Cation-disordered Rocksalt Research Articles

Coherent-Precipitation-Stabilized Phase Formation in Over-Stoichiometric Rocksalt-Type Li Superionic Conductors.

Rationalizing synthetic pathways is crucialformaterialdesignand property optimization, especially for polymorphicandmetastable phases. Over-stoichiometric rocksalt (ORX) compounds,characterized by their face-sharing configurations, are a promising group of materials with unique properties; however, their development is significantly hindered by challenges in synthesizability. Here, taking the recently identified Li superionic conductor, over-stoichiometric rocksalt Li-In-Sn-O (o-LISO) material as a prototypical ORX compound, the mechanisms of phase formation are systematically investigated. It is revealed that the spinel-like phase with unconventional stoichiometry forms as coherent precipitate from the high-temperature-stabilized cation-disordered rocksalt phase upon fast cooling. This process prevents direct phase decomposition and kinetically locks the system in a metastable state with the desired face-sharing Li configurations. This insight enables us to enhance the ionic conductivity of o-LISO to be >1mScm-1 at room temperature through low-temperature post-annealing. This work offers insights into the synthesis of ORX materials and highlights important opportunities in this new class of materials.

Structural, Electrochemical, and (De)lithiation Mechanism Investigation of Cation-Disordered Rocksalt and Spinel Hybrid Nanomaterials in Lithium-Ion Batteries.

Significant demand for lithium-ion batteries necessitates alternatives to Co- and Ni-based cathode materials. Cation-disordered materials using earth-abundant elements are being explored as promising candidates. In this paper, we demonstrate a coprecipitation synthetic approach that allows direct preparation of disordered rocksalt Li2.4Fe1.0Ti1.0O4.7 (r-LFTO·C) and spinel structured hybrid Li0.5Fe1.0Ti0.9O3.2·C (s-LFTO·C) nanoparticles with a conformal conductive carbon coating. High-angle annular dark-field imaging coupled with electron energy loss spectroscopy mapping shows uniform Fe/Ti distribution with minor compositional variation among particles. Cation disorder was confirmed for both of the materials at an atomic level, with a short-range order more pronounced in r-LFTO·C. Operando X-ray absorption spectroscopy, ex situ hard X-ray photoelectron spectroscopy, ex situ soft X-ray absorption spectroscopy, and ex situ synchrotron X-ray diffraction were used to investigate (de)lithiation in the bulk and at the surface. Structurally, the r-LFTO·C demonstrated reversible partial Fe center migration between octahedral and tetrahedral sites during (de)lithiation. The r-LFTO·C evidenced that the redox of O was coincident with iron redox during initial electrochemical cycling, while iron redox dominated later cycling. In contrast, s-LFTO·C electrochemistry involved iron redox throughout the cycling process. The findings rationalize the differences in the electrochemistry where r-LFTO·C shows higher initial capacity yet poorer capacity retention over a voltage window where O redox can be accessed, while the s-LFTO·C shows lower initial capacity yet improved capacity retention.

(Invited) Mn-Based High-Energy Cathodes for Lithium-Ion Batteries

Cation-disordered Li-excess rocksalts (DRX) are promising cathode materials for next-generation lithium-ion batteries utilizing sustainable resources. [1] These compounds are typically Co- and Ni-free, and they offer exceptionally large charge storage capacities by activating the redox reactions of both cationic transition-metals and anionic oxygen in the lattice. [2-4] Recent studies showed that significant performance improvement can be achieved by introducing fluorine substitution. Fluorine was found to improve local structural stability and chemomechanical properties, as well as reduce oxygen gas release, impedance rise and capacity fade. [5-7] However, achieving adequate cycle life remains a formidable barrier in DRX cathodes.In this presentation, we will show our recent effort in developing stable DRX oxyfluorides based on Mn-redox chemistry. Mn-rich DRX oxyfluoride cathodes consisting of earth-abundant elements will be presented. These materials experience unique local structural transformations upon charge and discharge, leading to dynamic evolution in voltage profile and significant capacity rise during early cycles. Stable cycling can be achieved after the initial activation process. Our understanding in how chemistry can impact local and long-range structures and their evolution during electrochemical cycling will also be presented, as well as the perspectives on future directions in cathode development. References Chen D.; Ahn J.; Chen, G. An Overview of Cation-Disordered Lithium-Excess Rocksalt Cathodes. ACS Energy Lett. 2021, 6, Lee, J.; Urban, A.; Li, X.; Su, D.; Hautier, G.; Ceder, G. Unlocking the Potential of Cation-Disordered Oxides for Rechargeable Lithium Batteries. Science 2014, 343, 519.Yabuuchi, N.; Takeuchi, M.; Nakayama, M.; Shiiba, H.; Ogawa, M.; Nakayama, K.; Ohta, T.; Endo, D.; Ozaki, T.; Inamasu, T.; Sato, K.; Komaba, S., High-Capacity Electrode Materials for Rechargeable Lithium Batteries: Li3NbO4-based System with Cation-Disordered Rocksalt Structure. Natl. Acad. Sci. 2015, 112, 7650.Chen, D.; Kan, W. H.; Chen, G. Understanding Performance Degradation in Cation-Disordered Rock-Salt Oxide Cathodes. Energy Mater. 2019, 9, 1901255.Lee, J.; Papp, J. K.; Clément, R. J.; Sallis, S.; Kwon, D.-H.; Shi, T.; Yang, W.; McCloskey, B. D.; Ceder, G. Mitigating oxygen loss to improve the cycling performance of high capacity cation-disordered cathode materials. Commun. 2017, 8, 981.Lun, Z.; Ouyang, B.; Kitchaev, D. A.; Clément, R. J.; Papp, J. K.; Balasubramanian, M.; Tian, Y.; Lei, T.; Shi, T.; McCloskey, B. D.; Lee, J.; Ceder, G. Improved Cycling Performance of Li-Excess Cation-Disordered Cathode Materials upon Fluorine Substitution. Energy Mater. 2018, 9,1802959.Ahn, J.; Chen, D.; Chen, G.. A Fluorination Method for Improving Cation-Disordered Rocksalt Cathode Performance. Energy Mater. 2020, 10, 2001671.

Understanding High Voltage Electrolyte Reactivity on Cation-Disordered Rock Salt Cathodes

Li-ion battery demand is expected to increase dramatically to meet rapidly increasing energy storage demands. To address the expense and scarcity of cobalt and nickel used in current layered oxide cathodes, alternative cathode materials that rely on earth-abundant transition metals must be explored. Promising such materials are cation-disordered rocksalt (DRX) oxides, particularly those that are comprised of manganese and titanium, along with lithium excess to allow for high reversible capacities (>300 mAh/g). A substantial fraction of extractable lithium capacity in DRX materials occurs at high voltages, creating high energy density, but also leading to deleterious degradation processes. Recent studies have observed reactivity of the DRX surface when cycled to high voltages: >25% of transition metals migrating out of the cathode and continuous evolution of CO2 after 150 cycles [1]. 13C labeling has identified the carbonate electrolyte as the primary source of the CO2 after the first cycle [2]. This reactivity leads to a sharp increase in impedance and rapid capacity fade [1]. However, the exact cause of high voltage reactivity is still not fully understood for the electrolyte – DRX interface.In this study, we quantify the surface reactivity of select electrolyte – DRX systems using operando gas measurements and inductively coupled plasma – optimal emission spectrometry (ICP-OES). Through this method, we can identify what electrolyte and DRX properties have the largest influence on surface reactivity. To monitor surface reactivity of the electrolyte, differential electrochemical mass spectrometry (DEMS) was used to quantify evolution of CO2 and other gaseous products during cycling. To track the surface reactivity of the DRX, ICP-OES was used to quantify transition metal dissolution. We show that ethylene carbonate oxidation is particularly problematic above 4.4 V, and that processes involving the conductive carbon, as well as Mn and O redox are culpable. The results of this study provide insight into the primary causes of capacity fade in DRX-based batteries, informing future designs of the electrolyte, DRX, and other cathode materials.[1]: Matthew J. Crafton et al 2024 J. Electrochem. Soc. 171 020530[2]: Manuscript in Preparation: Tzu-Yang Huang et al 2024. Chem. Of Mat. (Manuscript ID: cm-2024-007563)

Localized High-Concentration Electrolytes for High-Voltage Disordered Rocksalt Cathode Materials

With the pursuit of high energy-density battery systems, cathode materials with high specific capacity and high working voltage are of high interest. Among the transition metal oxide cathode materials, lithium (Li)-rich cation disordered rock salt (DRX) cathode materials are promising candidates for next-generation high-energy-density Li batteries because they offer high specific capacities and cost benefits. Particularly, the manganese (Mn)-based DRXs show more promise due to the utilization of earth abundant material and good thermal stability of Mn. However, these cathodes often face big challenges when cycled in the state-of-the-art LiPF6/carbonate-based electrolytes at voltages up to 4.8 V. These include severe side reactions between the cathode and the electrolyte, transition metal dissolution and structural instability of the cathode particles, all of which result in fast capacity fading. In this work, we developed advanced localized high-concentration electrolytes (LHCEs) to mitigate these problems and enable stable cycling of a DRX cathode material, Li1.2Mn0.6Ti0.2O2 (LMTO). The LHCEs demonstrate high voltage stability of 4.9 V vs. Li/Li+ and capability of forming an ultrathin and stable cathode-electrolyte interphase. Consequently, Li||LMTO half cells with the optimal LHCE exhibit increased capacity, enhanced cycling stability and superior rate capability when compared to the cells with the conventional electrolyte. This work sheds the light of electrolyte development to enable practical DRX cathode-based high-energy Li batteries.

Electrochemistry and Cycling Dependent Structural Analysis of High and Low Mn Based Disordered Rocksalt Cathodes for Lithium-Ion Batteries

Cobalt-free cation-disordered rocksalt (DRX) materials have recently emerged as a class of next-generation high-capacity cathodes for lithium-ion batteries which can incorporate earth abundant, low-cost elements such as Mn and Ti. One of the reasons for their enhanced performance is due to the presence of percolating lithium rich clusters which enable facile lithium transport. Structural phenomena such as cation short-range ordering and phase transformations in DRX materials at small length scales are known to dramatically impact local Li clusters and hence the Li diffusion channels, Li transport, and hence electrochemical properties of DRX cathodes. Recently, Mn-rich DRX materials (Mn/Ti ratio >1) have shown to phase transform upon extended cycling, resulting in improved capacity and rate performance in these materials. Therefore, it is crucial to understand the nature of the DRX structure as a function of cycling to maximize the performance in DRX materials. Interestingly, these phase changes are not observed in DRX with a low Mn content (Mn/Ti ratio <1). Keeping this in mind, the goal of this research is to understand the structural changes during electrochemical cycling and investigate the differences in electrochemical properties (Li ion transport, rate capability, cycling) in high and low Mn DRX cathodes. In addition to the electrochemical characterization, a suite of material characterization techniques such as X-ray diffraction, X-ray absorption Spectroscopy, and pair distribution function analysis, are used to perform in depth cycling dependent structural analysis and compared between the high Mn and low Mn DRX compositions. Overall, this study and poster presentation will discuss key scientific insights related to the cycling induced phase transformation and electrochemical performance of Mn-Ti based DRX cathodes. Based on these results, further investigations into synthetic manipulation of the DRX structure can be performed to utilize the full potential of the newly formed phase upon cycling.

Structural Origins of High Performance in Partially Disordered Li- and Mn-Rich Cathodes

The discovery of Li-excess cation-disordered rocksalt (DRX) cathodes lifts the restriction on a specific Li-TM ordering to enable the exploration of cathode materials in a chemical space of earth abundant materials. Recently, phase transformation in disordered Li- and Mn-rich rock-salts (Li1.05Mn0.85Ti0.1O2) have been shown to form high energy density, capacity retention and rate capability cathode materials (named delta) with partial Spinel-like ordering at short coherence lengths.1 However, atomic scale structural features of the material which determine its high performance such as extent of disordering and Li-transport pathways are not well-understood yet. We first perform symmetry analysis to reveal aspects of the transformation which are central to the nanoscale domain formation in the delta phase and crucial for characterizing its structure. We develop a simple structural order parameter to distinguish the Spinel-like ordering from the disordered rocksalt (DRX) structure, characterizing the extent of disordering, sizes and spatial location of the domains as the transformation proceeds. We perform multi time-scale Kinetic Monte Carlo Simulations for understanding the DRX-to-delta transformation. Our results reveal both thermodynamic and kinetic factors causing the formation of spinel-like nano domains and spatial distribution of Ti and Li-excess in the delta phase of Li1.05Mn0.85Ti0.1O2, providing key insights into its high rate capability. Our simulations reveal principles for designing the structure at nanoscale and electrochemical performance through changes in composition. Cai, Z.; Ouyang, B.; Hau, H.-M.; Chen, T.; Giovine, R.; Koirala, K. P.; Li, L.; Ji, H.; Ha, Y.; Sun, Y.; Huang, J.; Chen, Y.; Wu, V.; Yang, W.; Wang, C.; Clément, R. J.; Lun, Z.; Ceder, G. In Situ Formed Partially Disordered Phases as Earth-Abundant Mn-Rich Cathode Materials. Nat. Energy 2023, 1–10. https://doi.org/10.1038/s41560-023-01375-9.

Accelerating the Electrochemical Formation of the δ Phase in Manganese-Rich Rocksalt Cathodes

Recently, advancements in Mn-based disordered rocksalt (DRX) cathodes have demonstrated not only high energy density but also an electrochemical transformation to a spinel-like phase, now referred to as the δ phase1,2,3. The δ phase possesses a unique domain structure, a flattened voltage profile and improved rate capability. However, two important challenges remain: the necessity to mill the material to reduce particle size after synthesis, and the prolonged cycling required to complete the transformation to spinel-like partial order. To address these challenges, we present the development of an electrochemical formation method that enables rapid and in-situ formation of this partially disordered spinel phase from a DRX cathode, including in micron-sized single crystals.To gain a deeper understanding of this transformation process, we carry out a systematic study to determine whether the transformation to the δ phase can be accelerated through a precycling formation process. By employing this novel electrochemical approach to purposefully stimulate the transformation, we successfully reduce the time required from several weeks to as little as one day for Mn-rich DRX. Extended cycling and synchrotron X-ray diffraction confirm that these materials exhibit both equivalent performance and resulting structure to those obtained through conventional cycling over a much longer duration. Further characterization of this material using HAADF and 4-D STEM reveals the complex local structure of the spinel-like partial ordering. It is hoped that such a practical electrochemical formation method allows for an acceleration of research on these earth-abundant and energy-dense materials. Li, L.; Lun, Z.; Chen, D.; Yue, Y.; Tong, W.; Chen, G.; Ceder, G.; Wang, C. Fluorination-Enhanced Surface Stability of Cation-Disordered Rocksalt Cathodes for Li-Ion Batteries. Adv Funct Mater 2021, 31 (25), 2101888. https://doi.org/10.1002/adfm.202101888.Ahn, J.; Giovine, R.; Wu, V. C.; Koirala, K. P.; Wang, C.; Clément, R. J.; Chen, G. Ultrahigh-Capacity Rocksalt Cathodes Enabled by Cycling-Activated Structural Changes. Adv. Energy Mater. 2023. https://doi.org/10.1002/aenm.202300221.Cai, Z.; Ouyang, B.; Hau, H.-M.; Chen, T.; Giovine, R.; Koirala, K. P.; Li, L.; Ji, H.; Ha, Y.; Sun, Y.; Huang, J.; Chen, Y.; Wu, V.; Yang, W.; Wang, C.; Clément, R. J.; Lun, Z.; Ceder, G. In Situ Formed Partially Disordered Phases as Earth-Abundant Mn-Rich Cathode Materials. Nat. Energy 2023, 1–10. https://doi.org/10.1038/s41560-023-01375-9.

(Invited) Nanostructured Positive Electrode Materials for Li-Ion Battery Applications

Ni-enriched layered materials are used as electrode materials of Li-ion batteries for electric vehicle applications. Stoichiometric LiNiO2 with cationic Ni3+/Ni4+ redox is the ideal electrode material, but the gradual loss of capacity at the high voltage region, associated with Ni ion migration, hinders its use for practical applications.1 Recently, the importance of non-stoichiometry and anti-site defects is discussed for LiNiO2, and highly reversible pure Ni-based layered materials without metal substitution is successfully developed through defects engineering.1 Another important target is the development of a practical and high-energy Co-/Ni-free Mn-based positive electrode material, which is necessary for the economical electric vehicles. Nanostructured Mn-based electrode materials are proposed as emerging materials for this purpose.2 However, these materials are generally synthesized by high-energy milling, which cannot be adopted for mass production. Recently, nanostructured LiMnO2 with high-energy density (~800 Wh kg–1) is successfully synthesized by using a conventional calcination reaction, which is potentially used for economical electric vehicle applications.3 To develop safe and high-energy Li-ion batteries, the use of solid electrolyte is an important strategy. Nevertheless, inevitable volume changes of electrode materials on cycling lead to the difficulty to maintain the stable interface between electrode materials and electrolyte. Recently, a nanostructured cation-disordered rocksalt oxide with a dimensionally invariable character is developed. Indeed, the excellent reversibility with solid electrolyte is achieved.5 From these results, the importance of nano-structured lithium insertion materials for practical Li-ion battery applications is discussed.References1) Konuma et al., and N. Yabuuchi, Energy Storage Materials, 66, 103200 (2024).2) Kanno et al., and N. Yabuuchi, ACS Energy Letters, 8, 2753 (2023).3) Miyaoka et al., and N. Yabuuchi, submitted4) R. Fukuma et al., and N. Yabuuchi, ACS Central Science, 8, 775 (2022).5) I. Konuma et al., and N. Yabuuchi, Nature Materials, 22, 225 (2023).

Cycling Performance Research on Disordered Rock Salt Cathode Material in Lithium Ion Batteries

A worldwide effort is presently underway to develop electric vehicles (EVs) or hybrid electric vehicles (HEVs) to reduce fossil fuel consumption in the transportation area. Lithium-ion batteries are the first choice to be used in EVs and HEVs due to their high energy and power density in the existing commercial battery eco-system. With the ever growing EV market, lithium ion battery manufacturers and researchers are facing many challenges, one of which, is how to cut down the metals in the cathode which are rare, expensive, and unbenign to the environment. Over past few years, cobalt-free is a popular topic in the cathode materials research and development effort. Under this topic, disordered rock salt (DRX) cathode materials, that were invented in recent years, have been attracting interest due to their potential high capacity and high energy-density compared with current commercial cathode materials. In the DRX materials, a disordered arrangement of cation species is established, which imparts the DRX materials with its unique lithium transport properties and small volume changes during charge–discharge cycling [1]. Disordered arrangement of cation species also leads to the sloping voltage profile which makes the capacity of the DRX materials dependent on the cut-off voltage. In this research the effect of cut-off voltage on the electrochemical performance of Li1.2Mn0.6Ti0.2O1.8F0.2 DRX was investigated along with the long-term cycling performance.Figure 1. The cycling performance of Li1.2Mn0.6Ti0.2O1.8F0.2/Li half cells with different test protocols.Reference[1] R. J. Clement, Z. Lun and G. Ceder. Cation-disordered rocksalt transition metal oxidesand oxyfluorides for high energy lithium-ion cathodes, Energy Environ. Sci., 2020,13, 345-373. Figure 1

Screening Na-Excess Cation-Disordered Rocksalt Cathodes with High Performance.

The practical application of Na-ion cathode materials is currently restricted by their low energy density and sluggish dynamics, while the cation-disordered rocksalt (DRX) structures offer a possible solution to the challenge. In this study, among the 24 candidates containing d0 elements, we use mixing temperature as a descriptor to screen the synthesizable Na-excess DRX, and we have identified Na1.2Mn0.4Mo0.4O2 as the most promising candidate that exhibits a Na percolating fraction of 53%, which is higher than that of Li1.2Mn0.4Ti0.4O2 (35%) proposed in the previous study due to the larger lattice constant in Na-excess DRX cathodes. More importantly, Na1.2Mn0.4Mo0.4O2 is predicted to have a capacity of 228 mAh/g with an energy density of 552 Wh/kg derived from percolation theory and cluster-expansion Monte Carlo simulations, which is higher than that of Na1.3Nb0.3Mn0.4O2 and Na1.14Mn0.57Ti0.29O2 synthesized recently. For a better understanding, the redox mechanism is explored, which involves Mo4+/Mo6+, Mn3+/Mn4+, and O2-/On- (0 < n < 2), indicating the participation of anionic redox. Meanwhile, the Na+ diffusion prefers a divacancy mechanism via an o-t-o diffusion channel with a low diffusion barrier of 0.29 eV. This study expands the family of DRX for the cathode of Na-ion batteries with enhanced performance.

Thin film synthesis, structural analysis, and magnetic properties of novel ternary transition metal nitride MnCoN2

Recent high-throughput computational searches have predicted many novel ternary nitride compounds providing new opportunities for materials discovery in underexplored phase spaces. Nevertheless, there are hardly any predictions and/or syntheses that incorporate only transition metals into new ternary nitrides. Here, we report on the synthesis, structure, and properties of MnCoN2, a new ternary nitride material comprising only transition metals and N. We find that crystalline MnCoN2 can be stabilized over its competing binaries, and over a tendency of this system to become amorphous, by controlling growth temperature within a narrow window slightly above ambient condition. We find that single-phase MnCoN2 thin films form in a cation-disordered rocksalt crystal structure. X-ray photoelectron spectroscopy analysis suggests that MnCoN2 is sensitive to oxygen through various oxides and hydroxides binding to cobalt on the surface. X-ray absorption spectroscopy is used to verify that Mn3+ and Co3+ cations exist in an octahedrally coordinated environment, which is distinct from a combination of CoN and MnN binaries and in agreement with the rocksalt-based crystal structure prediction. Magnetic measurements suggest that MnCoN2 has a canted antiferromagnetic ground state below 10 K. We extract a Weiss temperature of θ=−49.7K, highlighting the antiferromagnetic correlations in MnCoN2. Published by the American Physical Society 2024

Interfacial deterioration in highly fluorinated cation-disordered rock-salt cathode: Carbonate-based electrolyte vs. ether-based electrolyte

Cation-disordered rock-salts (DRX) emerge as an intriguing class of high-capacity cathode materials, garnering significant attention in the development of advanced energy-storage systems. Fluorination strategies have been raised to regulate redox and structure for better DRX electrochemical performance. However, research on the interfacial processes during fluorinated DRX cycling remains limited. Here, we evaluate a highly fluorinated DRX, Li2Mn2/3Nb1/3O2F (LMNOF), in different electrolytes to correlate its cycling performance with distinct interfacial evolutions. During cycling in the carbonate-based electrolyte, a thick Mn-containing CEI forms on the LMNOF surface, leading to gradual capacity decay. Intriguingly, the addition of fluoroethylene carbonate (FEC) would bring about surface oxygen loss, Mn-ion dissolution and formation of a fluorinated surface layer by reacting with the LMNOF surface, which critically deteriorate the cycling performance. In comparison, the ether-based electrolyte is compatible with the LMNOF surface, resulting in a more favorable cycling stability. This work sheds light on the interfacial deterioration mechanism of LMNOF cathode in traditional carbonate-based electrolyte, emphasizing the importance of using advanced non-reactive electrolytes to enhance DRX performance.

Unlocking fast Li-ion transport in micrometer-sized Mn-based cation-disordered rocksalt cathodes

The development of cation-disordered rocksalt (DRX) cathodes has garnered worldwide attention due to their high capacity, broad chemical space and excellent structural flexibility. However, their low intrinsic Li-ion conductivity necessitates extensive particle pulverization, typically achieved through ball-milling process, which impedes large-scale production. In this work, we present a proton-exchange assisted strategy to activate the Li-ion transport in Mn-based DRX cathodes. Short-range spinel-like ordering is observed to form within the DRX matrix after the post treatment, which significantly enhances the intrinsic Li ion mobility. Notably, more than 280 mAh g−1 discharge capacity can be delivered at a slow rate from micrometer-sized particles with an overall disordered cation arrangement, which retains more than 150 mAh g−1 when cycled at a very high rate of 2000 mA g−1. Furthermore, we also demonstrate that the electrochemical performance of the post-treated cathodes can be further optimized by fine-tuning the reaction parameters.

Is There Hope for Ni-Based Disordered Rock Salt Cathode Materials?

Li-ion batteries achieved in the last 3 decades extremely high energy densities, making them the energy storage devices of choice for the electrification of our society. Despite this improvement, their energy density is still low as compared to gasoline, motivating further research towards materials with better performances. State of the art positive electrodes are nowadays layered materials with a ratio Li:M of 1:1, with M being one or multiple transition metals. LiNiO2 is a noteworthy example. Disordered rock salt (DRX) materials were instead thought to be electrochemically inactive until the development of a percolation theory,1 which demonstrated that lithium-rich materials (Li:M>1.1) with a cation disordered rock-salt structure (DRX) can achieve high reversible specific capacities. The general formula of these lithium-rich compounds can be written as Li1+y(MM′)1−yO2 where the Li content ranges usually from 1.05 to 1.33. With M is indicated a redox active specie (Mn, Ni, Fe, Cr, V) and M’ is typically a d0 element, which is redox inactive during charge and discharge and well accommodates the disordered structure.2 Materials with such structures have been shown to deliver extremely high specific capacities, resulting in equally high specific energies.3 In our recent work we investigated two DRX compounds based on Ni-redox. First, Li2NiO3, which is layered (with monoclinic distortion), but that decomposes to a disordered rock salt structure with cycling. The material displays interesting defect chemistry but fast capacity fading.4 More recently, we developed a class of Li-rich compounds with the chemical composition Li2yNiyTi2-3yO2 (y = 0.50, 0.55, 0.60, 0.67). These samples were prepared via solid-state reaction at three different temperatures (700 °C, 800 °C, 900 °C). By X-ray and neutron diffraction, we demonstrated a pure phase solid solution at high temperature, yet, by decreasing the synthesis temperature and increasing the Li content, phase separation occurs into a rock salt-type and a Li2TiO3 phase. The synthesis process has been also verified by DFT and by in situ X-ray diffraction. In all DRX materials synthesized, the electrochemical performances revealed a strong voltage hysteresis between charge and discharge and fast capacity fade.5,6 This raises then the question of whether any Ni-based DRX material can provide high capacity, high rate capability and stability, while avoiding the commonly encountered large hysteresis, or whether this can only be achieved in Mn-based compounds. In this presentation, by discussing our own work and recent literature reports, we aim at answering this question. Bibliography Urban, Alexander, Jinhyuk Lee, and Gerbrand Ceder. “The Configurational Space of Rocksalt-Type Oxides for High-Capacity Lithium Battery Electrodes.” Advanced Energy Materials4, 13: 1400478.Chen, Dongchang, Juhyeon Ahn, and Guoying Chen. “An Overview of Cation-Disordered Lithium-Excess Rocksalt Cathodes.” ACS Energy Letters, 2021, 1358–76.Clément et al., Cation-disordered rocksalt transition metal oxides and oxyfluorides for high energy lithium-ion cathodes, Energy & Environmental Science, 2020, 13 (2), 345-373Bianchini et al., From LiNiO2 to Li2NiO3: Synthesis, Structures and Electrochemical Mechanisms in Li-Rich Nickel Oxides, Chem. Mater. 2020, 32, 9211−9227Reitano, et al. Manuscript submitted, 2024.Li, Biao, Khagesh Kumar, Indrani Roy, Anatolii V. Morozov, Olga V. Emelyanova, Leiting Zhang, Tuncay Koç, et al. “Capturing Dynamic Ligand-to-Metal Charge Transfer with a Long-Lived Cationic Intermediate for Anionic Redox.” Nature Materials21, 10: 1165–74.

A Novel Approach to Continuous and Scalable Synthesis of Cation-Disordered Rocksalt Cathodes

Cation disordered rocksalts (DRX) are an emerging class of high energy density LIB cathodes that can utilize earth-abundant and low-cost redox active transition metals. The DRX cathodes can be synthesized through a rich chemistry of transition metals, where commonly, metal-oxide precursors are combined with lithium source via ball-milling and calcined to achieve cation disordered phase. In this work, we present a new alternative synthesis method to the traditional solid-state synthesis, which provides scalable and continuous production of cathode precursors. A soft synthesis method in aqueous media was adopted to produce Mn-rich cathode precursors in large scale, through which homogenous mixing of the introduced transition metal cations was achieved. Here we report the electrochemical and structural properties of as-synthesized DRX cathodes with various Mn-compositions.

Enhanced Electrochemical Performance of Disordered Rocksalt Cathode in a Localized High Concentration Electrolyte

Lithium (Li) transition metal oxides with layered structure, commonly employed as cathodes in Li-ion batteries, exhibit limited capacity, and employ less abundant and costly materials, raising sustainability concerns amid surging battery demand. Addressing this, lithium rich cation disordered rock salt cathode (DRX) materials have garnered substantial attention as they offer high capacity and cost benefits. Manganese (Mn) based DRXs, in particular, show promise due to the utilization of earth abundant materials and good thermal stability of Mn. However, these cathodes often face challenges when cycled in state-of-the-art carbonate-based electrolytes. These include severe side reactions between the cathode and the electrolyte, transition metal dissolution and structural instability of the cathode particles all of which result in fast capacity fading. In this work, an advanced localized high concentration electrolyte (LHCE) is developed to mitigate these problems and enable stable cycling of Li1.2Mn0.6Ti0.2O2 (LMTO). The developed LHCE exhibits high voltage stability, forming an ultrathin and stable electrode/electrolyte interphase. Consequently, Li||LMTO half cells with the developed LHCE demonstrate increased capacity, enhanced cycling stability and superior rate capabilities compared to the cells with the conventional electrolyte. For instance, the Li||LMTO cells cycled in LHCE show higher initial capacity of 205.2 mAh/g, and a capacity retention of 72.5 % in contrast to an initial capacity of 187.7 mAh/g and a capacity retention of 19.9 % observed in Li||LMTO cells with the conventional electrolyte after 200 cycles at a current density of 20 mA/g. This work paves the way for the development of practical DRX cathode- based high-energy Li batteries.

Rapid in-Situ Electrochemical Formation of Partially Disordered Spinel from Mn-Rich Disordered Rocksalt Cathodes

We present the development of an electrochemical formation method that enables rapid and in-situ formation of a partially disordered spinel phase from an initially disordered rocksalt (DRX) cathode. Recent studies on Mn-rich DRX materials have demonstrated the emergence of a spinel-like phase during cycling, resulting in improved capacity retention, energy density, and rate capability compared to materials which do not transform1,2,3. However, this transformation process typically requires weeks of cycling at relatively low rates, posing significant challenges for the commercialization of such materials.To gain a deeper understanding of this transformation process, we carry-out a systematic study to determine whether the formation process of these spinel-like materials can be accelerated through a precycling formation process. By employing a novel electrochemical approach to purposefully stimulate the transformation, we successfully reduce the time required from several weeks to as little as one day for Mn-rich DRX. Extended cycling and synchrotron X-ray diffraction confirm that these materials exhibit both equivalent performance and resulting structure to those obtained through conventional cycling over a much longer duration. Further characterization of this material using HAADF and 4-D STEM reveals the complex local structure of the spinel-like partial ordering. It is hoped that such a practical electrochemical formation method will allow for an acceleration of research on these earth-abundant and energy-dense materials. Li, L.; Lun, Z.; Chen, D.; Yue, Y.; Tong, W.; Chen, G.; Ceder, G.; Wang, C. Fluorination-Enhanced Surface Stability of Cation-Disordered Rocksalt Cathodes for Li-Ion Batteries. Adv Funct Mater 2021, 31 (25), 2101888. https://doi.org/10.1002/adfm.202101888.Ahn, J.; Giovine, R.; Wu, V. C.; Koirala, K. P.; Wang, C.; Clément, R. J.; Chen, G. Ultrahigh-Capacity Rocksalt Cathodes Enabled by Cycling-Activated Structural Changes. Adv. Energy Mater. 2023. https://doi.org/10.1002/aenm.202300221. Cai, Z.; Ouyang, B.; Hau, H.-M.; Chen, T.; Giovine, R.; Koirala, K. P.; Li, L.; Ji, H.; Ha, Y.; Sun, Y.; Huang, J.; Chen, Y.; Wu, V.; Yang, W.; Wang, C.; Clément, R. J.; Lun, Z.; Ceder, G. In Situ Formed Partially Disordered Phases as Earth-Abundant Mn-Rich Cathode Materials. Nat. Energy 2023, 1–10. https://doi.org/10.1038/s41560-023-01375-9.

Chemical Origin of in Situ Carbon Dioxide Outgassing from a Cation-Disordered Rock Salt Cathode.

In situ carbon dioxide (CO2) outgassing is a common phenomenon in lithium-ion batteries (LiBs), primarily due to parasitic side reactions at the cathode-electrolyte interface. However, little is known about the chemical origins of the in situ CO2 released from emerging Li-excess cation-disordered rock salt (DRX) cathodes. In this study, we selectively labeled various carbon sources with 13C in cathodes containing a representative DRX material, Li1.2Mn0.4Ti0.4O2 (LMTO), and performed differential electrochemical mass spectrometry (DEMS) during galvanostatic cycling in a carbonate-based electrolyte. When charging LMTO cathodes, electrolyte solvent (EC) decomposition is the dominant source of the CO2 outgassing. The amount of EC-originated CO2 is strongly correlated with the total surface area of carbon black in the electrode, revealing the critical role of electron-conducting carbon additives in the electrolyte degradation mechanisms. In addition, unusual bimodal CO2 evolution during the first cycle is found to originate from carbon black oxidation. Overall, the underlying chemical origin of in situ CO2 release during battery cycling is highly voltage- and cycle-dependent. This work further provides insights into improving the stability of DRX cathodes in LiBs and is envisioned to help guide future relevant material design to mitigate parasitic reactions in DRX-based batteries.

Enhanced Electrochemical Performance of Disordered Rocksalt Cathodes in a Localized High‐Concentration Electrolyte

Enhanced Electrochemical Performance of Disordered Rocksalt Cathodes in a Localized High‐Concentration Electrolyte