I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[127494]
Abstract: Conventional cathodes for Li-ion batteries are layered transition-metal oxides that support Li+ intercalation charge-balanced by redox on the transition metals. Oxidation beyond one electron per transition metal can be achieved in Li-rich layered oxides by involving structural anions, which necessitates high voltages and complex charge compensation mechanisms convoluted by degradation reactions. We report a detailed structural and spectroscopic analysis of the multielectron material Li2Ru0.3Mn0.7O3, chosen due to its low Ru content. Ex situ and operando spectroscopic data over multiple cycles highlight the changing charge compensation mechanism. Notably, over half of the first-cycle capacity is attributed to O2 gas evolution and reversible O redox is minimal. Instead, reduced Ru and Mn species are detected in the bulk and on the surface, which then increasingly contribute to charge compensation as more metal reduction occurs with cycling. Permanent structural changes linked to metal migration are observed with EXAFS and Raman analysis.
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Dec 2022
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I09-Surface and Interface Structural Analysis
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Nicholas H.
Bashian
,
Mateusz
Zuba
,
Ahamed
Irshad
,
Shona M.
Becwar
,
Julija
Vinckeviciute
,
Warda
Rahim
,
Kent J.
Griffith
,
Eric T.
Mcclure
,
Joseph K.
Papp
,
Bryan D.
Mccloskey
,
David O.
Scanlon
,
Bradley F.
Chmelka
,
Anton
Van Der Ven
,
Sri R.
Narayan
,
Louis F. J.
Piper
,
Brent
Melot
Diamond Proposal Number(s):
[22250]
Abstract: We report on the electrochemical fluorination of the A-site vacant perovskite ReO3 using high-temperature solid-state cells as well as room-temperature liquid electrolytes. Using galvanostatic oxidation and electrochemical impedance spectroscopy, we find that ReO3 can be oxidized by approximately 0.5 equiv of electrons when in contact with fluoride-rich electrolytes. Results from our density functional theory calculations clearly rule out the most intuitive mechanism for charge compensation, whereby F-ions would simply insert onto the A-site of the perovskite structure. Operando X-ray diffraction, neutron total scattering measurements, X-ray spectroscopy, and solid-state 19F NMR with magic-angle spinning were, therefore, used to explore the mechanism by which fluoride ions react with the ReO3 electrode during oxidation. Taken together, our results indicate that a complex structural transformation occurs following fluorination to stabilize the resulting material. While we find that this process of fluorinating ReO3 appears to be only partially reversible, this work demonstrates a practical electrolyte and cell design that can be used to evaluate the mobility of small anions like fluoride that is robust at room temperature and opens new opportunities for exploring the electrochemical fluorination of many new materials.
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Jul 2021
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I09-Surface and Interface Structural Analysis
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Zachary W.
Lebens-Higgins
,
Hyeseung
Chung
,
Israel
Temprano
,
Mateusz
Zuba
,
Jinpeng
Wu
,
Jatinkumar
Rana
,
Carlos
Mejia
,
Michael A.
Jones
,
Le
Wang
,
Clare P.
Grey
,
Yingge
Du
,
Wanli
Yang
,
Ying Shirley
Meng
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[22250, 22148]
Abstract: Interest in alkali‐rich oxide cathodes has grown in an effort to identify systems that provide high energy densities through reversible oxygen redox. However, some of the most promising compositions such as those based solely on earth abundant elements, e. g., iron and manganese, suffer from poor capacity retention and large hysteresis. Here, we use the disordered rocksalt cathode, Li1.3Fe0.4Nb0.3O2, as a model system to identify the underlying origin for the poor performance of Li‐rich iron‐based cathodes. Using elementally specific spectroscopic probes, we find the first charge is primarily accounted for by iron oxidation to 4+ below 4.25 V and O2 gas release beyond 4.25 V with no evidence of bulk oxygen redox. Although the Li1.3Fe0.4Nb0.3O2 is not a viable oxygen redox cathode, the iron 3+/4+ redox couple can be used reversibly during cycling.
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Jan 2021
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Abstract: The importance of metal migration during multi-electron redox activity has been characterized, revealing a competing demand to satisfy bonding requirements and local strains in structures upon alkali intercalation. The local structural evolution required to accommodate intercalation in Y2(MoO4)3 and Al2(MoO4)3 has been contrasted by operando characterization methods, including X-ray absorption spectroscopy and diffraction, along with nuclear magnetic resonance measurements. Computational modeling further rationalized behavioral differences. The local structure of Y2(MoO4)3 was maintained upon lithiation while the structure of Al2(MoO4)3 underwent substantial local atomic rearrangements as the stronger ionic character of the bonds in Al2(MoO4)3 allowed Al to mix off its starting octahedral position to accommodate strain during cycling. However, this mixing was prevented in the more covalent Y2(MoO4)3 which accommodated strain through rotational motion of polyhedral subunits. Knowing that an increased ionic character can facilitate the diffusion of redox-inactive metals when cycling multi-electron electrodes offers a powerful design principle when identifying next-generation intercalation hosts.
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Apr 2020
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I09-Surface and Interface Structural Analysis
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Zachary W.
Lebens-Higgins
,
Hyeseung
Chung
,
Mateusz J.
Zuba
,
Jatinkumar
Rana
,
Yixuan
Li
,
Nicholas V.
Faenza
,
Nathalie
Pereira
,
Bryan D.
Mccloskey
,
Fanny
Rodolakis
,
Wanli
Yang
,
M. Stanley
Whittingham
,
Glenn G.
Amatucci
,
Ying Shirley
Meng
,
Tien-Lin
Lee
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[22250, 22148]
Abstract: Sensitivity to the `bulk' oxygen core orbital makes hard X-ray photoelectron spectroscopy (HAXPES) an appealing technique for studying oxygen redox candidates. Various studies have reported an additional O 1s peak (530-531 eV) at high voltages, which has been considered a direct signature of the bulk oxygen redox process. Here, we find the emergence of a 530.4 eV O 1s HAXPES peak for three model cathodes, Li2MnO3, Li-rich NMC, and NMC 442, that shows no clear link to expected oxygen redox. Instead, the 530.4 eV peak for these three systems is attributed to transition metal reduction and electrolyte decomposition in the near-surface region. Claims of oxygen redox relying on photoelectron spectroscopy must explicitly account for the surface sensitivity of this technique and the extent of the cathode degradation layer.
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Feb 2020
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I09-Surface and Interface Structural Analysis
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Jatinkumar
Rana
,
Joseph K.
Papp
,
Zachary
Lebens-Higgins
,
Mateusz
Zuba
,
Lori A.
Kaufman
,
Anshika
Goel
,
Richard
Schmuch
,
Martin
Winter
,
M. Stanley
Whittingham
,
Wanli
Yang
,
Bryan D.
Mccloskey
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[22250]
Abstract: Though Li2MnO3 was originally considered to be electrochemically inert, its observed activation has spawned a new class of Li-rich layered compounds that deliver capacities beyond the traditional transition-metal redox limit. Despite progress in our understanding of oxygen redox in Li-rich compounds, the underlying origin of the initial charge capacity of Li2MnO3 remains hotly contested. To resolve this issue, we review all possible charge compensation mechanisms including bulk oxygen redox, oxidation of Mn4+, and surface degradation for Li2MnO3 cathodes displaying capacities exceeding 350 mAh g–1. Using elemental and orbital selective X-ray spectroscopy techniques, we rule out oxidation of Mn4+ and bulk oxygen redox during activation of Li2MnO3. Quantitative gas-evolution and titration studies reveal that O2 and CO2 release accounted for a large fraction of the observed capacity during activation with minor contributions from reduced Mn species on the surface. These studies reveal that, although Li2MnO3 is considered critical for promoting bulk anionic redox in Li-rich layered oxides, Li2MnO3 by itself does not exhibit bulk oxygen redox or manganese oxidation beyond its initial Mn4+ valence.
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Jan 2020
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I09-Surface and Interface Structural Analysis
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Sebastian A.
Howard
,
Christopher N.
Singh
,
Galo J.
Paez
,
Matthew
Wahila
,
Linda W.
Wangoh
,
Shawn
Sallis
,
Keith
Tirpak
,
Yufeng
Liang
,
David
Prendergast
,
Mateusz
Zuba
,
Jatinkumar
Rana
,
Alex
Weidenbach
,
Timothy M.
Mccrone
,
Wanli
Yang
,
Tien-Lin
Lee
,
Fanny
Rodolakis
,
William
Doolittle
,
Wei-Cheng
Lee
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[20647]
Open Access
Abstract: The discovery of analog LixNbO2 memristors revealed a promising new memristive mechanism wherein the diffusion of Li+ rather than O2− ions enables precise control of the resistive states. However, directly correlating lithium concentration with changes to the electronic structure in active layers remains a challenge and is required to truly understand the underlying physics. Chemically delithiated single crystals of LiNbO2 present a model system for correlating lithium variation with spectroscopic signatures from operando soft x-ray spectroscopy studies of device active layers. Using electronic structure modeling of the x-ray spectroscopy of LixNbO2 single crystals, we demonstrate that the intrinsic memristive behavior in LixNbO2 active layers results from field-induced degenerate p-type doping. We show that electrical operation of LixNbO2-based memristors is viable even at marginal Li deficiency and that the analog memristive switching occurs well before the system is fully metallic. This study serves as a benchmark for material synthesis and characterization of future LixNbO2-based memristor devices and suggests that valence change switching is a scalable alternative that circumvents the electroforming typically required for filamentary-based memristors.
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Jul 2019
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I09-Surface and Interface Structural Analysis
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Matthew J.
Wahila
,
Galo
Paez
,
Christopher N.
Singh
,
Anna
Regoutz
,
Shawn
Sallis
,
Mateusz J.
Zuba
,
Jatinkumar
Rana
,
M. Brooks
Tellekamp
,
Jos E.
Boschker
,
Toni
Markurt
,
Jack E. N.
Swallow
,
Leanne A. H.
Jones
,
Tim D.
Veal
,
Wanli
Yang
,
Tien-Lin
Lee
,
Fanny
Rodolakis
,
Jerzy T.
Sadowski
,
David
Prendergast
,
Wei-Cheng
Lee
,
W. Alan
Doolittle
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[20647, 21430]
Abstract: The metal-insulator transition of
NbO
2
is thought to be important for the functioning of recent niobium oxide-based memristor devices, and is often described as a Mott transition in these contexts. However, the actual transition mechanism remains unclear, as current devices actually employ electroformed
NbO
x
that may be inherently different to crystalline
NbO
2
. We report on our synchrotron x-ray spectroscopy and density-functional-theory study of crystalline, epitaxial
NbO
2
thin films grown by pulsed laser deposition and molecular beam epitaxy across the metal-insulator transition at
∼
810
∘
C
. The observed spectral changes reveal a second-order Peierls transition driven by a weakening of Nb dimerization without significant electron correlations, further supported by our density-functional-theory modeling. Our findings indicate that employing crystalline
NbO
2
as an active layer in memristor devices may facilitate analog control of the resistivity, whereby Joule-heating can modulate Nb-Nb dimer distance and consequently control the opening of a pseudogap.
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Jul 2019
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I09-Surface and Interface Structural Analysis
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Zachary W.
Lebens-Higgins
,
Nicholas V.
Faenza
,
Maxwell D.
Radin
,
Hao
Liu
,
Shawn
Sallis
,
Jatinkumar
Rana
,
Julija
Vinckeviciute
,
Philip J.
Reeves
,
Mateusz
Zuba
,
Fadwa
Badway
,
Nathalie
Pereira
,
Karena W.
Chapman
,
Tien-Lin
Lee
,
Tianpin
Wu
,
Clare P.
Grey
,
Brent
Melot
,
Anton
Van Der Ven
,
Glenn G.
Amatucci
,
Wanli
Yang
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[19162]
Open Access
Abstract: Oxygen participation, arising from increased transition metal–oxygen covalency during delithiation, is considered essential for the description of charge compensation in conventional layered oxides. The advent of high-resolution mapping of the O K-edge resonant inelastic X-ray scattering (RIXS) provides an opportunity to revisit the onset and extent of oxygen participation. Combining RIXS with an array of structural and electronic probes for the family of Ni-rich LiNi0.8Co0.2−yAlyO2 cathodes, we identify common charge compensation regimes that are assigned to formal transition metal redox (<4.25 V) and oxygen participation through covalency (>4.25 V). From O K-edge RIXS maps, we find the emergence of a sharp RIXS feature in these systems when approaching full delithiation, which has previously been associated with lattice oxidized oxygen in alkali-rich systems. The lack of transition metal redox signatures and strong covalency at these high degrees of delithiation suggest this RIXS feature is similarly attributed to lattice oxygen charge compensation as in the alkali-rich systems. The RIXS feature's evolution with state of charge in conventional layered oxides is evidence that this feature reflects the depopulation of occupied O 2p states associated with oxygen participation.
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Jul 2019
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Nicholas H.
Bashian
,
Shiliang
Zhou
,
Mateusz
Zuba
,
Alex M.
Ganose
,
Joseph W.
Stiles
,
Allyson
Ee
,
David S.
Ashby
,
David O.
Scanlon
,
Louis F. J.
Piper
,
Bruce S.
Dunn
,
Brent C.
Melot
Open Access
Abstract: Understanding the structural transformations that materials undergo during the insertion and deinsertion of Li-ions is crucial for designing high performance intercalation hosts as these deformations can lead to significant capacity fade over time. Here we present a study of the metallic defect perovskite ReO3, with the goal of determining whether these distortions are driven by polaronic charge transport (i.e. the electrons and ions moving through the lattice in a coupled way) due to the semiconducting nature of most oxide hosts. Employing a range of techniques including galvanostatic/potentiometric electrochemical probes, operando X-ray diffraction, X-ray photoelectron spectroscopy, and density functional theory calculations we nd that the cubic structure of ReO3 experiences multiple phase changes involving the correlated twisting of rigid octahedral subunits during the insertion of two equivalents of Li-ions. This extensive rearrangement of the structure results in exceptionally poor long-term cyclability due to large strains that result within the structure, all in spite of the fact that the phase retains its metallic character for all values of Li content from ReO3 to Li2ReO3. These results suggest that phase transformations during alkali ion intercalation are the result of local strains in the lattice and not exclusively due to polaron migration.
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Sep 2018
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