Layered Oxide Cathode Materials Research Articles

High-Entropy Layered Oxide Cathode Materials with Moderated Interlayer Spacing and Enhanced Kinetics for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) with low cost and environmentally friendly features have recently attracted significant attention for renewable energy storage. Sodium layer oxides stand out as a type of promising cathode material for SIBs owing to their high capacity, good rate performance, and high compatibility for manufacturing. However, the poor cycling stability of layer oxide cathodes due to structure distortion greatly impacts their practical applications. Herein, a high entropy doped Cu, Fe, and Mn-based layered oxide (HE-CFMO), Na0.95Li0.05Mg0.05Cu0.20Fe0.22Mn0.35Ti0.13O2 for high-performance SIBs, is designed. The HE-CFMO cathode possesses high-entropy transition metal (TM) layers with a homogeneous stress distribution, providing a moderated interlayer spacing to maintain the structure stability and enhance Na+ ion diffusion. In addition, Li doping in TM layers increases the Mn valence state, which effectively suppresses John-Teller effect, thus stabilizing the layered structure during cycling. Furthermore, the use of nontoxic and low-cost raw materials benefits future commercialization and reduces the risk of environmental pollution. As a result, the HE-CFMO cathode exhibits a super cycling performance with a 95% capacity retention after 300 cycles. This work provides a promising strategy to improve the structure stability and reaction kinetics of cathode materials for SIBs.

Bifunctional modulation of Li-rich layered oxide cathode material via W-modification for improved electrochemical performance

Lithium-rich layered oxides (LRLOs) have raised the greatest attention to the high-energy-density Li-ion batteries. Nevertheless, the undesirable interfacial side reactions and the structure transformation cause fast voltage fading and poor capacity retention of LRLO cathodes, which extremely prevent their practical application. Surface coating or lattice doping has been an effective strategy to improve its electrochemical properties. However, the general performance of the material can only be limitedly promoted. Herein, we proposed a bifunctional modulation of LRLO cathodes coupled by bulk-phase W-doping and surficial Li2WO4 nanocoating of LRLOs using a facile synchronous lithiation strategy under a high-temperature solid-state treatment. The modified material (2 mol% W6+ modified) showed a distinguished discharge capability of 260.5 mAh/g at 0.1 C after 50 cycles. Meanwhile, a competitive capacity retention of 95.38% at 1 C after 100 cycles was achieved. The splendid electrochemical performance can be the result of the increased interlayer spacing for enhancing Li+ diffusion kinetics and the stronger W–O bond for alleviating oxygen release after W-doping and Li2WO4 nanocoating, which not only accelerates the Li+ transfer rate as its fast Li+ transfer channels but also act as a transitional interface layer to restrain the interfacial adverse reactions.

Modification study of Mg/W-doped LiNi0.9Mn0.1O2 layered oxide cathode materials for lithium-ion batteries

Modification study of Mg/W-doped LiNi0.9Mn0.1O2 layered oxide cathode materials for lithium-ion batteries

Enhanced cyclability and energy density of mid-nickel layered oxide cathode material LiNi0.55Mn0.25Co0.20O2 by niobium doping via solvothermal method

Ni-based layered oxide materials are among the most promising cathode materials for the next generation of lithium-ion batteries due to their higher energy capacity. However, capacity decay occurs due to degradation mechanisms that reduce the electrochemical performance of this type of material. This work aims to synthesize Nb-doped LiNi0.55Mn0.25Co0.20O2 (Nb-NCM) materials via the solvothermal method to enhance the cyclability and energy density of the layered oxide cathode. The effects of Nb doping on the microstructure and the electrochemical performance of the cathodes are investigated. The introduction of the contents of Nb expands the structural lattice parameters and decreases the Li+/Ni2+ cation mixing degree of the NCM cathode. Furthermore, the Nb doping enhances the electrochemical activity of LiNi0.55Mn0.25Co0.20O2, increasing its initial discharge capacity to 169.61 mAhg−1 when 1% of Nb was used as a dopant (1%Nb-NCM) in contrast to the capacity of 149.45 mAhg−1 presented by the pristine material. The modified 1.0%Nb-NCM material also exhibits remarkable cycling performance with a capacity retention of 92.7% after 100 cycles at the rate of 1 C (2.8–4.3 V). This work suggests a rational strategy for high-performance cathode for lithium-ion batteries, proposing the extension of Nb doping to enhance Ni-mid material's cyclability.

Effect of Rare Earth Ion Doping on the Performance of Lithium-Rich Cathode Materials for Lithium-Ion Batteries

Lithium-rich layered oxide cathode materials have the advantages of a high voltage and a high specific capacity. Their commercial applications have however been impeded by some disadvantages such as low initial coulombic efficiency and low cycle life. To overcome these issues, rare earth ion-doped lithium-rich layered oxide cathode materials are investigated in this work. The irreversible release of O2- in Li2MnO3 is suppressed by rare earth ions doping, which enhanced the initial coulombic efficiency of the materials. Meanwhile, the rare-earth ion radius used for doping is larger than the Mn4+ radius, which enlarges the (003)-crystalline plane spacing, resulting in a significant enhancement of the rate performance of the material.

Performance improvement strategies of boron-doped lithium-rich layered oxide cathode materials for wide temperature condition

Herein, the boron-doped Li-rich materials are prepared by rapid nucleation-assisted solvothermal and high-temperature method. In this work, the effects of boron doping on crystal structure and cycling performances of as-prepared materials were investigated. The material characterization results show that the introduction of B reduces the TM valence, enlarges the (003) space distance, and modulates the local crystal structure, which may change the electrochemical performance of as-prepared samples. Li1.2Ni0.24Co0.08Mn0.48B0.02O2 (LLNCMBO-2) showed an increase in discharge capacity of 36.5 mAh g−1 at 0.1 C compared to the pristine sample. The LLNCMBO-2 exhibit high capacity retention of 85.50 % after 200 cycles with a voltage decay of only 254.9 mV. Additionally, the results of wide temperature testing show that the electrochemical performance of boron-doped samples improved evidently.

Surface Catalytic Repair for the Efficient Regeneration of Spent Layered Oxide Cathodes.

Direct recycling is considered to be the next-generation recycling technology for spent lithium-ion batteries due to its potential economic benefits and environmental friendliness. For the spent layered oxide cathode materials, an irreversible phase transition to a rock-salt structure near the particle surface impedes the reintercalation of lithium ions, thereby hindering the lithium compensation process from fully restoring composition defects and repairing failed structures. We introduced a transition-metal hydroxide precursor, utilizing its surface catalytic activity produced during annealing to convert the rock-salt structure into a layered structure that provides fast migration pathways for lithium ions. The material repair and synthesis processes share the same heating program, enabling the spent cathode and added precursor to undergo a topological transformation to form the targeted layered oxide. This regenerated material exhibits a performance superior to that of commercial cathodes and maintains 88.4% of its initial capacity after 1000 cycles in a 1.3 Ah pouch cell. Techno-economic analysis highlights the environmental and economic advantages of surface catalytic repair over pyrometallurgical and hydrometallurgical methods, indicating its potential for practical application.

Layered Oxide Cathode Materials for Sodium-Ion Batteries: A Mini-Review

Layered Oxide Cathode Materials for Sodium-Ion Batteries: A Mini-Review

Lithium-rich manganese-based layered oxide cathode materials for lithium-ion batteries modified by MoS2 coatings with two-dimensional graphene-like structures

Lithium-rich manganese-based layered oxide cathode materials (LRMCs) have some unique advantages such as high theoretical capacity (≥ 250 mAh g−1) and high energy density. Therefore, they are deemed as a kind of cathode material for lithium-ion batteries with an excellent prospect of application. However, the redox of oxygen anion is able to generate irreversible lattice oxygen loss, leading to irreversible loss of capacity, bringing about a sharp drop of working voltage, and seriously restricting the commercialization of LRMCs. In this paper, MoS2 coating with two-dimensional graphene-like structure was coated on the surface of LRMCs materials for improving the cycling stability and rate performance. The MoS2 coating can provide a two-dimensional diffusion channel for the migration of lithium-ions, which facilitates the fast release of lithium-ions during cycling process. The results show that the first discharge capacity, initial Coulomb efficiency and rate performance of LRMCs are improved. When the current density is 1 C, the first discharge specific capacity of LRMCs@MoS2 reaches 227.69 mAh g−1, and the capacity retention ratio is 84.98 % after 100 cycles. When the current density is 5 C, it can still provide a discharge specific capacity of 137.87 mAh g−1, demonstrating excellent electrochemical performance. This study comes up a simple and practical idea to realize the modification of cathode materials for high performance lithium-ion batteries.

Facilitating superior electrochemical efficacy and ultra rapid kinetic in Co/Ni-free layered oxides for sodium-ion batteries with phosphate-growing layer fast ion conductors

Co/Ni-free layered oxides have garnered significant interest due to their environmental friendliness and facile synthesis methodologies, while facing major challenges of inferior cycling stability and rate capability. Addressing these drawbacks necessitates the enhancement of the surface properties of Co/Ni-free layered oxides. This work introduces a Co/Ni-free layered oxide, Na0.67Mn0.65Fe0.3Al0.05O2 (NMFA), which has been subjected to phosphate-based surface engineering. This targeted surface modification aims to augment the specific surface area and establish a protective layer on NMFA. Such improvements are critical for expanding the effective electrochemical reaction zone, broadening sodium ion diffusion pathways, curtailing the P2-OP4 phase transition, and reducing the activation energy for interfacial charge transfer. This multifaceted surface treatment epitomizes the ingenious design and realization of advanced Co/Ni-free layered oxide cathode materials through straightforward processing techniques. Notably, the NMFA subjected to 3%-AlPO4 surface modification demonstrated an initial discharge capacity of 189.1 mAh/g at 0.1C, maintaining its capacity after 500 cycles at 10C. Additionally, DFT calculations corroborate that such surface growth can bolster electrical conductivity, restrain oxygen liberation and foster sodium ion migration. This elucidates that the phosphate growth layer serves as the oxygen reservoir. Accordingly, this investigation propounds a promising avenue to circumvent the challenges confronting Co/Ni-free layered oxides, thus paving the way for the development of high-performance cathode materials.

A Novel 4-Fluorophenyl Isocyanate Additive Constructing Solid Cathodes-Electrolyte Interface for High-Performance Lithium-Ion Batteries.

Building a stable cathode-electrolyte interface (CEI) is crucial for achieving high-performance layered metal oxide cathode materials LiNixCoyMn1-x-yO2 (NCM). In this work, a novel 4-fluorobenzene isocyanate (4-FBC) electrolyte additive that contains isocyanate and benzene ring functional groups is proposed, which can form robust and homogeneous N-rich and benzene ring skeleton CEI film on the cathode surface, leading to significant improvement in the electrochemical performance of lithium-ion batteries. Taking LiNi0.5Co0.2Mn0.3O2 (NCM523) as an example, the NCM523/SiO@Graphite pouch full cells with electrolytes containing a mass fraction of 1% 4-FBC additives demonstrate improved capacity retention after 200 cycles, retaining capacity retention rates of 81.3%, which is much higher than that of 39.1% without additive. The improvement can be ascribed to the mitigation of electrolyte decomposition and inhibition of transition metal ions the dissolution from the cathode material due to the stable CEI film. Moreover, the electrochemical performance enhancement can also be achieved in high voltage and Ni-rich cathode materials, indicating the universality and effectiveness of this strategy for the practical applications of high energy density lithium-ion batteries.

Understanding the Carbon Additive/Sulfide Solid Electrolyte Interface in Nickel-Rich Cathode Composites and Prioritizing the Corresponding Interplay between the Electrical and Ionic Conductive Networks to Enhance All-Solid-State-Battery Rate Capability.

All-solid-state lithium batteries, including sulfide electrolytes and nickel-rich layered oxide cathode materials, promise safer electrochemical energy storage with high gravimetric and volumetric densities. However, the poor electrical conductivity of the active material results in the requirement for additional conducive additives, which tend to react negatively with the sulfide electrolyte. The fundamental scientific principle uncovered through this work is simple and suggests that the electrical network benefits associated with the introduction of short-length carbons will eventually be overpowered by the increase in bulk resistance associated with their instability in the sulfide electrolyte. However, applying just the right amount of short carbon fibres minimizes degradation of the sulfide solid electrolyte and maximizes the electron movement. Therefore, we propose the application of a low-weight-percent carbon nanotubes (CNTs) coating on the nickel-rich cathode LiNi0.8Co0.1Mn0.1O2 (NCM811) along with large-aspect-ratio carbon nanofibers (CNFs) as the primary conductive additive. When only 0.3 wt % CNTs was utilized with 4.7 wt % CNFs, an initial Coulombic efficiency of 83.55% at 0.05C and a notably excellent capacity retention of 90.1% over 50 cycles at 0.5C were achieved along with a low ionic resistance. This work helps to confirm the validity of applying short carbon pathways in sulfide-electrolyte-based cathode composites and proposes their combination with a larger primary carbon additive as a solution to the ongoing all-solid-state battery rate and instability issues.

Tailoring planar strain for robust structural stability in high-entropy layered sodium oxide cathode materials

Tailoring planar strain for robust structural stability in high-entropy layered sodium oxide cathode materials

Ti-Substituted O3-NaNi0.5Mn0.3Ti0.2O2 Material with a Disordered Transition Metal Layer and a Stable Structure.

O3-type NaNi0.5Mn0.5O2 (NNM) is very competitive for sodium-ion batteries (SIBs) due to its high capacity and easy production. Nevertheless, the intricate phase transitions during the charging-discharging significantly impede its practical application. This paper proposes a strategy for successfully synthesizing NaNi0.5Mn0.3Ti0.2O2 (NNMT) by combining coprecipitation and a high-temperature solid-state method. This method introduces Ti elements while retaining the electrochemically active Ni2+ content, thus, the NNMT has a high initial specific capacity of 151.4 mAh g-1 at 1 C. It is demonstrated that introducing Ti4+ leads to the transition metal layers becoming disordered by ex situ XRD, thus mitigating the irreversible phase transition of the material. In addition, Ti4+ does not have an outer electron, which can reduce electron delocalization in the transition metal layer and improve the material's cyclic stability. The NNMT possesses a capacity retention rate of 60.66% after 150 cycles, much higher than the initial NNM's 18.96%. It also exhibits an excellent discharge capacity of 86.8 mAh g-1 at 5 C. In conclusion, the cycling and rate performance of the Ti-substituted NNMT are greatly improved without capacity loss, which offers innovative concepts for the modification means of the SIBs layered oxide cathode materials.

Comprehensive Review of Li-Rich Mn-Based Layered Oxide Cathode Materials for Lithium-Ion Batteries: Theories, Challenges, Strategies and Perspectives.

Lithium-rich manganese-based layered oxide cathode materials (LLOs) have always been considered as the most promising cathode materials for achieving high energy density lithium-ion batteries (LIBs). However, in practical applications, LLOs often face some key problems, such as low initial coulombic efficiency, capacity/voltage decay, poor rate performance and poor cycle stability. It seriously shortens the lifespan of lithium-ion batteries and hinder the large-scale commercial application of LLOs. Herein, firstly, the basic theories of LLOs were systematically reviewed, including the structural characteristics, the working mechanism of LLOs, the preparation methods of LLOs (liquid phase co-precipitate method, sol-gel method, hydrothermal synthesis method, solid phase method, low heat solid-phase method, high temperature solid-state method etc.), and electrochemical characteristics of LLOs (first charge discharge characteristics and reversible efficiency, cycling performance, high and low temperature performance and thermal stability etc.). Then, key challenges faced by LLOs were systematically discussed. Finally, the LLOs modification strategies used to address these challenges (element doping, surface modification, defect engineering, structural and morphological control etc.) were elaborated in detail. This important review provides potential insights and directions for further improving the electrochemical performance of LLOs, and provides a necessary theoretical basis for accelerating the large-scale commercial application of LLOs. It possesses important scientific research value and far-reaching social significance.

Layered oxide cathodes: A comprehensive review of characteristics, research, and development in lithium and sodium ion batteries

AbstractLayered oxide materials are widely used in the field of energy storage and conversion due to their high specific energy, high efficiency, long cycle life, and high safety. Herein, We summarize the latest research progress in the field of layered metal oxide cathode materials from three aspects: challenges faced, failure mechanisms, and modification methods. We also compare the characteristics of lithium‐based layered oxides and sodium‐based layered oxides, and predict future development directions. The layered oxide cathode materials for sodium‐ion batteries and lithium‐ion batteries exhibit overall structural and operational similarities. There are also some differences, such as lattice parameters and application extent. Sodium‐ion battery cathode materials need to explore new materials and address structural instability issues, while lithium‐ion batteries require finding alternative materials and improving production efficiency. Future challenges for both types of materials include enhancing capacity and cycle performance, elucidating deep mechanisms, reducing costs, and improving resource sustainability. Future development should focus on balancing cycle stability and charge cut‐off voltage to meet the growing demand for battery applications.

Visualizing Reaction Distributions for Materials Validation and Failure Analysis in Li-Ion Batteries

A real-time, high-throughput visualization technique for heterogeneity in lithium-ion battery (LIB) electrodes is necessary to understand battery performance on a mechanistic level. Our group, along with others, has seen that battery performance is governed by short range (<20 um) electron transfer between the active material and carbon binder domain (CBD) within electrodes [1]–[3]. Available imaging techniques for visualizing the electronic connectivity of LIB electrodes are limited to nanoscale, single particle resolutions using sophisticated synchrotron X-ray or electron microscopy [4]–[6]. Optical microscopy offers the correct spatial resolution for visualizing the submicron connection of active particles to CBD, but is limited by colorimetry of electrode materials- with graphite being the exception due to its visible color change during lithiation [7]. There is a rapidly growing body of research interested in studying the ionic diffusion pathways of Li-ion using operando optical microscopy, however none currently exist for studying the submicron electronic connectivity through a facile, operando approach- especially under a industrially applicable lens [8]. To the best of our knowledge, this study presents the first spatially- and time- resolved technique for visualizing the electronic connectivity of commercial LIB electrodes using operando electrochemical fluorescent microscopy (EFM). This technique relies on the principle of electrofluorochromism, which we use to our advantage for a simple electrochemical system involving heterogeneous electron transfer. This allows us to use fluorescence as a real-time tracker for electronic heterogeneity, where electronic ‘dead-zones’ present as non-fluorescent regions in 2D images.Using our technique, we visualize commonly used commercial LIB electrodes (carbon content 1-4%, regimented processing), including NMC (LiNixMnyCo1-x-yO2), LFP (LiFePO4), and LCO (LiCoO2) against formulaically similar in-house made LIB electrodes (< 3.5% carbon content) as a proof of concept. We first validate the efficacy of this technique by testing commercial NMC, with a flaked off piece of active material, to show that areas of electronic discontinuities can in fact be represented by non-fluorescence (Fig.1.) We also find that when compared to commercial electrodes, those which are fabricated in house reveal isolated active particles, agglomerated carbon islands, and dead zones, undiscernible by brightfield imaging (Fig. 2.) Global feature extraction is performed on post-processed images to quantify electrode topology and evaluate electronic connectivity of active particles of battery electrodes, as well as heterogeneous mapping to determine the heterogeneity index of electrodes imaged. Testing our technique on low- and high- performing electrodes from an established library of coin-cell data allows for a straightforward way of correlating performance metrics to heterogeneity features. This quick (<1hr), reproducible visualization technique is general enough to be used to study the electronic connectivity of emerging new battery electrodes, as well as verify commercially available ones. Using this approach to verify LIB electrodes prior to assembly could save months to years of battery testing by being used as an alternative to lengthy full cell testing.[1] S. L. Morelly, N. J. Alvarez, and M. H. Tang, “Short-range contacts govern the performance of industry-relevant battery cathodes,” Journal of Power Sources, vol. 387, pp. 49–56, May 2018, doi: 10.1016/j.jpowsour.2018.03.039.[2] R. M. Saraka, S. L. Morelly, M. H. Tang, and N. J. Alvarez, “Correlating Processing Conditions to Short- and Long-Range Order in Coating and Drying Lithium-Ion Batteries,” ACS Appl. Energy Mater., vol. 3, no. 12, pp. 11681–11689, Dec. 2020, doi: 10.1021/acsaem.0c01305.[3] J. Entwistle, R. Ge, K. Pardikar, R. Smith, and D. Cumming, “Carbon binder domain networks and electrical conductivity in lithium-ion battery electrodes: A critical review,” Renewable and Sustainable Energy Reviews, vol. 166, p. 112624, Sep. 2022, doi: 10.1016/j.rser.2022.112624.[4] S. Li et al., “Mutual modulation between surface chemistry and bulk microstructure within secondary particles of nickel-rich layered oxides,” Nat Commun, vol. 11, no. 1, Art. no. 1, Sep. 2020, doi: 10.1038/s41467-020-18278-y.[5] P.-C. Tsai et al., “Single-particle measurements of electrochemical kinetics in NMC and NCA cathodes for Li-ion batteries,” Energy Environ. Sci., vol. 11, no. 4, pp. 860–871, Apr. 2018, doi: 10.1039/C8EE00001H.[6] A. Singer et al., “Nucleation of dislocations and their dynamics in layered oxide cathode materials during battery charging,” Nat Energy, vol. 3, no. 8, Art. no. 8, Aug. 2018, doi: 10.1038/s41560-018-0184-2.[7] Y. Yamagishi, H. Morita, Y. Nomura, and E. Igaki, “Visualizing Lithiation of Graphite Composite Anodes in All-Solid-State Batteries Using Operando Time-of-Flight Secondary Ion Mass Spectrometry,” J. Phys. Chem. Lett., vol. 12, no. 19, pp. 4623–4627, May 2021, doi: 10.1021/acs.jpclett.1c01089.[8] A. J. Merryweather, C. Schnedermann, Q. Jacquet, C. P. Grey, and A. Rao, “Operando optical tracking of single-particle ion dynamics in batteries,” Nature, vol. 594, no. 7864, Art. no. 7864, Jun. 2021, doi: 10.1038/s41586-021-03584-2. Figure 1

Operando Electrochemical Fluorescent Microscopy to Predict Li-Ion Battery Performance

A real-time, high-throughput visualization technique for heterogeneity in lithium-ion battery (LIB) electrodes is necessary to understand battery performance on a mechanistic level. Our group, along with others, has seen that battery performance is governed by short range (<20 um) electron transfer between the active material and carbon binder domain (CBD) in electrodes [1]–[3]. Available imaging techniques for visualizing the electronic connectivity of LIB electrodes are limited to nanoscale, single particle resolutions using sophisticated synchrotron X-ray or electron microscopy [4]–[6]. Optical microscopy offers the correct spatial resolution for visualizing the submicron connections of active particles to CBD, but is limited by the colorimetry of electrode materials- with graphite being the exception due to its visible color change during lithiation [7]. There is a rapidly growing body of research interested in studying the ionic diffusion pathways of Li-ion using operando optical microscopy, however none currently exist for studying the submicron electronic connectivity using an operando approach- especially under a industrially applicable lens [8]. To the best of our knowledge, this study presents the first spatially- and time- resolved technique for visualizing the electronic connectivity of commercial LIB electrodes using operando electrochemical fluorescent microscopy (EFM). This technique relies on the principle of electrofluorochromism, which we use to our advantage for a simple electrochemical system involving heterogeneous electron transfer. This allows us to use fluorescence as a real-time tracker for electronic heterogeneity, where electronic ‘dead-zones’ present as non-fluorescent regions in 2D images.Using this technique, we visualize commonly used commercial LIB electrodes (carbon content 1-4%, regimented processing), including NMC (LiNixMnyCo1-x-yO2), LFP (LiFePO4), and LCO (LiCoO2) against formulaically similar in-house made LIB electrodes (< 3.5% carbon content) as a proof of concept. We first validate the efficacy of this technique by testing commercial NMC, with a flaked off piece of active material, to show that areas of electronic discontinuities can in fact be represented by non-fluorescence (Fig.1.) We also find that when compared to commercial electrodes, those which are fabricated in house reveal isolated active particles, agglomerated carbon islands, and dead zones, undiscernible by brightfield imaging (Fig. 2.) Global feature extraction is performed on post-processed images to quantify electrode topology and evaluate electronic connectivity of active particles of battery electrodes, as well as heterogeneous mapping to determine the heterogeneity index of electrodes imaged. Testing our technique on low- and high- performing electrodes from an established library of coin-cell data allows for a straightforward way of correlating performance metrics to heterogeneity features. This quick (<1hr), reproducible visualization technique is general enough to be used to study the electronic connectivity of emerging new battery electrodes, as well as verify commercially available ones. Using this approach to verify LIB electrodes prior to assembly could save months to years of battery testing by being used as an alternative to lengthy full cell testing.[1] S. L. Morelly, N. J. Alvarez, and M. H. Tang, “Short-range contacts govern the performance of industry-relevant battery cathodes,” Journal of Power Sources, vol. 387, pp. 49–56, May 2018, doi: 10.1016/j.jpowsour.2018.03.039.[2] R. M. Saraka, S. L. Morelly, M. H. Tang, and N. J. Alvarez, “Correlating Processing Conditions to Short- and Long-Range Order in Coating and Drying Lithium-Ion Batteries,” ACS Appl. Energy Mater., vol. 3, no. 12, pp. 11681–11689, Dec. 2020, doi: 10.1021/acsaem.0c01305.[3] J. Entwistle, R. Ge, K. Pardikar, R. Smith, and D. Cumming, “Carbon binder domain networks and electrical conductivity in lithium-ion battery electrodes: A critical review,” Renewable and Sustainable Energy Reviews, vol. 166, p. 112624, Sep. 2022, doi: 10.1016/j.rser.2022.112624.[4] S. Li et al., “Mutual modulation between surface chemistry and bulk microstructure within secondary particles of nickel-rich layered oxides,” Nat Commun, vol. 11, no. 1, Art. no. 1, Sep. 2020, doi: 10.1038/s41467-020-18278-y.[5] P.-C. Tsai et al., “Single-particle measurements of electrochemical kinetics in NMC and NCA cathodes for Li-ion batteries,” Energy Environ. Sci., vol. 11, no. 4, pp. 860–871, Apr. 2018, doi: 10.1039/C8EE00001H.[6] A. Singer et al., “Nucleation of dislocations and their dynamics in layered oxide cathode materials during battery charging,” Nat Energy, vol. 3, no. 8, Art. no. 8, Aug. 2018, doi: 10.1038/s41560-018-0184-2.[7] Y. Yamagishi, H. Morita, Y. Nomura, and E. Igaki, “Visualizing Lithiation of Graphite Composite Anodes in All-Solid-State Batteries Using Operando Time-of-Flight Secondary Ion Mass Spectrometry,” J. Phys. Chem. Lett., vol. 12, no. 19, pp. 4623–4627, May 2021, doi: 10.1021/acs.jpclett.1c01089.[8] A. J. Merryweather, C. Schnedermann, Q. Jacquet, C. P. Grey, and A. Rao, “Operando optical tracking of single-particle ion dynamics in batteries,” Nature, vol. 594, no. 7864, Art. no. 7864, Jun. 2021, doi: 10.1038/s41586-021-03584-2. Figure 1

A New High-Valent Fe Redox Couple in Intercalation Electrodes

The overwhelming majority of layered oxide cathode materials are based on the redox activity of expensive and scarce transition metals like Co and Ni. While the Fe-redox based material LiFePO4 has become increasingly attractive due to its low cost, its low gravimetric energy density and relatively low operating voltage limit its use cases. A high-voltage Fe-based layered oxide cathode would provide high energy density utilizing the redox-activity of the most abundant transition metal in Earth’s crust, but such a material that provides stable and reversible electrochemical performance remains elusive. Indeed, high-voltage Fe-redox in oxides is plagued by cation disorder and oxygen dimerization, which leads to capacity fading and large voltage hysteresis (> 1 V).[1]In contrast, the layered oxide cathode Li4FeSbO6 (equivalently, Li[Li1/3Fe1/3Sb1/3]O2, abbreviated LFSO) exhibits <0.2 V of hysteresis, and a discharge plateau at 4.2 V versus Li/Li+ with two-electron capacity.[2] Both the exceptional electrochemical reversibility of this material and its phase separating nature upon (de)intercalation raise questions about the origin of these properties that are unusual for layered Fe oxide cathodes. In this work, we will discuss our efforts to probe the electronic structure of LFSO with Fe L–edge x–ray absorption (XAS) and 57Fe Mössbauer spectroscopy, as well as O K–edge resonant inelastic x–ray scattering spectroscopy (RIXS). The combination of these element-specific and valence-state sensitive techniques, in conjunction with charge-transfer multiplet and density functional theory calculations, allows us to reveal the electronic structure changes at Fe and O as a function of state of charge for the first time. Correlating these electronic structure changes with synchrotron diffraction measurements, we reveal a unique redox compensation mechanism that readily rationalizes the exceptional electrochemical reversibility, unlocking a new direction for high-voltage, Fe-based redox systems.

First-Principle Insight of Synergistic Modification Mechanism in P2-Type Layered Oxide Cathode Material with Anionic Redox Activity for Sodium-Ion Batteries

Layered oxides exhibiting anionic redox activity have gained attention as a promising material in both Na-ion batteries owing to their additional capacity provided through oxygen redox chemistry. However, unfavorable side effects such as irreversible phase transformation, hysteresis, and gas evolution, usually arise during the stabilization process of the unstable electron holes generated by the redox reaction of oxygen. To address these challenges, we co-dope Cu and Ca in the pristine Nax[Mg0.28Mn0.72]O2 (NMMO) and propose the P2-type NaxCa0.03Mg0.22Cu0.11Mn0.67O2 (NCaMCMO) Na-deficient cathode material which demonstrates high specific capacity with minimal phase change. In this work, we employed the density functional theory (DFT) calculations to investigate the underlying mechanisms of the synergistic modification strategy in both transition metal and alkali metal layers. The substitution of electrochemically active Cu induced variations in the electronic structure near the Fermi level, indicating an inherent change in redox chemistry. The computational results of the local structure provide a deeper understanding of the oxygen-stabilizing effect of Cu. Furthermore, we analyze the nature of the Ca insertion as a pillar in an alkali-metal layer, which mitigates phase transformation to the kinetically unfavorable O2 phase through phase energy comparison. The calculations manifest that Ca doping effectively extends the P2 phase into a deeper charging state. This work elucidates fundamental mechanisms for enhancing cathode materials in future battery design.