I15-1-X-ray Pair Distribution Function (XPDF)
I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[35064, 39285, 40912]
Open Access
Abstract: Li-rich disordered rocksalts are promising next-generation cathode materials for Li-ion batteries. Recent reports have shown it is also possible to obtain Na-rich disordered rocksalts, however, it is currently poorly understood how the knowledge of the structural and redox chemistry translates from the Li-rich to the Na-rich analogs. Here, the properties of Li2MnO2F and Na2MnO2F are compared, which have different ion sizes (Li+ = 0.76 vs Na+ = 1.02 Å) but the same disordered rocksalt structure and stoichiometry. It is found that Na2MnO2F exhibits lower voltage Mn- and O-redox couples, opening access to a wider compositional range within the same voltage limits. Furthermore, the intercalation mechanism switches from predominantly single-phase solid solution behavior in Li2MnO2F to a two-phase transition in Na2MnO2F, accompanied by a greater decrease in the average Mn─O/F bond length. Li2MnO2F retains its long-range disordered rocksalt structure throughout the first cycle. In contrast, Na2MnO2F becomes completely amorphous during charge and develops a local structure characteristic of a post-spinel. This amorphization is partially reversible on discharge. The results show how the ion intercalation behavior of disordered rocksalts differs dramatically when changing from Li- to Na-ions and offers routes to control the electrochemical properties of these high-energy-density cathodes.
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May 2025
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[32023]
Open Access
Abstract: Activation of oxygen anion redox represents an effective method of increasing the specific capacity as well as raising the operating voltage of layered sodium transition metal oxides. However, these reactions are often accompanied by irreversible structural transformations and detrimental side‑reactions between the electrolyte and electrode interface which accelerate degradation, thereby impeding their practical application. To optimise the oxygen anion reversibility for practical use and compare the effects of dopants, we investigated Zn- and Ti-substitution both separately and combined in P3‑structure Na0.7Mn0.75Ni0.25O2, assisted by DFT calculations. The Zn-substituted materials, Na0.7Mn0.65Ni0.25Zn0.1O2 and Na0.7Mn0.58Ni0.25Zn0.07Ti0.1O2 present superior cycling stability over the high voltage range 3.8-4.3 V and enhanced rate capability, delivering a reversible capacity of ~80 mA h g‑1 at 500 mA g‑1 over the voltage window 2.2‑4.3 V compared with 58.6 mA h g-1 for the parent-phase. The improved electrochemical performance of the Zn-substituted materials is attributed to suppression of the P3 to O’3 phase transformation revealed by X‑ray diffraction and the lower electronegativity and filled d ‑band of Zn. The presence of TiO6 octahedra in the Ti-substituted materials relieves structural distortions/TM ordering, also improving the cycling stability. With Zn/Ti co-substitution these advantages may be combined, as demonstrated by the superior electrochemical performance observed for Na0.7Mn0.58Ni0.25Zn0.07Ti0.1O2.
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Jan 2025
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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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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)
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Robert A.
House
,
Yuan
Quan
,
Dingqiao
Ji
,
Yi
Yuan
,
Hang
Xu
,
Rui
Qi
,
Sofia
De Sousa Coutinho
,
Sibylle
Riedel
,
Zhirong
Zhao-Karger
,
Lijiang
Song
,
Alex W
Robertson
,
Peter G.
Bruce
Diamond Proposal Number(s):
[35103]
Open Access
Abstract: The discovery of new transition metal (TM) oxide cathodes which can act as intercalation hosts for Mg2+ ions is critical for the development of high energy density Mg-ion batteries. In Li-ion batteries, disordered rocksalts with sufficiently high Li+ charge carrier ion concentration, i.e. Li:TM >1.1, can support fast Li+ diffusion and therefore deliver high capacities (~300 mAh g-1) and rate performance. Here, we investigate a range of simple Mg-rich disordered rocksalt cathodes, Mg2TMO3 (TM = Mn, Ni, Co), which possess similar charge carrier ion concentrations and similar ratios between ion size and interstitial tetrahedron height to the Li-rich disordered rocksalts. We show that, even with high carbon loadings, elevated cycling temperatures and reduced particle and crystallite size, it is not possible to extract Mg2+, indicating Mg2+ transport through Mg-rich cathodes is far less facile than Li+ in the Li-rich counterparts. Despite this, we demonstrate that Li-rich disordered rocksalts, such as Li2-xMnO2F (x = 1), can act as intercalation hosts for Mg2+, opening possible routes to activating these Mg-rich systems.
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Aug 2024
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B18-Core EXAFS
I21-Resonant Inelastic X-ray Scattering (RIXS)
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John-Joseph
Marie
,
Max
Jenkins
,
Jun
Chen
,
Gregory
Rees
,
Veronica
Celorrio
,
Jaewon
Choi
,
Stefano
Agrestini
,
Mirian
Garcia-Fernandez
,
Ke-Jin
Zhou
,
Robert A.
House
,
Peter G.
Bruce
Diamond Proposal Number(s):
[25785]
Open Access
Abstract: Achieving reversible O-redox through the formation of electron–holes on O could hold the key to a new generation of high energy density Na-ion cathodes. However, to date, it has only been demonstrated in a small handful of cathode materials and none of these materials exploit the dual benefit of high voltage transition metal redox and O-redox, instead relying on Mn3+/4+ capacity close to 2 V vs Na+/Na. Here, a new Na-ion cathode exhibiting electron–holes on O is demonstrated, P2-type Na0.67Li0.1Ni0.3Mn0.6O2, which also utilizes the high voltage Ni3+/4+ redox couple to deliver the highest reported energy density among this class of compound. By employing a low Li content and avoiding honeycomb ordering within the transition metal layer, it is possible to stabilize the hole states, and the high voltage plateau is preserved in Na0.67Li0.1Ni0.3Mn0.6O2 over cycling.
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Jul 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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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Diamond Proposal Number(s):
[25785]
Open Access
Abstract: Oxygen redox cathodes, such as Li1.2Ni0.13Co0.13Mn0.54O2, deliver higher energy densities than those based on transition metal redox alone. However, they commonly exhibit voltage fade, a gradually diminishing discharge voltage on extended cycling. Recent research has shown that, on the first charge, oxidation of O2− ions forms O2 molecules trapped in nano-sized voids within the structure, which can be fully reduced to O2− on the subsequent discharge. Here we show that the loss of O-redox capacity on cycling and therefore voltage fade arises from a combination of a reduction in the reversibility of the O2−/O2 redox process and O2 loss. The closed voids that trap O2 grow on cycling, rendering more of the trapped O2 electrochemically inactive. The size and density of voids leads to cracking of the particles and open voids at the surfaces, releasing O2. Our findings implicate the thermodynamic driving force to form O2 as the root cause of transition metal migration, void formation and consequently voltage fade in Li-rich cathodes.
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Mar 2024
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I12-JEEP: Joint Engineering, Environmental and Processing
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Dominic
Spencer-Jolly
,
Varnika
Agarwal
,
Christopher
Doerrer
,
Bingkun
Hu
,
Shengming
Zhang
,
Dominic L. R.
Melvin
,
Hui
Gao
,
Xiangwen
Gao
,
Paul
Adamson
,
Oxana
Magdysyuk
,
Patrick S.
Grant
,
Robert A.
House
,
Peter G.
Bruce
Diamond Proposal Number(s):
[26082]
Open Access
Abstract: Ag-carbon composite interlayers have been reported to enable Li-free (anodeless) cycling of solid-state batteries. Here, we report structural changes in the Ag-graphite interlayer, showing that on charge, Li intercalates electrochemically into graphite, subsequently reacting chemically with Ag to form Li-Ag alloys. Discharge is not the reverse of charge but rather passes through Li-deficient Li-Ag phases. At higher charging rates, Li intercalation into graphite outpaces the chemical reactions with Ag, delaying the formation of the Li-Ag phases and resulting in more Li metal deposition at the current collector. At and above 2.5 mA·cm−2, Li dendrites are not suppressed. Ag nanoparticles do not suppress dendrites more effectively than does an interlayer of graphite alone. Instead, Ag in the carbon interlayer results in more homogeneous Li and Li-Ag formation on the current collector during charge.
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Feb 2023
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I21-Resonant Inelastic X-ray Scattering (RIXS)
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Robert A.
House
,
Gregory J.
Rees
,
Kit
Mccoll
,
John-Joseph
Marie
,
Mirian
Garcia-Fernandez
,
Abhishek
Nag
,
Ke-Jin
Zhou
,
Simon
Cassidy
,
Benjamin J.
Morgan
,
M.
Saiful Islam
,
Peter G.
Bruce
Diamond Proposal Number(s):
[25589]
Abstract: Oxide ions in transition metal oxide cathodes can store charge at high voltage offering a route towards higher energy density batteries. However, upon charging these cathodes, the oxidized oxide ions condense to form molecular O2 trapped in the material. Consequently, the discharge voltage is much lower than charge, leading to undesirable voltage hysteresis. Here we capture the nature of the electron holes on O2− before O2 formation by exploiting the suppressed transition metal rearrangement in ribbon-ordered Na0.6[Li0.2Mn0.8]O2. We show that the electron holes formed are delocalized across the oxide ions coordinated to two Mn (O–Mn2) arranged in ribbons in the transition metal layers. Furthermore, we track these delocalized hole states as they gradually localize in the structure in the form of trapped molecular O2 over a period of days. Establishing the nature of hole states on oxide ions is important if truly reversible high-voltage O-redox cathodes are to be realized.
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Feb 2023
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