,
Geoff
Cutts
,
Dean S.
Keeble
,
Maria S.
Thomsen
,
Jan
Rossmeisl
,
Kirsten M. Ø.
Jensen
Diamond Proposal Number(s):
[20187]
Open Access
Abstract: Intermetallic nanoparticles (NPs) have shown enhanced catalytic properties as compared to their disordered alloy counterparts. To advance their use in green energy, it is crucial to understand what controls the formation of intermetallic NPs over alloy structures. By carefully selecting the additives used in NP synthesis, it is here shown that monodisperse, intermetallic PdCu NPs can be synthesized in a controllable manner. Introducing the additives iron(III) chloride and ascorbic acid, both morphological and structural control can be achieved. Combined, these additives provide a synergetic effect resulting in precursor reduction and defect-free growth; ultimately leading to monodisperse, single-crystalline, intermetallic PdCu NPs. Using in situ X-ray total scattering, a hitherto unknown transformation pathway is reported that diverges from the commonly reported coreduction disorder–order transformation. A Cu-rich structure initially forms, which upon the incorporation of Pd(0) and atomic ordering forms intermetallic PdCu NPs. These findings underpin that formation of stoichiometric intermetallic NPs is not limited by standard reduction potential matching and coreduction mechanisms, but is instead driven by changes in the local chemistry. Ultimately, using the local chemistry as a handle to tune the NP structure might open new opportunities to expand the library of intermetallic NPs by exploiting synthesis by design.
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Apr 2022
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B18-Core EXAFS
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Diamond Proposal Number(s):
[20060]
Abstract: Sol–gel chemistry, while being extremely established, is to this day not fully understood, and much of the underlying chemistry and mechanisms are yet to be unraveled. Here, we elaborate on the sol–gel chemistry of Cr2GaC, the first layered ternary carbide belonging to the MAX phase family to ever be synthesized using this wet chemical approach. Leveraging a variety of both in- and ex situ characterization techniques, including X-ray and neutron powder diffraction, X-ray absorption fine structure analyses, total scattering analyses, and differential scanning calorimetry coupled with mass spectrometry, in-depth analyses of the local structures and reaction pathways are elucidated. While the metals first form tetrahedrally and octahedrally coordinated oxidic structures, that subsequently grow and crystallize into oxides, the carbon source citric acid sits on a separate reaction pathway, that does not merge with the metals until the very end. In fact, after decomposing it remains nanostructured and disordered graphite until the temperature allows for the reduction of the metal oxides into the layered carbide. Based on this, we hypothesize that the method is mostly applicable to systems where the needed metals are reducible by graphite around the formation temperature of the target phase.
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Feb 2022
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B18-Core EXAFS
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Gustav W.
Sievers
,
Anders W.
Jensen
,
Jonathan
Quinson
,
Alessandro
Zana
,
Francesco
Bizzotto
,
Mehtap
Oezaslan
,
Alexandra
Dworzak
,
Jacob J. K.
Kirkensgaard
,
Thomas E. L.
Smitshuysen
,
Shima
Kadkhodazadeh
,
Mikkel
Juelsholt
,
Kirsten M. Ø.
Jensen
,
Kirsten
Anklam
,
Hao
Wan
,
Jan
Schäfer
,
Klára
Čépe
,
María
Escudero-Escribano
,
Jan
Rossmeisl
,
Antje
Quade
,
Volker
Brüser
,
Matthias
Arenz
Diamond Proposal Number(s):
[12746]
Abstract: Several concepts for platinum-based catalysts for the oxygen reduction reaction (ORR) are presented that exceed the US Department of Energy targets for Pt-related ORR mass activity. Most concepts achieve their high ORR activity by increasing the Pt specific activity at the expense of a lower electrochemically active surface area (ECSA). In the potential region controlled by kinetics, such a lower ECSA is counterbalanced by the high specific activity. At higher overpotentials, however, which are often applied in real systems, a low ECSA leads to limitations in the reaction rate not by kinetics, but by mass transport. Here we report on self-supported platinum–cobalt oxide networks that combine a high specific activity with a high ECSA. The high ECSA is achieved by a platinum–cobalt oxide bone nanostructure that exhibits unprecedentedly high mass activity for self-supported ORR catalysts. This concept promises a stable fuel-cell operation at high temperature, high current density and low humidification.
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Aug 2020
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