B18-Core EXAFS
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Matthew J. W.
Ogley
,
Ashok S.
Menon
,
Gaurav C.
Pandey
,
Galo J.
Paez Fajardo
,
Beth J.
Johnston
,
Innes
Mcclelland
,
Veronika
Majherova
,
Steven
Huband
,
Debashis
Tripathy
,
Israel
Temprano
,
Stefano
Agrestini
,
Veronica
Celorrio
,
Gabriel E.
Perez
,
Samuel G.
Booth
,
Clare P.
Grey
,
Serena A.
Cussen
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[33292, 33173]
Open Access
Abstract: This study refutes the commonly used ionic-bonding model that demarcates transition metal (TM) and oxygen redox using an archetypal Ni-rich layered oxide cathode, LiNi0.8Mn0.1Co0.1O2. Here, charge compensation during delithiation occurs without formal (ionic) Ni oxidation. Instead, oxygen-dominated states control the redox process, facilitated by strong TM-O hybridization, forming bulk-stable 3d8L and 3d8L2 electronic states, where L is a ligand hole. Bulk O–O dimers are observed with O K-edge resonant inelastic X-ray scattering but, critically, without the long-range TM migration or void formation observed in Li-rich layered oxides. Above 4.34 V vs. Li+/Li, the cathode loses O, forming a resistive surface rock-salt layer that causes capacity fade. This highlights the importance of cathode engineering when attempting to achieve higher energy densities with layered oxide cathodes, especially in those where O dominates the charge compensation mechanism.
|
Oct 2024
|
|
B18-Core EXAFS
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Matthew
Ogley
,
Ashok S.
Menon
,
Beth J.
Johnston
,
Gaurav
Pandey
,
Innes
Mcclelland
,
Xiaoqun
Shi
,
Stefano
Agrestini
,
Veronica
Celorrio
,
Gabriel E.
Perez
,
Samuel G.
Booth
,
Jordi
Cabana
,
Serena A.
Cussen
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[33292, 33173]
Open Access
Abstract: In layered lithium transition metal oxide cathodes, high-voltage operation is accompanied by the formation of oxygen dimers, which are widely used as an indicator of oxygen-redox activity. However, understanding the role that oxygen dimerization plays in facilitating charge compensation is still needed. Li2NiO3 (a 3d8L2-containing compound, where L is a ligand hole) is studied as a model system, where oxygen dimerization is shown to occur without cathode oxidation. Electrochemical cycling results in a net reduction of the cathode, accompanied by structural transformations, despite spectroscopic features of oxygen dimers arising at the top-of-charge. Here, oxygen dimerization is shown to coexist alongside a structurally transformed and electronically reduced cathode structure, thus highlighting that O dimerization is independent of bulk redox processes. This makes it clear that a thermodynamically derived transformation toward a reduced phase remains the only variable capable of generating O–O dimers in Li2NiO3.
|
Aug 2024
|
|
I09-Surface and Interface Structural Analysis
|
Galo J.
Paez Fajardo
,
Eleni
Fiamegkou
,
James A.
Gott
,
Heng
Wang
,
Israel
Temprano
,
Ieuan D.
Seymour
,
Matthew J. W.
Ogley
,
Ashok S.
Menon
,
Ifan E. L.
Stephens
,
Muhammad
Ans
,
Tien-Lin
Lee
,
Pardeep K.
Thakur
,
Wesley M.
Dose
,
Michaël F. L.
De Volder
,
Clare P.
Grey
,
Louis F. J.
Piper
Diamond Proposal Number(s):
[30201]
Open Access
Abstract: Oxygen loss at high voltages in Ni-rich NMC//graphite Li-ion batteries promotes degradation, but increasing evidence from full cells reveals that the depth of discharge choice can further accelerate aging, i.e., synergistic degradation. In this Letter, we employ cycling protocols to examine the origin of the synergistic degradation for single crystal Ni-rich NMC//graphite pouch cells. In regimes where oxygen loss is not promoted (V < 4.3 V), a lower cutoff voltage does not affect capacity retention (after 100 cycles), despite significant graphite expansion occurring. In contrast, when NMC surface oxygen loss is induced (V > 4.3 V), deeper depth of discharge leads to pronounced faster aging. Using a combination of post-mortem analysis and density functional theory, we present a mechanistic description of surface phase densification and evolution as a function of voltage and cycling. The detrimental impact of this mechanism on lithium-ion kinetics is used to explain the observed cycling results.
|
Nov 2023
|
|
B18-Core EXAFS
I11-High Resolution Powder Diffraction
|
Diamond Proposal Number(s):
[25166, 14239]
Open Access
Abstract: A Mn2+-Li-Nb disordered rock-salt oxide cathode is prepared by a solid-state reaction under 5% H2/N2, and its electrochemical property shows a high voltage plateau at 4.8 V, with irreversible structural changes in the first cycle due to O redox processes; this is supported by powder X-ray diffraction and ex-situ laboratory Mn K-edge XANES data.
|
Oct 2023
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Sep 2023
|
|
I09-Surface and Interface Structural Analysis
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
A. S.
Menon
,
B. J.
Johnston
,
S. G.
Booth
,
L.
Zhang
,
K.
Kress
,
B. E.
Murdock
,
G.
Paez Fajardo
,
N. N.
Anthonisamy
,
N.
Tapia-Ruiz
,
S.
Agrestini
,
M.
Garcia-Fernandez
,
K.
Zhou
,
P. K.
Thakur
,
T. L.
Lee
,
A. J.
Nedoma
,
S. A.
Cussen
,
L. F. J.
Piper
Diamond Proposal Number(s):
[29104, 29113]
Open Access
Abstract: The desire to increase the energy density of stoichiometric layered
Li
TM
O
2
(TM = 3d transition metal) cathode materials has promoted investigation into their properties at high states of charge. Although there is increasing evidence for pronounced oxygen participation in the charge compensation mechanism, questions remain whether this is true
O
-redox, as observed in
Li
-excess cathodes. Through a high-resolution
O
K-edge resonant inelastic x-ray spectroscopy (RIXS) study of the
Mn
-free
Ni
-rich layered oxide
Li
Ni
0.98
W
0.02
O
2
, we demonstrate that the same oxidized oxygen environment exists in both
Li
-excess and non-
Li
-excess systems. The observation of identical RIXS loss features in both classes of compounds is remarkable given the differences in their crystallographic structure and delithiation pathways. This lack of a specific structural motif reveals the importance of electron correlation in the charge compensation mechanism for these systems and indicates how a better description of charge compensation in layered oxides is required to understand anionic redox for energy storage.
|
Mar 2023
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Dec 2022
|
|
I09-Surface and Interface Structural Analysis
|
Le
Wang
,
Zhenzhong
Yang
,
Widitha S.
Samarakoon
,
Yadong
Zhou
,
Mark E.
Bowden
,
Hua
Zhou
,
Jinhui
Tao
,
Zihua
Zhu
,
Nabajit
Lahiri
,
Timothy C.
Droubay
,
Zachary W.
Lebens-Higgins
,
Xinmao
Yin
,
Chi Sin
Tang
,
Zhenxing
Feng
,
Louis F. J.
Piper
,
Andrew T. S.
Wee
,
Scott A.
Chambers
,
Yingge
Du
Diamond Proposal Number(s):
[19162]
Abstract: Epitaxial growth is a powerful tool for synthesizing heterostructures and integrating multiple functionalities. However, interfacial mixing can readily occur and significantly modify the properties of layered structures, particularly for those containing energy storage materials with smaller cations. Here, we show a two-step sequence involving the growth of an epitaxial LiCoO2 cathode layer followed by the deposition of a binary transition metal oxide. Orientation-controlled epitaxial synthesis of the model solid-state-electrolyte Li2WO4 and anode material Li4Ti5O12 occurs as WO3 and TiO2 nucleate and react with Li ions from the underlying cathode. We demonstrate that this lithiation-assisted epitaxy approach can be used for energy materials discovery and exploring different combinations of epitaxial interfaces that can serve as well-defined model systems for mechanistic studies of energy storage and conversion processes.
|
Jun 2022
|
|
I09-Surface and Interface Structural Analysis
|
Diamond Proposal Number(s):
[25355, 13812]
Abstract: Recent progress in the growth and characterization of thin-film
VO
2
has shown its electronic properties can be significantly modulated by epitaxial matching. To throw new light on the concept of “Mott engineering,” we develop a symmetry-consistent approach to treat structural distortions and electronic correlations in epitaxial
VO
2
films under strain, and compare our design with direct experimental probes. We find strong evidence for the emergence of correlation-driven charge order deep in the metallic phase, and our results indicate that exotic phases of
VO
2
can be controlled with epitaxial stabilization.
|
Jan 2022
|
|
I09-Surface and Interface Structural Analysis
|
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.
|
Jul 2021
|
|
