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Project titleTowards improved high capacity layered electrode materials for Li-ion batteries through atomic-level understanding of the redox reactions.

AffiliationAutonomous Non-Profit Organization for Higher Education "Skolkovo Institute of Science and Technology",

Research area 03 - CHEMISTRY AND MATERIAL SCIENCES, 03-601 - Chemistry of new inorganic functional and nano-dimensional materials

Keywordslithium-ion battery, cathode, anode, anionic redox, layered oxides, electrode materials, synthesis, crystal structure, electrochemistry, voltage fade, voltage hysteresis, transmission electron microscopy

Annotation
The project targets the important research problem of designing the new generation of the high energy density secondary electrochemical energy sources with the positive electrodes (cathodes) based on Li-rich transition metal oxides, such as Li1.2Ni0.13Mn0.54Co0.13O2 (Li-rich NMC). Demonstrating significantly higher energy density compared to the cathode materials commercially deployed by now, Li-rich NMCs suffer from several drawbacks (voltage fade, voltage hysteresis, sluggish Li intercalation kinetics) hampering their practical applications. This problem will be resolved in this project through a multidisciplinary approach including modern techniques of preparative chemistry, such as digitally-controlled coprecipitation synthesis and/or microwave-assisted hydrothermal synthesis, advanced characterization methods, such as aberration-corrected high angle annular dark field and annular bright field scanning transmission electron microscopy, electron tomography, reciprocal space tomography (also in situ), resonant inelastic X-ray scattering, structural studies with synchrotron X-ray and neutron diffraction, and computational modeling using density functional theory. Material synthesis and investigation will be integrated with well-elaborated electrochemical tests aimed at quantitative evaluation of the degradation effects. The impact of morphology and microstructure on the degradation of the electrochemical properties of Li-rich NMCs will be studied first, in order to separate it from the impact of the crystal structure evolution. Then, on the dedicated model systems, voltage fade and voltage hysteresis after electrochemical cycling will be studied in relation to the transition metal cation migration and oxygen sublattice oxidation with a formation of “peroxogroups”. The last phenomena will be scrutinized in detail, as the reversible oxygen redox is responsible for high electrochemical capacity of Li-rich NMCs, but the detailed mechanism of this redox is still not fully understood. Thanks to the detailed study of both anion- and cation-centered redox processes and concomitant crystal structure rearrangements, novel modified Li-rich chemical compositions will be developed, which are less susceptible to electrochemical degradation upon prolonged cycling. The project results, besides their obvious practical importance, will be of fundamental academic novelty and interest, as they shed light on the relationships between the interrelated transition metal cation migration and partial oxygen oxidation and the reversibility limits for the associated crystal structure transformations upon lithium (de)intercalation. From practical perspectives, the project should open new possibilities for designing new advanced high capacity electrode materials and batteries with higher energy density. The project will be performed in frame of the scientific collaboration between Skolkovo Institute of Science and Technology (Skoltech, Center for Energy Science and Technology) and University of Antwerp (UAntwerpen, the electron microscopy center EMAT). Two research groups are already in long-standing cooperation and will play complementary roles in the project. Skoltech possesses solid competences in the synthesis of electrode materials, electrochemistry, battery cell design, crystallography and computational methods, whereas UAntwerpen holds unique competences and equipment in the field of transmission electron microscopy, particularly in extracting quantitative information on the atomic structure, electronic structure and local chemistry from the TEM data. Close collaboration of two research groups will give rise to remarkable synergetic effect resulting in a new level of understanding of the reversible lithium intercalation in complex transition metal oxides.

Expected results
The project will establish the relationships between the degradation of the electrochemical working parameters (first of all, voltage fade and voltage hysteresis) of the Li-rich high capacity layered complex oxides of Ni, Mn and Co with the general composition Li4/3-xNi2+xMn4+2/3-xCo3+xO2, reversible and irreversible changes of the atomic structure of these oxides and the redox reactions occurring upon lithium (de)intercalation. The crystal structure fragments stabilizing partially oxidized forms of oxygen at high electrode potentials will be identified, and their influence on the formation of transition metal cation vacancies and migration of the transition metal cations to the vacant Li positions will be investigated, along with the reversibility of this migration and its relation to the electrochemical cycling parameters. In order to achieve this goal, the sample of dedicated model systems will be synthesized and electrochemically tested. The model systems will be selected which allow for varying an interaction of the cationic and anionic sublattices, and crystal structure dimensionality. With the help of the coprecipitation synthesis technique and microwave-assisted hydrothermal technique the samples of the Li-rich layered oxides with well-controlled and variable microstructure will be prepared in order to separate contributions of the microstructure and atomic structure evolution into electrochemical degradation that will be done with the quantitative investigation of the microstructural evolution with electron tomography. Ab initio computational investigation of energy barriers for transition metal cation migration will lead to possible pathways towards chemical modification of the layered oxides in order to make this migration as reversible as possible. As a result, Li-rich layered oxides with advanced chemical compositions will be prepared, demonstrating high energy density (> 1000 Wth/kg) and stable electrochemical cycling with high voltage retention, minimal hysteresis and improved rate capability. In general, the anticipated results will be of high fundamental and practical importance. The fundamental knowledge on the redox reactions in the anion sublattice at (de)intercalation of the alkali cations can be used in the future for developing high capacity cathodes based on non-oxide chemistries (polyanion sulfides, oxonitrides etc.), whereas the methodology of multiscale investigation of the electrode structure can be equally employed for studying other cathode materials (spinels, polyanionic substances), as well as the materials for Na-ion and K-ion batteries. The project results will be published in research articles in the leading international journals, including Chemistry of Materials, Inorganic Chemistry, Journal of Materials Chemistry A, Angewandte Chemie, Advanced Energy Materials, Journal of Power Sources and others. The intellectual property created in course of the project will be adequately protected. The practical importance of the project results stems from the prospects to design Li-ion batteries with enhanced energy density that is particularly important for electromobiltity where the energy stored in the battery defines the mileage of the car. The immediate practical implementation of the results can be realized through the “RUSTOR”, the Skolkovo resident, which is specialized on production of the advanced electrode materials.

Annotation of the results obtained in 2022
During the third stage of the project, studying the structural features of Li2+xMo1-xO3 (the chemical composition was proposed for the first time by the authors of this project in the previous reporting period) was continued. In particular, the crystal structure of Li2+xMo1-xO3 has been clarified and the unit cell parameters have been refined, as well as the compositional range of the solid solutions has been determined. The chemical compositions of Li2+xMo1-xO3 were estimated based on the cR/aR ratio and the value of x. Thus, the obtained Li2+xMo1-xO3 samples can be divided into three groups according to their chemical composition. As a result of the TEM study of the Li2+xMo1-xO3 local structure, a structural model with homogeneous distribution of Mo3 clusters in the (Li/Mo)O6 layer compatible with local electroneutrality and chemical composition was proposed. The suggested model was confirmed using theoretical calculations by modeling STEM images. Applying the DPC technique made it possible to visualize the atomic structure of triangular Mo3O13 clusters. DFT calculations predicted a stepwise form of the first charge galvanostatic curve of Li2+xMo1-xO3 with the presence of two pseudo-plates, similar to Li-rich layered oxides, as a consequence of two successive processes: oxidation of triangular Mo3 clusters to Mo2 dimers and then oxidation of dimers with a complete Mo-Mo bond break. In order to confirm the results obtained via DFT calculations, a TEM study of the local crystal structure of Li2+xMo1-xO3 at different states of charge was carried out. Within the DFT study, it was found that Ru in the model system xLi2RuO3-(1-x)Li1.2Ni0.2Mn0.6O2 has a protective effect on oxygen atoms, and this effect extends not only to oxygen atoms directly involved in the formation of Ru-O bonds, but also to oxygen atoms forming Ni-O and Mn-O bonds. Based on Li2Mn1-xTixO3 (x = 0-0.2) model compound, using a combination of both experimental and calculation methods, an interplay between the tendency to form O-O dimers, the stabilization of dimers with toward the evolution of O2, and the occupation of the d-orbital of metals included in Li-rich oxides was established, i.e. the relative content of Mn and dopant (Ti4+). According to DFT calculations, the process of charge transfer between oxygen and nickel in Li-rich oxides can occur either with a large barrier compared to electron transfer between two transition metals, or spontaneously at high degrees of deintercalation, when lithium is extracted from positions in the transition metal layer, forming Vac-O-Vac configurations. The results of the third stage of the project have been published in two articles in peer-reviewed journals of the first quartile (Q1). The results were presented in 11 reports at scientific conferences.

Publications

1. Morozov A.V, Moiseev I.A., Savina A.A., Boev A.O., Aksyonov D.A., Zhang L., Morozova P.A., Nikitina V.A., Pazhetnov E.M., Berg E.J., Fedotov S.S., Tarascon J.-M., Antipov E.V., Abakumov A.M. Retardation of Structure Densification by Increasing Covalency in Li- Rich Layered Oxide Positive Electrodes for Li-Ion Batteries Chemistry of materials, 34, 15, 6779–6791 (year - 2022) https://doi.org/10.1021/acs.chemmater.2c00921

2. Savina A.A., Saiutina V.V., Morozov A.V., Boev A.O., Aksyonov D.A., Dejoie C., Batuk M., Bals S., Hadermann J., Abakumov A.M. Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li2+xMo1−xO3 Solid Solutions Inorganic Chemistry, 61, 14, 5637–5652 (year - 2022) https://doi.org/10.1021/acs.inorgchem.2c00420

Annotation of the results obtained in 2020
At first year of the project, the detailed investigation of microstructural architecture of Li-rich NMC prepared by co-precipitation followed by high-temperature annealing with various Li precursors was selected as a primary direction. We found that as-prepared materials consist of spherical agglomerates, which in turn are built of radially distributed columnar elements comprising primary rectangular-shaped submicron crystallites. The coherent intergrain boundaries demonstrate enlarged interplanar distances, resulting in the incoherent character of intergrain boundaries along the direction of columnar elements causing displacement and deformation of the atomic layers. The cation layers along the coherent boundaries are enriched with Co and depleted with Mn, whereas incoherent intergrain boundaries do not show noticeable deviation in chemical composition. We developed and optimized hydrothermal co-precipitation of mixed carbonate precursors, including microwave-activated hydrothermal approach to prepare Li-rich layered oxides. We studied the influence of Li source on the distribution of transition metal cations over the primary particles of cathode material and microstructure of secondary agglomerates formed in the hydrothermal synthesis. The model systems based on the Li2MoO3 и Li5OsO6 structures were prepared. The chemical composition of Mo-based material could be written as Li2+xMo1-xO3, while the formation and type of the superstructure existing due to Mo-Mo bonds depends on the chemical composition and annealing temperature. We developed the synthesis of Li5OsO6 and its Mg-substituted analogues and synthesized phase-pure monoclinic modification of Li4MgOsO6. For the first time, the differential phase contrast method at extremely low electron dose was applied for visualization with atomic resolution of the crystal structure of cathode materials in the different state of charge. We investigated the impact of Nb- and Ru-substitution on the structural and electrochemical behavior of Li1.2Ni0.2Mn0.6O2 layered cathode materials, demonstrated for substituted compounds the formation of layered structure with superstructure ordering and carried out the analysis of chemical composition and spatial distribution of the metal cations. Galvanostatic cycling curves of the prepared cathode materials exhibit partial suppression of voltage fade effect compared to pristine Li1.2Ni0.2Mn0.6O2. The method of protective “core-shell” coating was developed for Li1.17Ni0.17Mn0.50Co0.17O2 layered oxide acting as a core and another cathode material with spinel structure used as a shell. The composite cathode material modified in this way exhibits enhanced electrochemical properties compared to pristine material without coating. The fundamental problem of high irreversibility observed on the first cycle for Li-rich NMC materials was understood as a complex process, starting from oxidation of Ni2+ and Co3+ to Ni4+ and Co4+, respectively, and further partial oxidation of oxygen sublattice accompanied by migration of Mn cations in the structure up to 4.6 V. The process is finalized by the evolution of gaseous O2 between 4.6 and 4.8 V. During discharge, both cationic and anionic sublattices are reduced together, what leads to change of shape of galvanostatic curve from “ladder” on the first cycle to S-shaped on the discharge and all further cycles. DFT calculations of migration barriers for the model system LixMnO3 were performed depending on the lithium concentration, and the effect of substitution of Mn by Ni and Co on migration barriers was also considered. It was found that, in the charged state (х = 0.25), the migration of Mn in the Li position inside the d-metal layer is a thermodynamically favorable process with a simultaneous decrease in the barrier to ion migration, while the migration of Ni and Co requires overcoming higher barriers; therefore, Ni and Co should provide stabilizing effect. In the discharged state, migration of Mn from the d-metal layer to the Li layer is possible. The results obtained make it possible to explain the voltage fade during the cycling of Li-rich NMC. The abovementioned results were used to construct the general model of stabilization of electronic structure of oxidized anionic states in the layered cathode materials with reversible oxidation of oxygen sublattice. The results of work were published in three papers in peer-reviewed journals with high impact factor (Q1).

Publications

1. Andrey Shevtsov, Haixiang Han, Anatolii Morozov, Jesse C. Carozza, Aleksandra A. Savina, Iaroslava Shakhova, Nellie R. Khasanova, Evgeny V. Antipov, Evgeny V. Dikarev, Artem M. Abakumov Protective Spinel Coating for Li1.17Ni0.17Mn0.50Co0.17O2 Cathode for Li-Ion Batteries through Single-Source Precursor Approach NANOMATERIALS, Nanomaterials 10, 1870, (2020) (year - 2020) https://doi.org/10.3390/nano10091870

2. Wei Yin, Alexis Grimaud, Gwenaelle Rousse, Artem M. Abakumov, Anatoliy Senyshyn, Leiting Zhang, Sigita Trabesinger, Antonella Iadecola, Dominique Foix, Domitille Giaume, Jean-Marie Tarascon Structural evolution at the oxidative and reductive limits in the first electrochemical cycle of Li1.2Ni0.13Mn0.54Co0.13O2 NATURE COMMUNICATIONS, Nat Commun 11, 1252 (2020). (year - 2020) https://doi.org/10.1038/s41467-020-14927-4

3. Artem M. Abakumov, Stanislav S. Fedotov, Evgeny V. Antipov, Jean-Marie Tarascon Solid state chemistry for developing better metal-ion batteries NATURE COMMUNICATIONS, Nat Commun 11, 4976 (2020) (year - 2020) https://doi.org/10.1038/s41467-020-18736-7

4. - Профессора Сколтеха о роли химии твердого тела в создании металл-ионных аккумуляторов Вебсайт РНФ, - (year - )

Annotation of the results obtained in 2021
As part of the second stage of the project, 3D reconstruction of volumetric models of material particles and pore space was carried out using Slice & View technology for three Li1.2Ni0.13Mn0.54Co0.13O2 samples with different microstructural organization. Based on the results obtained, it was concluded that the choice of a lithium source in the process of obtaining cathode materials based on Li-enriched NMC is of decisive importance in the formation of one or another microstructural organization of secondary agglomerates. A quantitative assessment of the porosity of secondary agglomerates with different microstructural organization has been carried out. In the high-resolution TEM mode, coherent grain boundaries along the (001) crystallographic plane discovered during the previous stage of the project were visualized and studied. Analysis of the spatial distribution of the chemical composition near these grain boundaries by the EDS-STEM method with atomic resolution showed that Na atoms tend to segregate at (001) twin boundaries. It was found that the close-packing mode of the oxygen sublattice changes near the twin boundary, providing trigonal-prismatic coordination of segregated Na cations, which leads to the formation of a P2 block at the grain boundary. DFT modeling confirmed the thermodynamic advantage of the formation of twin boundaries with the segregation of sodium and cobalt in Li-enriched layered oxides. Calculations of migration barriers have shown that such boundaries negatively affect the diffusion of lithium across the (001) grain boundaries. Using the model system xLi2RuO3- (1-x) Li1.2Ni0.2Mn0.6O2 (x = 0-0.1), we studied the effect of the M-O bond covalence on the electrochemical characteristics of Li-rich NMCs. The study of electrochemical properties by galvanostatic cycling, voltammetry, galvanostatic intermittent titration and electrochemical mass spectrometry, as well as the study of the evolution of the crystal and electronic structure of compounds at different stages of cycling by HAADF-STEM, STEM-EELS, XAS and XRF showed the suppression of irreversible Mn4 + oxygen oxidation and reduction during the first activation and subsequent cycles and the slowing down of the formation of a "compacted" structure on the surface and its growth deep into the crystallites with an increase in the covalence of the M-O bond. In this case, with an increase in the covalence of the M-O bond, a decrease in the reversible discharge capacity was observed due to the inhibition of the redox activity of Mn4+/3+/2+. The study of solid solutions Li2+xMo1-xO3 by synchrotron X-ray diffraction in a wide temperature range was carried out, which showed that Li2+xMo1-xO3 undergoes two disproportionation reactions upon heating. It was found that the structural features, depending on the annealing temperature, have a significant effect on the electrochemical properties of Li2+xMo1-xO3. Most of the irreversible structural changes occur during the first charge cycle, with the charging and discharging curve profiles changing sharply after the first cycle. However, the drop in operating potential after 30 cycles (1.5-4.0 V vs Li/Li+) was found to be negligible compared to the observed gradual drop in operating voltage in Li-rich NMCs. The crystal structure of Li4MgOsO6 was studied using TEM methods. It was found that the heterovalent substitution of Mg for Li made it possible to change the oxidation state of Os, but led to a partial disordering of the structure and suppression of inverted honeycomb ordering. The study of the structure of NaLi1/3Mn2/3O2 at various stages of cycling in Na- and Li-half-cells by HAADF-STEM made it possible to unambiguously link the phenomenon of irreversible interlayer cationic migration with the effect of a decrease in the operating voltage during long-term cycling of Li-enriched layered oxide cathode materials. Also, the study of Li1.17Ti0.33Fe0.5O2 using HAADF-STEM showed that cation migration is not the main cause of the working potential hysteresis, and the nature of the hysteresis lies in the delayed kinetics of one-electron transfer between the metal and the ligand, which was explained within the framework of the Marcus theory. The results of the second stage of the project were published in three articles in peer-reviewed journals included in the first quartile (Q1) and presented in 11 reports at scientific conferences.

Publications

1. A.M. Abakumov, C. Li, A. Boev, D.A. Aksyonov, A.A. Savina, T.A. Abakumova, G. Van Tendeloo, S. Bals Grain boundaries as a diffusion-limiting factor in Li-rich NMC cathodes for high energy Li-ion batteries ACS Appl. Energy Mater., 4, 7, 6777–6786 (year - 2021) https://doi.org/10.1021/acsaem.1c00872

2. B. Li, M.T. Sougrati, G. Rousse, A.V. Morozov, R. Dedryvère, A. Iadecola, A. Senyshyn, L. Zhang, A.M. Abakumov, M.-L. Doublet, J.-M. Tarascon Correlating ligand-to-metal charge transfer with voltage hysteresis in a Li-rich rock-salt compound exhibiting anionic redox Nature Chemistry, vol.13, p. 1070–1080 (year - 2021) https://doi.org/10.1038/s41557-021-00775-2

3. Q. Wang, S. Mariyappan, G. Rousse, A.V. Morozov, B. Porcheron, R. Dedryvère, J. Wu, W. Yang, L. Zhang, M. Chakir, M. Avdeev, M. Deschamps, Y.-S. Yu, J. Cabana, M.-L. Doublet, A.M. Abakumov, J.-M. Tarascon Unlocking anionic redox activity in O3-type sodium 3d layered oxides via Li substitution Nature Materials, Vol. 20, p. 353–361 (year - 2021) https://doi.org/10.1038/s41563-020-00870-8