I09-Surface and Interface Structural Analysis
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Galo J.
Paez Fajardo
,
Meltiani
Belekoukia
,
Satish
Bolloju
,
Eleni
Fiamegkou
,
Ashok S.
Menon
,
Zachary
Ruff
,
Zonghao
Shen
,
Nickil
Shah
,
Erik
Bjorklund
,
Mateusz Jan
Zuba
,
Tien-Lin
Lee
,
Pardeep K.
Thakur
,
Robert S.
Weatherup
,
Ainara
Aguadero
,
Melanie J.
Loveridge
,
Clare
Grey
,
Louis F. J.
Piper
Open Access
Abstract: The capacity retention of commercially-sourced pouch cells with single crystal Al surface-doped Ni-rich cathodes (LiNi0.834Mn0.095Co0.071O2) is examined. The degradation-induced capacity fade becomes more pronounced as the upper-cut-off voltage (UCV) increases from 4.2 V to 4.3 V (vs. graphite) at a fixed cycling temperature (either 25 or 40 °C). However, cycles with 4.3 V UCV (slightly below the oxygen loss onset) show better capacity retention upon increasing the cycling temperature from 25 °C to 40 °C. Namely, after 500 cycles at 4.3 V UCV, cycling temperature at 40 °C retains 85.5% of the initial capacity while cycling at 25 °C shows 75.0% capacity retention. By employing a suite of electrochemical, X-ray spectroscopy and secondary ion mass spectrometry techniques, we attribute the temperature-induced improvement of the capacity retention at high UCV to the combined effects of Al surface-dopants, electrochemically resilient single crystal Ni-rich particles, and thermally-improved Li kinetics translating into better electrochemical performance. If cycling remains below the lattice oxygen loss onset, improved capacity retention in industrial cells should be achieved in single crystal Ni-rich cathodes with the appropriate choice of cycling parameter, particle quality, and particle surface dopants.
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Sep 2023
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B18-Core EXAFS
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Open Access
Abstract: Lithium vanadyl phosphate (LiVOPO4) is a next-generation multielectron battery cathode that can intercalate up to two Li-ions per V-ion through the redox couples of V4+/V3+ and V5+/V4+. However, its rate capacity is undermined by the sluggish Li-ion diffusion in the high-voltage region (4 V for V5+/V4+ redox). Nb substitution was used to expand the crystal lattice to facilitate Li-ion diffusion. In this work, Nb substitution was achieved via hydrothermal synthesis, which resulted in a new, lower symmetry β′-LiVOPO4 phase with preferential Nb occupation of one of the two V sites. This phase presents complex defect chemistries, including cation vacancies and hydrogen interstitials, characterized by a combination of X-ray and neutron diffraction, elemental and thermogravimetric analyses, X-ray absorption spectroscopy, and magnetic susceptibility measurements. The Nb-substituted samples demonstrated improved capacity retention and rate capabilities in the high-voltage region, albeit an enlarged voltage hysteresis related to a partial V4+/V3+ redox reaction, as evidenced by ex-situ X-ray absorption spectroscopy and pair distribution function analysis. This work highlights the importance of understanding the complex defect chemistry and its consequence on electrochemistry in polyanionic intercalation compounds.
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Apr 2023
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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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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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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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