Reversible and Irreversible Redox Processes in Li-Rich Layered Oxides

Merz, Michael; Ying, Bixian; Nagel, Peter; Schuppler, S.; Kleiner, Karin

doi:10.1021/acs.chemmater.1c02573

Cited by 21 publications

(18 citation statements)

References 54 publications

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“…During charging, charge compensation is mainly provided by the oxidation of Ni and Co below ≈4.4 V, and the oxidation of lattice oxygen ions above ≈4.4 V; during the discharging process, the oxidized TM ions and lattice oxygen ions are then reduced to balance the charge change induced by the Li reinsertion. [35] The proposed charge compensation processes are consistent with the in situ X-ray diffraction (XRD) results of the LR-NMC sample (Figure 1c). The obvious shrink of the ab-plane at the beginning of the charging process is closely associated with the oxidization of TM ions and the ionic radius reduction (Figure 1d).…”

Section: Resultssupporting

confidence: 83%

Quantifying the Anomalous Local and Nanostructure Evolutions Induced by Lattice Oxygen Redox in Lithium‐Rich Cathodes

Zhao

Zhang

et al. 2022

Small Methods

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Due to their accessible lattice oxygen redox (l‐OR) at high voltages, Li‐rich layered transition metal (TM) oxides have shown promising potential as candidate cathodes for high‐energy‐density Li‐ion batteries. However, this l‐OR process is also associated with unusual electrochemical issues such as voltage hysteresis and long‐term voltage decay. The structure response mechanism to the l‐OR behavior also remains unclear, hindering rational structure optimizations that would enable practical Li‐rich cathodes. Here, this study reveals a strong coupling between l‐OR and structure dynamic evolutions, as well as their effects on the electrochemical properties. Using the technique of neutron total scattering with pair distribution function analysis and small‐angle neutron scattering, this study quantifies the local TM migration and formation of nanopores that accompany the l‐OR. These experiments demonstrate the causal relationships among l‐OR, the local/nanostructure evolutions, and the unusual electrochemistry. The TM migration triggered by the l‐OR can change local oxygen coordination environments, which results in voltage hysteresis. Coupled with formed oxygen vacancies, it will accelerate the formation of nanopores, inducing a phase transition, and leading to irreversible capacity and long‐cycling voltage fade.

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Section: Resultssupporting

confidence: 83%

Quantifying the Anomalous Local and Nanostructure Evolutions Induced by Lattice Oxygen Redox in Lithium‐Rich Cathodes

Zhao

Zhang

et al. 2022

Small Methods

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“…In addition to the processes discussed above, 1 , 22 − 25 this work shows that the Ni oxidation from Ni 2+ to Ni 3+ determines the final performance of the materials. 26 − 28 An incomplete oxidation leads to a poor rate and cycling stability, and the preannealing step is a key factor to ensure proper oxidation. In situ synchrotron and laboratory-based X-ray powder diffraction (SXPD and LXPD) coupled with mass spectrometry (MS) as well as near-edge X-ray absorption spectroscopy (NEXAFS) is used to study the evolution of the layered structures, the oxidation of the transition metals, and water loss upon calcination of Ni-poor (NCM111) and Ni-rich (NCM811) layered oxides.…”

Section: Introductionmentioning

confidence: 99%

Monitoring the Formation of Nickel-Poor and Nickel-Rich Oxide Cathode Materials for Lithium-Ion Batteries with Synchrotron Radiation

et al. 2023

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The syntheses of Ni-poor (NCM111, LiNi 1/3 Co 1/3 Mn 1/3 O 2 ) and Ni-rich (NCM811 LiNi 0.8 Co 0.1 Mn 0.1 O 2 ) lithium transition-metal oxides (space group R3̅ m) from hydroxide precursors (Ni 1/3 Co 1/3 Mn 1/3 (OH) 2 , Ni 0.8 Co 0.1 Mn 0.1 (OH) 2 ) are investigated using in situ synchrotron powder diffraction and near-edge X-ray absorption fine structure spectroscopy. The development of the layered structure of these two cathode materials proceeds via two utterly different reaction mechanisms. While the synthesis of NCM811 involves a rock salt-type intermediate phase, NCM111 reveals a layered structure throughout the entire synthesis. Moreover, the necessity and the impact of a preannealing step and a high-temperature holding step are discussed.

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“…This is confirmed by the fact that at this point, the diffusion coefficient drops (Figure S5c) and the Ni 2+ content in the bulk ( i.e. , the redox active sites in NCM622) is suppressed to zero (Figure c). ,, …”

Section: Results and Discussionmentioning

confidence: 55%

“…With increasing covalence (Ni 3+ configuration), the Ni–O hybrid peaks at 529 eV and 530 eV increase (Figure b,d, purple circles). ,, At the end of charging, the Ni 2+ /Ni 3+ ratios of the TEY and FY data are nearly aligned with each other, although the ratio decreases significantly upon charging in both cases (Figure a,c).…”

Section: Results and Discussionmentioning

confidence: 78%

“…NEXAFS measurements of Ni L 2.3 , Co L 2.3 , Mn L 2.3 , and O K of the polished samples were carried out in fluorescence yield (FY) detection mode at the Karlsruhe synchrotron light source KARA (Germany). The photon energy resolution was set to 0.2–0.4 eV, and energy calibration (using a NiO reference), dark current subtraction, division by I 0 , background subtraction, data normalization, and absorption correction were performed. ,, …”

Section: Experimental Sectionmentioning

confidence: 99%

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Unraveling the State of Charge-Dependent Electronic and Ionic Structure–Property Relationships in NCM622 Cells by Multiscale Characterization

Jetybayeva

Schön

et al. 2022

ACS Appl. Energy Mater.

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LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) undergoes crystallographic and electronic changes when charging and discharging, which drive the cathode material close to or even beyond its stability window. To unravel the charge compensation mechanism of NCM622, spatially resolved atomic force microscopy (AFM) measurements in electrochemical strain microscopy (ESM) and conductive AFM (C-AFM) modes are obtained, and the spectroscopic information and crystallographic information are compared. All experiments are performed with two sets of samples: state-of-the-art samples that are composed of a binder, a conductive additive, and an active material and polished samples for single-particle analysis. Near-edge X-ray absorption fine structure spectroscopy shows that ionic Ni 2+ reacts to give Ni 3+ when charging and forms covalent bonds with its oxygen neighbors. A Ni 2+ /Ni 3+ gradient across the particles balances out with the increasing state of charge, as verified by ESM. Therefore, the results also provide an important view that improves the mechanistic understanding of ESM in electrode materials. Finally, the interplay between the electronic and ionic conductivities and the crystallinities of NCM622 cathodes is elaborated and discussed.

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Reversible and Irreversible Redox Processes in Li-Rich Layered Oxides

Cited by 21 publications

References 54 publications

Quantifying the Anomalous Local and Nanostructure Evolutions Induced by Lattice Oxygen Redox in Lithium‐Rich Cathodes

Quantifying the Anomalous Local and Nanostructure Evolutions Induced by Lattice Oxygen Redox in Lithium‐Rich Cathodes

Monitoring the Formation of Nickel-Poor and Nickel-Rich Oxide Cathode Materials for Lithium-Ion Batteries with Synchrotron Radiation

Unraveling the State of Charge-Dependent Electronic and Ionic Structure–Property Relationships in NCM622 Cells by Multiscale Characterization

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