E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
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Tiarnan A. S.
Doherty
,
Dominik
Kubicki
,
Stuart
Macpherson
,
Young-Kwang
Jung
,
Duncan
Johnstone
,
Affan
Iqbal
,
Dengyang
Guo
,
Kyle
Frohna
,
Mohsen
Danaie
,
Elizabeth
Tennyson
,
Satyawan
Nagane
,
Anna
Abfalterer
,
Miguel
Anaya
,
Yu-Hsien
Chiang
,
Phillip
Crout
,
Francesco Simone
Ruggeri
,
Sean
Collins
,
Clare
Grey
,
Aron
Walsh
,
Paul
Midgley
,
Samuel
Stranks
Diamond Proposal Number(s):
[20420, 24111]
Abstract: There is currently substantial interest in stabilizing the simple ternary FAPbI3 perovskite because of its near-optimal band gap and superior thermal stability compared to methylammonium-based materials.1 The key challenge of FAPbI3 is the thermodynamic instability of the polymorph required for efficient light harvesting. Without additives, the black photoactive α-polymorph is only stable above ca. 160°C. At room temperature, it is metastable and rapidly transitions to the non-perovskite yellow polymorph. The stabilization of the black polymorph at room temperature can be achieved, for example, by adding a small amount of the pernicious MA through use of methylammonium chloride (in conjunction with formamidinium formate),2 methylammonium thiocyanate,3 or methylammonium formate.4 We have developed a new stabilization strategy which does not involve the addition of MA.5 Instead, it uses a surface-templating agent (EDTA) which modifies the material without incorporating into the structure. We use a combination of scanning electron diffraction (SED) and nuclear magnetic resonance spectroscopies (NMR, NQR) to identify the atomic-level mechanism of action of EDTA in this role. We find that it templates the structure by inducing a small octahedral tilt, only resolvable with local characterization techniques, and imparts remarkable phase stability by arresting transitions to low-dimensional polymorphs. This octahedral tilt engineering strategy is remarkably universal, and we show that it is the intrinsic stabilization mechanism in the state-of-the-art FA-rich mixed-cation materials.
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Feb 2022
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[21995, 26285]
Abstract: Ni-rich lithium nickel manganese cobalt (NMC) oxide cathode materials promise Li-ion batteries with increased energy density and lower cost. However, higher Ni content is accompanied by accelerated degradation and thus poor cycle lifetime, with the underlying mechanisms and their relative contributions still poorly understood. Here, we combine electrochemical analysis with surface-sensitive X-ray photoelectron and absorption spectroscopies to observe the interfacial degradation occurring in LiNi0.8Mn0.1Co0.1O2–graphite full cells over hundreds of cycles between fixed cell voltages (2.5–4.2 V). Capacity losses during the first ∼200 cycles are primarily attributable to a loss of active lithium through electrolyte reduction on the graphite anode, seen as thickening of the solid-electrolyte interphase (SEI). As a result, the cathode reaches ever-higher potentials at the end of charge, and with further cycling, a regime is entered where losses in accessible NMC capacity begin to limit cycle life. This is accompanied by accelerated transition-metal reduction at the NMC surface, thickening of the cathode electrolyte interphase, decomposition of residual lithium carbonate, and increased cell impedance. Transition-metal dissolution is also detected through increased incorporation into and thickening of the SEI, with Mn found to be initially most prevalent, while the proportion of Ni increases with cycling. The observed evolution of anode and cathode surface layers improves our understanding of the interconnected nature of the degradation occurring at each electrode and the impact on capacity retention, informing efforts to achieve a longer cycle lifetime in Ni-rich NMCs.
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Feb 2022
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I11-High Resolution Powder Diffraction
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Andrew Stephen
Leach
,
Alice
Llewellyn
,
Chao
Xu
,
Chun
Tan
,
Thomas M. M.
Heenan
,
Alex
Dimitrijevic
,
Karin
Kleiner
,
Clare P.
Grey
,
Dan J. L.
Brett
,
Chiu C.
Tang
,
Paul R.
Shearing
,
Rhodri
Jervis
Diamond Proposal Number(s):
[22498, 24122]
Open Access
Abstract: Understanding the performance of commercially relevant cathode materials for lithium-ion (Li-ion) batteries is vital to realize the potential of high-capacity materials for automotive applications. Of particular interest is the spatial variation of crystallographic behavior across (what can be) highly inhomogeneous electrodes. In this work, a high-resolution X-ray diffraction technique was used to obtain operando transmission measurements of Li-ion pouch cells to measure the spatial variances in the cell during electrochemical cycling. Through spatially resolved investigations of the crystallographic structures, the distribution of states of charge has been elucidated. A larger portion of the charging is accounted for by the central parts, with the edges and corners delithiating to a lesser extent for a given average electrode voltage. The cells were cycled to different upper cutoff voltages (4.2 and 4.3 V vs. graphite) and C-rates (0.5, 1, and 3C) to study the effect on the structure of the NMC811 cathode. By combining this rapid data collection method with a detailed Rietveld refinement of degraded NMC811, the spatial dependence of the degradation caused by long-term cycling (900 cycles) has also been shown. The variance shown in the pristine measurements is exaggerated in the aged cells with the edges and corners offering an even lower percentage of the charge. Measurements collected at the very edge of the cell have also highlighted the importance of electrode alignment, with a misalignment of less than 0.5 mm leading to significantly reduced electrochemical activity in that area.
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Jan 2022
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E02-JEM ARM 300CF
I14-Hard X-ray Nanoprobe
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Tiarnan A. S.
Doherty
,
Satyawan
Nagane
,
Dominik J.
Kubicki
,
Young-Kwang
Jung
,
Duncan N.
Johnstone
,
Affan N.
Iqbal
,
Dengyang
Guo
,
Kyle
Frohna
,
Mohsen
Danaie
,
Elizabeth M.
Tennyson
,
Stuart
Macpherson
,
Anna
Abfalterer
,
Miguel
Anaya
,
Yu-Hsien
Chiang
,
Phillip
Crout
,
Francesco Simone
Ruggeri
,
Sean M.
Collins
,
Clare P.
Grey
,
Aron
Walsh
,
Paul A.
Midgley
,
Samuel D.
Stranks
Diamond Proposal Number(s):
[20420, 24111]
Abstract: Efforts to stabilize photoactive formamidinium (FA)–based halide perovskites for perovskite photovoltaics have focused on the growth of cubic formamidinium lead iodide (α-FAPbI3) phases by empirically alloying with cesium, methylammonium (MA) cations, or both. We show that such stabilized FA-rich perovskites are noncubic and exhibit ~2° octahedral tilting at room temperature. This tilting, resolvable only with the use of local nanostructure characterization techniques, imparts phase stability by frustrating transitions from photoactive to hexagonal phases. Although the bulk phase appears stable when examined macroscopically, heterogeneous cation distributions allow microscopically unstable regions to form; we found that these transitioned to hexagonal polytypes, leading to local trap-assisted performance losses and photoinstabilities. Using surface-bound ethylenediaminetetraacetic acid, we engineered an octahedral tilt into pure α-FAPbI3 thin films without any cation alloying. The templated photoactive FAPbI3 film was extremely stable against thermal, environmental, and light stressors.
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Dec 2021
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I11-High Resolution Powder Diffraction
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Eun Jeong
Kim
,
Philip A.
Maughan
,
Euan N.
Bassey
,
Raphaële J.
Clément
,
Le Anh
Ma
,
Laurent C.
Duda
,
Divya
Sehrawat
,
Reza
Younesi
,
Neeraj
Sharma
,
Clare P.
Grey
,
Robert
Armstrong
Diamond Proposal Number(s):
[26699]
Open Access
Abstract: Activation of oxygen redox represents a promising strategy to enhance the energy density of positive electrode materials in both lithium and sodium-ion batteries. However, the large voltage hysteresis associated with oxidation of oxygen anions during the first charge represents a significant challenge. Here, P3-type Na0.67Li0.2Mn0.8O2 is reinvestigated and a ribbon superlattice is identified for the first time in P3-type materials. The ribbon superstructure is maintained over cycling with very minor unit cell volume changes in the bulk while Li ions migrate reversibly between the transition metal and Na layers at the atomic scale. In addition, a range of spectroscopic techniques reveal that a strongly hybridized Mn 3d–O 2p favors ligand-to-metal charge transfer, also described as a reductive coupling mechanism, to stabilize reversible oxygen redox. By preparing materials under three different synthetic conditions, the degree of ordering between Li and Mn is varied. The sample with the maximum cation ordering delivers the largest capacity regardless of the voltage windows applied. These findings highlight the importance of cationic ordering in the transition metal layers, which can be tuned by synthetic control to enhance anionic redox and hence energy density in rechargeable batteries.
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Dec 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
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Diamond Proposal Number(s):
[18630]
Open Access
Abstract: The structures of Zr and Hf metal–organic frameworks (MOFs) are very sensitive to small changes in synthetic conditions. One key difference affecting the structure of UiO MOF phases is the shape and nuclearity of Zr or Hf metal clusters acting as nodes in the framework; although these clusters are crucial, their evolution during MOF synthesis is not fully understood. In this paper, we explore the nature of Hf metal clusters that form in different reaction solutions, including in a mixture of DMF, formic acid, and water. We show that the choice of solvent and reaction temperature in UiO MOF syntheses determines the cluster identity and hence the MOF structure. Using in situ X-ray pair distribution function measurements, we demonstrate that the evolution of different Hf cluster species can be tracked during UiO MOF synthesis, from solution stages to the full crystalline framework, and use our understanding to propose a formation mechanism for the hcp UiO-66(Hf) MOF, in which first the metal clusters aggregate from the M6 cluster (as in fcu UiO-66) to the hcp-characteristic M12 double cluster and, following this, the crystalline hcp framework forms. These insights pave the way toward rationally designing syntheses of as-yet unknown MOF structures, via tuning the synthesis conditions to select different cluster species.
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Nov 2021
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Chantalle J.
Krajewska
,
Seán R.
Kavanagh
,
Lina
Zhang
,
Dominik J.
Kubicki
,
Krishanu
Dey
,
Krzysztof
Galkowski
,
Clare P.
Grey
,
Samuel D.
Stranks
,
Aron
Walsh
,
David O.
Scanlon
,
Robert G.
Palgrave
Open Access
Abstract: Lead-free halides with perovskite-related structures, such as the vacancy-ordered perovskite Cs3Bi2Br9, are of interest for photovoltaic and optoelectronic applications. We find that addition of SnBr2 to the solution-phase synthesis of Cs3Bi2Br9 leads to substitution of up to 7% of the Bi(III) ions by equal quantities of Sn(II) and Sn(IV). The nature of the substitutional defects was studied by X-ray diffraction, 133Cs and 119Sn solid state NMR, X-ray photoelectron spectroscopy and density functional theory calculations. The resulting mixed-valence compounds show intense visible and near infrared absorption due to intervalence charge transfer, as well as electronic transitions to and from localised Sn-based states within the band gap. Sn(II) and Sn(IV) defects preferentially occupy neighbouring B-cation sites, forming a double-substitution complex. Unusually for a Sn(II) compound, the material shows minimal changes in optical and structural properties after 12 months storage in air. Our calculations suggest the stabilisation of Sn(II) within the double substitution complex contributes to this unusual stability. These results expand upon research on inorganic mixed-valent halides to a new, layered structure, and offer insights into the tuning, doping mechanisms, and structure–property relationships of lead-free vacancy-ordered perovskite structures.
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Nov 2021
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I15-1-X-ray Pair Distribution Function (XPDF)
I15-Extreme Conditions
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Diamond Proposal Number(s):
[17785, 13681]
Abstract: Hard carbons are the leading candidate anode materials for sodium-ion batteries. However, the sodium-insertion mechanisms remain under debate. Here, employing a novel analysis of operando and ex situ pair distribution function (PDF) analysis of total scattering data, supplemented by information on the local electronic structure provided by operando 23Na solid-state NMR, we identify the local atomic environments of sodium stored within hard carbon and provide a revised mechanism for sodium storage. The local structure of carbons is well-described by bilayers of curved graphene fragments, with fragment size increasing, and curvature decreasing with increasing pyrolysis temperature. A correlation is observed between the higher-voltage (slope) capacity and the defect concentration inferred from the size and curvature of the fragments. Meanwhile, a larger lower-voltage (plateau) capacity is observed in samples modeled by larger fragment sizes. Operando PDF data on two commercially relevant hard carbons reveal changes at higher-voltages consistent with sodium ions stored close to defective areas of the carbon, with electrons localized in the antibonding π*-orbitals of the carbon. Metallic sodium clusters approximately 13–15 Å in diameter are formed in both carbons at lower voltages, implying that, for these carbons, the lower-voltage capacity is determined by the number of regions suitable for sodium cluster formation, rather than by having microstructures that allow larger clusters to form. Our results reveal that local atomic structure has a definitive role in determining storage capacity, and therefore the effect of synthetic conditions on both the local atomic structure and the microstructure should be considered when engineering hard carbons.
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Aug 2021
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Nuria
Tapia-Ruiz
,
A. Robert
Armstrong
,
Hande
Alptekin
,
Marco A.
Amores
,
Heather
Au
,
Jerry
Barker
,
Rebecca
Boston
,
William R
Brant
,
Jake M.
Brittain
,
Yue
Chen
,
Manish
Chhowalla
,
Yong-Seok
Choi
,
Sara I. R.
Costa
,
Maria
Crespo Ribadeneyra
,
Serena A
Cussen
,
Edmund J.
Cussen
,
William I. F.
David
,
Aamod V
Desai
,
Stewart A. M.
Dickson
,
Emmanuel I.
Eweka
,
Juan D.
Forero-Saboya
,
Clare
Grey
,
John M.
Griffin
,
Peter
Gross
,
Xiao
Hua
,
John T. S.
Irvine
,
Patrik
Johansson
,
Martin O.
Jones
,
Martin
Karlsmo
,
Emma
Kendrick
,
Eunjeong
Kim
,
Oleg V
Kolosov
,
Zhuangnan
Li
,
Stijn F L
Mertens
,
Ronnie
Mogensen
,
Laure
Monconduit
,
Russell E
Morris
,
Andrew J.
Naylor
,
Shahin
Nikman
,
Christopher A
O’keefe
,
Darren M. C.
Ould
,
Robert G.
Palgrave
,
Philippe
Poizot
,
Alexandre
Ponrouch
,
Stéven
Renault
,
Emily M.
Reynolds
,
Ashish
Rudola
,
Ruth
Sayers
,
David O.
Scanlon
,
S.
Sen
,
Valerie R.
Seymour
,
Begoña
Silván
,
Moulay Tahar
Sougrati
,
Lorenzo
Stievano
,
Grant S.
Stone
,
Chris I.
Thomas
,
Maria-Magdalena
Titirici
,
Jincheng
Tong
,
Thomas J.
Wood
,
Dominic S
Wright
,
Reza
Younesi
Open Access
Abstract: Increasing concerns regarding the sustainability of lithium sources, due to their limited availability and consequent expected price increase, have raised awareness of the importance of developing alternative energy-storage candidates that can sustain the ever-growing energy demand. Furthermore, limitations on the availability of the transition metals used in the manufacturing of cathode materials, together with questionable mining practices, are driving development towards more sustainable elements. Given the uniformly high abundance and cost-effectiveness of sodium, as well as its very suitable redox potential (close to that of lithium), sodium-ion battery technology offers tremendous potential to be a counterpart to lithium-ion batteries (LIBs) in different application scenarios, such as stationary energy storage and low-cost vehicles. This potential is reflected by the major investments that are being made by industry in a wide variety of markets and in diverse material combinations. Despite the associated advantages of being a drop-in replacement for LIBs, there are remarkable differences in the physicochemical properties between sodium and lithium that give rise to different behaviours, for example, different coordination preferences in compounds, desolvation energies, or solubility of the solid–electrolyte interphase inorganic salt components. This demands a more detailed study of the underlying physical and chemical processes occurring in sodium-ion batteries and allows great scope for groundbreaking advances in the field, from lab-scale to scale-up. This roadmap provides an extensive review by experts in academia and industry of the current state of the art in 2021 and the different research directions and strategies currently underway to improve the performance of sodium-ion batteries. The aim is to provide an opinion with respect to the current challenges and opportunities, from the fundamental properties to the practical applications of this technology.
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Jul 2021
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B18-Core EXAFS
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Diamond Proposal Number(s):
[24303]
Open Access
Abstract: P2-layered sodium-ion battery (NIB) cathodes are a promising class of Na-ion electrode materials with high Na+ mobility and relatively high capacities. In this work, we report the structural changes that take place in P2–Na0.67[Mg0.28Mn0.72]O2. Using ex situ X-ray diffraction, Mn K-edge extended X-ray absorption fine structure, and 23Na NMR spectroscopy, we identify the bulk phase changes along the first electrochemical charge–discharge cycle—including the formation of a high-voltage “Z phase”, an intergrowth of the OP4 and O2 phases. Our ab initio transition state searches reveal that reversible Mg2+ migration in the Z phase is both kinetically and thermodynamically favorable at high voltages. We propose that Mg2+ migration is a significant contributor to the observed voltage hysteresis in Na0.67[Mg0.28Mn0.72]O2 and identify qualitative changes in the Na+ ion mobility.
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Jun 2021
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