Transition Metal Oxide Cathode Research Articles

Buckled-layer K1.39Mn3O6: a novel cathode for potassium-ion batteries.

A novel buckled-layer K1.39Mn3O6 cathode was synthesized, featuring P2-oxygen stacking and P3-K sites. The presence of two independent manganese sites significantly influences the charge distribution and diffusion pathways of potassium ions during the charge and discharge processes, resulting in exceptional electrochemical performance. A reversible capacity of 105 mA h g-1 at 100 mA g-1 and remarkable rate capability of 70 mA h g-1 at 1 A g-1 were achieved, surpassing those of most previously reported layered transition metal oxide cathodes. The findings facilitate the development of innovative cathode materials.

Interface Issues of Layered Transition Metal Oxide Cathodes for Sodium-Ion Batteries: Current Status, Recent Advances, Strategies, and Prospects.

Sodium-ion batteries (SIBs) hold significant promise in energy storage devices due to their low cost and abundant resources. Layered transition metal oxide cathodes (NaxTMO2, TM = Ni, Mn, Fe, etc.), owing to their high theoretical capacities and straightforward synthesis procedures, are emerging as the most promising cathode materials for SIBs. However, the practical application of the NaxTMO2 cathode is hindered by an unstable interface, causing rapid capacity decay. This work reviewed the critical factors affecting the interfacial stability and degradation mechanisms of NaxTMO2, including air sensitivity and the migration and dissolution of TM ions, which are compounded by the loss of lattice oxygen. Furthermore, the mainstream interface modification approaches for improving electrochemical performance are summarized, including element doping, surface engineering, electrolyte optimization, and so on. Finally, the future developmental directions of these layered NaxTMO2 cathodes are concluded. This review is meant to shed light on the design of superior cathodes for high-performance SIBs.

Electrolyte Design to Improve Solid Electrolyte Interphase for Sodium-Ion Batteries

Hard carbon (HC) is a suitable anode for sodium-ion batteries. However, its initial coulombic efficiency is a major drawback resulting in cell energy density loss. This issue can be tackled by designing electrolyte combinations. Increasing the salt concentrations can help the formation of a robust and well-balanced organic-inorganic electrolyte interface layer.1 Anion-derived SEI layer is developed on the electrode surface due to a change of salt concentration to a higher limit.2 The solvation structure of electrolytes also plays a vital role in SEI layer building.3 Commercial hard carbon is studied using the most common solvents, such as ethylene carbonate (EC) and propylene carbonate (PC), in the ratio of 1:1 v/v. NaClO4 and NaFSI salts are used in different concentrations. Our baseline electrolyte is 1M NaClO4 in EC: PC (1:1 v/v) which provides a capacity of 326 mAh g-1 with an ICE value of 63.3% at 0.1C rate (Fig 1a). Changing salt anion from ClO4 - to FSI- does not help improve capacity or coulombic efficiency. However, if we optimized the concentration to 3M, then the capacity would be 356 mAh g-1 with an ICE value of 73% (Fig 1b). This difference in ICE is due to stable anion-derived SEI layer formation. The oral presentation will focus on the effect of salt concentration on the battery performance of Commercial HC and Transition Metal Oxide cathode in half-cell and full-cell configurations in Na-ion batteries. Reference Y. Yamada, J. Wang, S. Ko, E. Watanabe, and A. Yamada, Nat. Energy, 4, 269–280 (2019).J. Patra et al., Energy Storage Mater., 16, 146–154 (2019).Y. Ugata et al., Phys. Chem. Chem. Phys., 23, 21419–21436 (2021).

Understanding Degradation Mechanisms of Layered Transition Metal Oxide Cathodes through Multiscale Characterization

Co has been extensively used in lithium-ion battery (LIB) cathodes with LiTMO2 structure (TM: transition metals) due to its high specific capacity and stability. However, the scarcity and costliness of Co have prompted researchers to explore alternatives utilizing more abundant and cost-effective elements like Mn and Ni. Despite these efforts towards Co reduction or elimination, there remains a critical knowledge gap concerning the specific functions of cobalt in cathode capacity and structural stability. In this study, we employed advanced characterization techniques including transmission electron microscopy (TEM) and X-ray diffraction (XRD) to investigate the roles of cobalt in Co-free Ni-rich cathodes, as well as to elucidate degradation mechanisms in Li- and Mn-rich cathodes.To understand the Co roles, Co-rich LiNi0.6Co0.4O2, (NC64) and Mn-substituted Co-free LiNi0.6Mn0.4O2 (NM64) were used [1]. TEM observations show that both NC64 and NM64 surface structures change to a rock-salt phase after prolonged cycling, suggesting surface phase transformation was independent of the Co and Mn content. However, the surface structures for NC64 and NM64 during the cycling exhibit clear difference. The subsurface structure of NC64 completely transited to a Co3O4-type spinel-like structure. Such an irreversible phase transition is related to oxygen release, which triggers TM migration to form a spinel-like phase. In contrast, the structure stability of NM64 remained a typical layered structure after 100 cycles, indicating the Co reduction and Mn substitution improved the stability of the structure and oxygen of Ni-rich cathodes. Electron energy-loss spectroscopy (EELS) line scans from surface to subsurface of NM64 sample shows the O K-edge pre-peak only decreased near the surface, and the L edges of Ni and Mn also consistently shift towards lower energy loss near the surface. These results suggest that oxygen release only occurred on surface areas of the NM64 particles. In contrast, oxygen released not only occurred on the surface, but also extended into bulk NC64, because the O K-edge pre-peak of NC64 exhibited a relatively low intensity in the whole scan area of around 40 nm. In conclusion, Co is detrimental to structural/ morphological stability and oxygen reversibility. Co reduction and Mn increase could greatly alleviate these challenges in Ni-rich cathodes.HRTEM observations indicate that Li- and Mn-rich cathodes consist of nanoscale Li2MnO3 and layered domains. To understand the voltage fade mechanism in Li- and Mn-rich cathodes [2], XRD, TEM, 3D rotation electron diffraction (3D-rED), and EELS were performed on delithiated samples to investigate lattice displacement and nanostructure evolution. XRD and TEM studies show that inhomogeneous electrochemical activities and structural difference between Li2MnO3 and layered domains result in nanoscale strain. The accumulated strain severely affects the structural stability of the composite Li- and Mn-rich cathode, which triggers the decomposition of Li2MnO3 domains, oxygen release and TM migration. The activation of Li2MnO3 and oxygen release in turn release the lattice strain at high voltages.

Tailoring Surface Oxygen Environments in LiNi0.5Mn0.3Co0.2O2 Via Post-Calcination Anneal

Oxygen release in layered transition metal oxide cathodes leads to changing intercalation kinetics in lithium-ion batteries. Oxygen loss behavior during extended electrochemical cycling is well understood, but tailoring the oxygen environment of pristine cathode materials to reduce oxygen release remains a challenge. In this work we perform simple 30-minute post-calcination gas treatments to systematically modify the surface of single-crystalline LiNi0.5Mn0.3Co0.2O2 (NMC532). We use two gas environments (Ar and 21% O2 in Ar) and a range of temperatures (600-800 °C) to investigate the effect of low oxygen partial pressure on pristine NMC532. Using electrochemical and X-ray techniques, we observe changes in electrochemical cycling behavior and surface and bulk structure that are monotonic with temperature for the argon annealed material, while changes in the oxygen annealed material are mostly invariant with respect to temperature. From in situ heating X-ray photoelectron spectroscopy and in situ heating X-ray absorption spectroscopy, we demonstrate the removal of surface carbon species and oxidation of transition metals in an oxygen containing environment; in an argon environment we observe transition metal reduction, consistent with oxygen release. These findings suggest 1) a simple oxygen environment anneal can remove resistive surface contaminants commonly formed during material storage, and 2) oxygen-deficient anneals can be used to systematically alter the surface oxygen environments of stoichiometric cathode materials. This can be a powerful method to understand the relationship between the surface oxygen sublattice and the kinetics of lithium intercalation.

Tailoring Cathode Materials: Al2O3 Coating for Advanced Sodium-Ion Batteries

The attractive combination of sodium-ion battery's (SIB) homogeneous profusion in earth and LIB's identical intercalation chemistry makes it possible drop-in replacement for lithium-ion battery (LIB) technology in the ever-growing energy storage market. Layered transition metal oxide cathodes are the most sought-after for SIB cathodes because of their superior sodium storage capabilities, increased energy density, and straightforward synthesis process. However, these intercalation materials are prone to severe capacity decline and pose several safety concerns. In addition to safety concerns, several explanations of this capacity fading have been proposed, including structural instability, metal ion solubility in the electrolyte due to HF generation, and degradation of the electrolyte at higher cutoff voltages (>4.3 V). Metal oxide coatings are viable owing to their cost-effectiveness and ease of application. The inactivity of the metal during electrochemical reactions is attributed to its persistent valance state; consequently, cathodes adorned with such coatings experience a decline in ion conductivity. In this research, a thin layer of coating is employed upon titanium and vanadium doped sodium iron manganese oxide () via sol-gel process followed by a solid-state ball milling method in order to improve the rate capability and long term cyclic stability. The thickness and uniformity of the coating layer is verified from the SEM and EDS images. Furthermore, the XRD analysis is performed to see whether any modification has occurred in the cathode lattice due to the coating. Following that, the electrochemical performance of uncoated P2-electrodes is compared to that of coated P2- electrodes via electrochemical analyses such as galvanostatic charge-discharge test, CV and EIS which validate the efficacy of coating on ). This straightforward surface modulation technique will open up a potential route for the synthesis of superior cathode materials for sodium-ion batteries.

Amorphization Progress of Microscale-Silicon Studied via Operando and in Situ X-Ray Diffraction during Formation and Cycling

Silicon as an anode active material for lithium-ion batteries has a theoretical gravimetric capacity of 3579 mAh g-1, considering the highest electrochemically lithiated phase of Li3.75Si.1 Hence, silicon has gained increasing interest in the last years to either partially or completely replace graphite in commercial lithium-ion batteries to increase energy density.2 However, the expansion of silicon of up to 300% upon complete lithiation bears challenges such as particle cracking, loss of electrical contact to the active material, and the continuous formation of the solid-electrolyte interphase (SEI). To decrease these detrimental effects, partial lithiation of microscale silicon was introduced, limiting the used capacity of silicon to ~1200 mAh g-1 and thus reducing its overall expansion, rendering ~250 cycles in full-cells possible.3 XRD measurements during the initial lithiation of crystalline silicon revealed that it is irreversibly amorphized in the first cycle when its potential drops below ~170 mV vs. Li+/Li.4 In the case of partial lithiation of microscale silicon, cycling above this potential limit leads to amorphized silicon particles with a remaining crystalline fraction. In this state, the amorphized part forms a lower lithiated phase LixSi (with x~2), which can be reversibly de-/lithiated.5 In this study, the amorphization progress of microscale silicon full-cells using a single-layer pouch cell setupwas investigated operando over the first four formation cycles and in situ after extended cycling. The anodes consisted of 70% silicon (d 50 =4.5 µm, Wacker Chemie AG), 8% LiPAA binder (Sigma Aldrich), 2% conductive carbon (Super C65, Imerys), and 8% graphite (KS6L, Imerys). The cathode consisted of a nickel-rich transition metal oxide cathode active material (LiNi0.83Co0.12Mn0.05O2, BASF SE). As electrolyte, a 1 M LiPF6 in FEC:DEC 2:8 (v:v) was used. As shown in Figure 1, the cycling performance in pouch cells, reaching 80% state-of-health (SOH) after ~250 cycles at 25 °C matches well with the literature.6 Figure 1 highlights the cycles at or after which XRD measurements were performed. To accomplish operando XRD measurements, a custom-made pouch cell holder with glassy carbon windows was used, which allows for an operating compression of 2 bar. In this setup, an XRD pattern could be taken every ~15 min for the first four cycles at 0.1 h-1. Using the XRD analysis method developed previously,5 the XRD data confirm a significant amorphization in the first charge, while no amorphization occurs during the relaxation phase and during discharge of the cell. In the second charge, the amorphization continues only after ~70% of the capacity was transferred. The start of amorphization aligns with the anode onset potential of ~170 mV vs. Li+/Li, in accordance with the literature.4,5 With increasing cycling number, the progress of amorphization per cycle decreases. Although only ~33% of the silicon capacity (i.e., 1200 mAh/g) is reversibly used, the amorphization reaches ~70% after 50 cycles, highlighting the significant particle usage. Continuous cycling up to 500 cycles leads to no significant further amorphization of the silicon.

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.

Mitigating Capacity Degradation and Surface Oxygen Loss of Single-Crystalline LiNiO2 Cathodes Via Al2O3 Surface Coating

The performance of next-generation Li-ion batteries (LIBs) for electric vehicle applications relies on energy-dense and low-cost lithium-ion chemistries. Single-crystalline LiNiO2 (SC-LNO) cathodes are regarded as promising materials for high-energy-density applications owing to their high practical capacity, resistance to particle cracking and competitive cost [1]. However, under high voltage operation (≥ 4.4 vs. graphite), they experience rapid capacity loss, owing to parasitic electrode-electrolyte reactions expedited by surface oxygen loss [2]. Overcoming this, stabilising the long-duration performance of SC-LNO cathodes to operate at high voltages while maintaining capacity retention is critical for their integration into commercial batteries. Surface engineering by coating could provide an effective approach to tune the electrochemistry of Ni-rich cathodes while inhibiting degradation pathways [3,4]. Aluminium oxide (Al2O3) coating is used as a barrier to eliminate highly reactive electrolyte species (HF) from the cathode surface, thereby enhancing long-term stability and improving high voltage performance [5,6]. It offers a viable strategy to control the surface of SC-LNO from O loss (O-n, n > 2) and protect it from electrolyte attack. In this study, we employ an ultrathin and conformal film of AlOx on SC-LNO powder via Powder Atomic Layer Deposition (P-ALD). To minimise moisture exposure, the slurry and casting processes were performed in a controlled dry room environment. Electrochemical testing was carried out in balanced coin cells (vs. commercial graphite) at 25 oC and cycled between a voltage range of 2.5–4.2 V and 2.5–4.4 V. Following two formation cycles performed at a C/20 rate, the cells were cycled 100 times at C/3 rate. Electrochemical impedance spectroscopy measurements were also performed before and after 100 cycles to assess any impedance changes.The electrochemical data revealed that AlOx coated SC-LNO cathodes provide significantly higher capacity retention (94.5%) than uncoated ones (66.3%) after 50 cycles at 4.4 V (vs. graphite). Regarding the rate capability test, the coated cathode delivers improved and stable capacities at faster rates compared with uncoated SC-LNO cathodes. Online electrochemical mass spectroscopy (OEMS) analysis of the AlOx coated cathodes indicates that the onset potential for oxygen loss related gas evolution is > 4.4 V vs. Li/Li+. In contrast, for the uncoated SC-LNO sample, this was found to be ~4.2 V. Hence, the AlOx coating serves as a protective layer, for the cathode against electrolyte-induced degradation and transition metal dissolution at high voltage by forming Al-O-F species at the surface [6]. This beneficial interaction enhances the electrochemical performance by effectively inhibiting impedance growth and improving the cycling life and stability of SC-LNO cathodes. This study highlights the crucial role of AlOx coatings in mitigating surface oxygen loss, which is a key factor contributing to the deterioration of cell performance and issues related to Li+ kinetics. Our findings significantly contribute to advancing the development of high-performance SC-LNO cathode materials, offering valuable insights into the application of ALD coatings for enhancing the performance of Li-ion battery cells.[1]. Lee, Dong-hee, Maxim Avdeev, Dong-il Kim, Weon Ho Shin, John Hong, and Minkyung Kim. "Regulating Single-Crystal LiNiO2 Size and Surface Coating toward a High-Capacity Cathode for Lithium-Ion Batteries." ACS Applied Energy Materials 6, no. 10 (2023): 5309-5317.[2]. Zhang, Hanlei, Hao Liu, Louis FJ Piper, M. Stanley Whittingham, and Guangwen Zhou. "Oxygen loss in layered oxide cathodes for Li-ion batteries: Mechanisms, effects, and mitigation." Chemical reviews 122, no. 6 (2022): 5641-5681.[3]. Shi, Yang, Yingjie Xing, Kitae Kim, Taehwan Yu, Albert L. Lipson, Arrelaine Dameron, and Justin G. Connell. "Communication—reduction of DC resistance of Ni-rich lithium transition metal oxide cathode by atomic layer deposition." Journal of the Electrochemical Society 168, no. 4 (2021): 040501.[4]. Haworth, Abby R., Beth IJ Johnston, Laura Wheatcroft, Sarah L. McKinney, Nuria Tapia-Ruiz, Sam G. Booth, Alisyn J. Nedoma, Serena A. Cussen, and John M. Griffin. "Structural Insight into Protective Alumina Coatings for Layered Li-Ion Cathode Materials by Solid-State NMR Spectroscopy." ACS Applied Materials & Interfaces (2024).[5]. Chen, Zonghai, Yan Qin, Khalil Amine, and Y-K. Sun. "Role of surface coating on cathode materials for lithium-ion batteries." Journal of materials chemistry 20, no. 36 (2010): 7606-7612.[6]. Lebens-Higgins, Zachary W., David M. Halat, Nicholas V. Faenza, Matthew J. Wahila, Manfred Mascheck, Tomas Wiell, Susanna K. Eriksson et al. "Surface Chemistry Dependence on Aluminum Doping in Ni-rich LiNi0. 8Co0. 2− y Al y O2 Cathodes." Scientific reports 9, no. 1 (2019): 17720. Figure 1

A Machine Learning Approach for Understanding the Oxygen Vacancy Formation Energies within DRX Cathode Structures

Disordered Rock-Salt (DRX) cathode structures are materials where lithium and transition metal atoms are arranged in a disordered solid solution. These structures are currently under intensive study [1] due to their potential higher energy density, bigger capacity than the typical layered cathode structure, and improved flexibility in the selection of raw materials. Driven by this, we have recently compiled a DFT-based database of DRX structures with over 6,000 different metal oxide compositions. Moreover, since oxygen loss is linked to voltage degradation, intergranular cracks, and irreversible phase transformation, developing a descriptor that allows us to understand and reflect the stability of oxygen within the DRX anion lattice is crucial. It represents a significant research challenge that our study aims to address.In this work, we study two things: First, since the generation of oxygen vacancies holds a critical value in elucidating the stability of cathode material oxides[2], our methodology focuses on generating an extensive DFT database of over 1,400 oxygen vacancy formation energies (Evf(O)) from selected DRX structures. We then employ a machine learning (ML) model to predict the Evf(O) and their distribution for a variety of different compositions. The ML model incorporates site-specific features, such as the maximum reduction potential of the cations neighboring the O vacancy, the O p-band center of mass, and information from atomic population analysis (such as the bond order and the bond spin polarization between each O and its nearest neighbors). This approach is necessary because the DRX structure contains different local environments where O vacancies could be created, and recent work from Baldassarri et al. has highlighted the limitations of ML models that only include global features and lack their ability to differentiate the behavior of compounds containing the same elements but in different oxidation states [3]. This allows us to predict the O vacancies energetics with an accuracy comparable to DFT and to develop a descriptor to classify different compositions of DRX structures.Second, given that oxygen destabilizes during delithiation, we analyze the impact and relationship of the Li vacancy formation energies (Evf(Li)) and Evf(O) of each O able to create a vacancy. The results show a strong interaction between these energetics, and in particular, an inverse correlation between Evf(O) of a specific O site and the Evf(Li) of the Li atoms that surround this O, which within these DRX prototypes the number of surrounding Li varies from 1 to 5. In line with what others proposed [4], there is a strong interaction between these two vacancy types. However, we expect that the generation of O vacancies is determined not only by their thermodynamic driving force but also by the displacement/migration of the nearest neighbor lithium (NN-Li) that surrounds each O.The methodology and fundamental understanding developed in this study about DRX O-vacancies and their relationship with NN-Li during delithiation could help investigate and describe compositionally similar transition metal oxide cathodes belonging to the same crystal structure family (layered, spinel-like, γ-LiFeO2). Hence, this research not only enhances our understanding of these materials but also paves the way for the design and development of more flexible and stable energy storage systems.[1] S. Anand, B. Ouyang, T. Chen, G. Ceder, Impact of the energy landscape on the ionic transport of disordered rocksalt cathodes, Physical Review Materials 7(9) (2023) 095801.[2] H. Zhang, B.M. May, F. Omenya, M.S. Whittingham, J. Cabana, G. Zhou, Layered Oxide Cathodes for Li-Ion Batteries: Oxygen Loss and Vacancy Evolution, Chemistry of Materials 31(18) (2019) 7790-7798.[3] B. Baldassarri, J. He, A. Gopakumar, S. Griesemer, A.J.A. Salgado-Casanova, T.-C. Liu, S.B. Torrisi, C. Wolverton, Oxygen Vacancy Formation Energy in Metal Oxides: High-Throughput Computational Studies and Machine-Learning Predictions, Chemistry of Materials 35(24) (2023) 10619-10634.[4] C. James, Y. Wu, B.W. Sheldon, Y. Qi, The impact of oxygen vacancies on lithium vacancy formation and diffusion in Li2-xMnO3-δ, Solid State Ionics 289 (2016) 87-94.

Determining Electrode Microstructural Parameters with X-Ray Microscopy

The transportation industry is in the midst of a transition to electric vehicles (EVs). In order to drive the mass adoption of EVs by consumers, technology advancements are needed. Significant barriers to vehicle performance stem from limitations in battery cell electrochemistry. In particular, a lack of understanding of electrode-level volume change during battery charging/discharging contributes to unclear design parameters at the battery pack level. In this work, we present a methodology to quantify electrode-level thickness changes during cycling using X-ray imaging, a non-destructive technique. This approach provides the ability to track thickness change during cycling without sacrificing the cell. Additionally, we show a method to compute porosities and tortuosities of layered transition metal oxide cathode materials with high-resolution X-ray imaging. These parameters are key inputs to physics-based models employing porous electrode theory. In sum, this work can be used to optimize pack design and to speed up virtualization efforts to more rapidly screen promising cell chemistries for future vehicle technologies.

Developing Aqueous Processed Transition Metal Oxide Cathodes with Sustainable Binders for High Energy Density Lithium-Ion Batteries from Lab Scale to Manufacturing Scale

Transitioning toward more sustainable materials and manufacturing methods is critical to continue supporting the rapidly expanding market for lithium-ion batteries (LIBs). Meanwhile, energy storage applications are requiring higher power and energy densities with demanding performance targets like fast charging and a wide range of operating voltages. Alongside high-performance demands, environmental considerations such as organic solvent use, low abundance of Co and other mining related issues, urgently need to be addressed by the LIBs community [1]. High voltage spinel LiNi0.5Mn1.5O4 (LNMO) is considered a highly promising cathode candidate for the next generation high performance LIBs due to a high energy density (650 W H kg -1), high operating voltage (∼4.7 V vs Li), low environmental impact, and low-cost fabrication [2]. However, severe capacity degradation during cycling has impeded wide application and commercialization.In this study, we investigated LNMO thoroughly as a cathode material using only aqueous processing, covering the processing range from small scale to the research pilot line level. Aqueous electrode processing is highly critical to eliminate organic solvent use in LIBs production. On the anode side, aqueous processing has already been established on the industrial level, whilst cathode aqueous processing still needs to be tuned to reach to the same level of feasibility. The main challenge in aqueous processing of transition metal oxides is the high surface sensitivity towards water, resulting in Li/proton exchange. Consequently, pronounced Li+ loss is observed on the electrode during cycling. In literature, acid treatment is one of the most common approaches to avoid this phenomenon during slurry preparation [3]. In this work, we investigate different crystal structure with combination of two binders. Understanding the impact of the different crystal structure of LNMO particles on lithium leaching during slurry processing is one the targets of the study. On the particle level, single, poly crystalline and mixed of single and poly crystal powders are characterized to select the most promising candidate in terms of processing and cycling performance. Two different binder systems were studied, including carboxymethyl cellulose (CMC) with acrylic based binder as baseline for water-borne cathodes, and Na-Alginate as a more sustainable binder option specifically for LNMO.The formulation development started at the laboratory scale with slurries characterized with pH control and regarding their rheological behavior. Detailed electrochemical analysis with cycling and electrochemical impedance spectroscopy (EIS) was performed along with comprehensive surface characterization and scanning electron microscopy (SEM) before cycling and post-mortem. Subsequently, the most promising candidates were successfully upscaled to the research pilot line. By characterizing three crystal structures of LNMO with two binders, we demonstrate the capabilities of LNMO as an active material using the most sustainable processing conditions. Depending on the crystal structure, single crystal LNMO with Na-Alginate binder was found to be the most promising candidate (capacity retention ∼130 mAh g -1 after 150 cycles), especially for fast charging applications. This study is to serve as guideline for better understanding of LNMO and its aqueous processability.

Quasi-Solid-State Conversion with Fast Redox Kinetics Enabled by a Sulfonamide-Based Electrolyte in Li-Organic Batteries.

The serious dissolution of organic electrode materials (e.g., perylene-3,4,9,10-tetracarboxylic dianhydride, PTCDA) in electrolytes is a major challenge, deteriorating their electrochemical performances and hindering the interpretation of the fundamental redox reaction mechanisms including the intrinsic kinetics and the solvent cointercalation. To address these issues, we propose a rationally designed sulfonamide-based electrolyte to enable a quasi-solid-state conversion (QSSC) of the PTCDA cathode by effectively suppressing its dissolution in the electrolyte. Benefiting from the QSSC, the Li||PTCDA cells can retain ∼95.8% of the original capacity after 300 cycles with both high and stable energy efficiencies >95%, even comparable to the layered transition-metal oxide cathodes, greatly outperforming an ether-based electrolyte with a high PTCDA solubility. The high energy efficiencies indicate that the QSSC of PTCDA has intrinsic fast redox kinetics. Furthermore, the solvent cointercalation mechanism was investigated by density functional theory/molecular dynamic calculations. This work develops a strategy for designing electrolytes for highly stable and efficient Li-organic batteries.

Progress and Perspective of High‐Entropy Strategy Applied in Layered Transition Metal Oxide Cathode Materials for High‐Energy and Long Cycle Life Sodium‐Ion Batteries

AbstractLayered transition metal oxide (LTMO) cathode materials of sodium‐ion batteries (SIBs) have shown great potential in large‐scale energy storage applications owing to their distinctive periodic layered structure and 2D ion diffusion channels. However, several challenges have hindered their widespread application, including phase transition complexities, interface instability, and susceptibility to air exposure. Fortunately, an impactful solution has emerged in the form of a high‐entropy doping strategy employed in energy storage research. Through the implementation of high‐entropy doping, LTMOs can overcome the aforementioned limitations, thereby elevating LTMO materials to a highly competitive and attractive option for next‐generation cathodes of SIBs. Thus, a comprehensive overview of the origins, definition, and characteristics of high‐entropy doping is provided. Additionally, the challenges associated with LTMOs in SIBs are explored, and discussed various modification methods to address these challenges. This review places significant emphasis on conducting a thorough analysis of the research advancements about high‐entropy LTMOs utilized in SIBs. Furthermore, a meticulous assessment of the future development trajectory is undertaken, heralding valuable research insights for the design and synthesis of advanced energy storage materials.

The Role and Substitution of Cobalt in the Cobalt‐Lean/Free Nickel‐Based Layered Transition Metal Oxides for Lithium Ion Batteries

AbstractThe Nickel‐based layered transition metal oxide cathode represented by NCM (LiNixCoyMnzO2, x+y+z=1) and NCA (LiNixCoyAlzO2, x+y+z=1) is widely used in the electric vehicle market due to its specific capacity and high working potential, in which Cobalt (Co) plays a huge role in improving the structural stability during the cycle. However, the limited supply of Co, due to its scarcity and the influence of geopolitics, poses a significant constraint on the further advancement of the Nickel‐based layered transition metal oxide cathode in the field of energy storage. In this paper, the mechanism of Co in the Nickel‐based layered transition metal oxides is reviewed, including its critical role for structural stability such as the inhibition of cationic mixing and the release of lattice oxygen et al. Subsequently, it outlines various strategies to enhance the performance of Co‐lean/free materials, such as ion doping, including single‐ion doping and multi‐ion co‐doping, and various surface coating strategies, so as to eliminate the adverse effects of Co loss on materials. Ultimately, this paper offers a glimpse into the promising future of Cobalt‐free strategies for high performance of Nickel‐based layered transition metal oxides.

Investigation on the Necessity of Low Rates Activation toward Lithium‐Sulfur Batteries

AbstractLow rate activation process is always used in conventional transition metal oxide cathode and fully activates active substances/electrolyte to achieve stable electrochemical performance. However, the related working mechanism in lithium‐sulfur (Li‐ battery is unclear due to the multiple complex chemical reaction steps including the redox of sulfur and the dissolution of polysulfides intermediate. Hence, the influencing mechanism of activation process on Li‐S battery is explored by adopting different current densities of 0.05, 0.2, and 1 C in initial three cycles before long‐term cycling tests at 0.2 C (denoted by 0.05, 0.2, and 1‐battery). 0.05‐battery presents the highest initial capacity in activation process, while 0.2‐battery presents superior electrochemical performances after 150 cycles. The similar trend can be found in more long‐term cycling rates such as 0.02, 0.1, 0.5, and 1 C. Potentiostatically Li2S precipitation test demonstrates that rapid generation of Li2S is achieved at higher current density, and S8‐Li2Sn‐Li2S conversion is accelerated according to Tafel plots. However, interfacial electrochemical and physical characterizations suggest that serious lithium dendrite growth will be induced under high current density. Therefore, considering the reaction kinetics and interfacial properties, low rate activation process is unnecessary when cycling current lower than 1 C for Li‐S battery.

Chemo-mechanical instabilities in lithium cobalt oxide at higher state-of-charge in Li-Ion batteries

Transition metal oxide cathodes are widely used in commercial Li-ion batteries. However, their practical charge capacity is limited due to severe chemo-mechanical instabilities at higher charge voltage, and state-of-charge condition. Here, in situ stress and strain measurements were synchronized to probe mechanical deformations in the lithium cobalt oxide (LCO) cathode via a multi-beam stress sensor and digital image correlation, respectively. In situ mechanical measurements revealed how Li removal from the electrode structure induces deformations on the LCO composite cathodes during cycling. The structure and morphology of the LCO cathodes were further investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies. Two distinct electrochemical and mechanical behaviors were identified when the LCO was charged up to 4.65 V. The LCO undergoes a compressive stress generation when charged up to 4.2 V and surface fractures on the LCO particles were detected by SEM. LCO cathode experienced significantly large contractions (negative strains) when charged up to 4.65 V, where intergranular crack formation and phase transformation were detected on the LCO particles via SEM and XRD, respectively. Overall, the study bridges complicated structural deformations with in situ analysis of mechanical degradations in LCO cathodes charged at higher voltages. The correlation is vital to understanding instability mechanisms in transition metal oxides at high voltages for alkali metal ion batteries.

Roadmap for the Development of Transition Metal Oxide Cathodes for Rechargeable Zinc-Ion Batteries

Roadmap for the Development of Transition Metal Oxide Cathodes for Rechargeable Zinc-Ion Batteries

Solvent-mediated oxide hydrogenation in layered cathodes.

Self-discharge and chemically induced mechanical effects degrade calendar and cycle life in intercalation-based electrochromic and electrochemical energy storage devices. In rechargeable lithium-ion batteries, self-discharge in cathodes causes voltage and capacity loss over time. The prevailing self-discharge model centers on the diffusion of lithium ions from the electrolyte into the cathode. We demonstrate an alternative pathway, where hydrogenation of layered transition metal oxide cathodes induces self-discharge through hydrogen transfer from carbonate solvents to delithiated oxides. In self-discharged cathodes, we further observe opposing proton and lithium ion concentration gradients, which contribute to chemical and structural heterogeneities within delithiated cathodes, accelerating degradation. Hydrogenation occurring in delithiated cathodes may affect the chemo-mechanical coupling of layered cathodes as well as the calendar life of lithium-ion batteries.

Microstrain screening towards defect-less layered transition metal oxide cathodes.

Microstrain and the associated surface-to-bulk propagation of structural defects are known to be major roadblocks to developing high-energy and long-life batteries. However, the origin and effects of microstrain during the synthesis of battery materials remain largely unknown. Here we perform microstrain screening during real-time and realistic synthesis of sodium layered oxide cathodes. Evidence gathered from multiscale in situ synchrotron X-ray diffraction and microscopy characterization collectively reveals that the spatial distribution of transition metals within individual precursor particles strongly governs the nanoscale phase transformation, local charge heterogeneity and accumulation of microstrain during synthesis. This unexpected dominance of transition metals results in a counterintuitive outward propagation of defect nucleation and growth. These insights direct a more rational synthesis route to reduce the microstrain and crystallographic defects within the bulk lattice, leading to significantly improved structural stability. The present work on microstrain screening represents a critical step towards synthesis-by-design of defect-less battery materials.