Layered Oxide Materials Research Articles

A bimetal strategy for suppressing oxygen release of 4.6V high-voltage single-crystal high-nickel cathode

High-voltage cathode materials, such as single-crystal high-nickel layered oxide materials, are a necessary condition for achieving high energy density lithium-ion batteries, but they have to be accompanied by the structural instability and irreversible release of lattice oxygen during operation, posing serious safety hazards. Here, to solve the lattice oxygen release issue of single-crystal high-nickel cathode, we propose an improved strategy for overall cathode by synchronously addressing interface and lattice instability, ensuring stable operation at a high voltage up to 4.6 V. By Al-doping, in the bulk phase, we intensify the charge transfer between transition metals and oxygen, and the columnar effect caused by doped atoms effectively alleviates internal strain, thereby significantly limiting lattice shrinkage and then suppressing oxygen release. On the other hand, the protective layer of LiNbO3 as the fast ion conductor formed at the cathode interface suppresses parasitic reactions and hinders lattice oxygen loss caused by dissolution of transition metals. Therefore, after 200 cycles at a cut-off voltage of 4.6 V, our cathode material still maintains a capacity retention rate of 89.1%. Density functional theory (DFT) calculations predict the effective suppression of oxygen release for the modified cathode materials, which has been further confirmed by differential electrochemical mass spectrometry (DEMS) tests. This work provides a new perspective for solving the problem of oxygen release under high cut-off voltage conditions for single crystal high nickel cathode.

Regulating local chemical environment in O3-type layered sodium oxides by dual-site Mg2+/B3+ substitution achieves durable and high-rate cathode

The O3-Na0.85Ni0.2Fe0.4Mn0.4O2 layered oxide cathode material possesses the advantages of high specific capacity, low cost, and simple synthesis. However, sluggish kinetics and complicated phase transition caused by the large size difference between Na+ and tetrahedral gaps lead to poor rate and cycling performance. Therefore, a scalable and feasible strategy was proposed to modulate local chemical environment by introducing Mg2+ and B3+ into O3-Na0.85Ni0.2Fe0.4Mn0.4O2, which can distinctly improve kinetic transport rate as well as electrochemical performance. The capacity retention of O3-(Na0.82Mg0.04)(Ni0.2Fe0.4Mn0.4)B0.02O2 (NFMB) increases from 43.3% and 12.4% to 89.5% and 89.0% at 1 C and 3 C after 200 cycles, respectively. Moreover, the electrode still delivers high rate capacity of 93.9 mAh/g when current density increases to 10 C. Mg2+ ions riveted on Na layer act as a “pillar” to stabilize crystal structure and inhibit structural change during the desodiumization process. B3+ ions entering tetrahedral interstice of the TM layer strengthen the TM-O bond, lower Na+ diffusion energy barrier and inhibits the slip of TM layer. Furthermore, the assembled full batteries with the modified cathode material deliver a high energy density of 278.2 Wh/kg with commercial hard carbon as anode. This work provides a strategy for the modification of high-performance SIB layered oxide materials to develop the next-generation cost-effective energy storage grid systems.

Rational design of cationic ratio tuned high-performance P2/O3 bi-phase layered oxide materials for sodium-ion batteries

Layered oxides are the widely investigated cathodes for sodium-ion batteries (SIBs), especially their pure phases (e.g., P2, O3). In this work, we report a series of Mn-Ni-Fe based cathode materials with P2/O3 bi-phase, which possesses advantages of both P2 and O3 structures. At first, the manuscript shows a synthesis phase diagram of Na0.83MnxNiyFe1-x-yO2 to pre-screen and select the P2/O3 bi-phase material Na0.83Mn1/2Ni1/3Fe1/6O2. Then, it is found that the cationic ratio has a significant impact on the phase formation. The structure of the materials gradually changes with the various of the Mn/Ni ratio. When the Mn/Ni ratio reaches 3/2, P2/O3 bi-phase is formed. Moreover, Fe content will influence the P2/O3 ratio in the bi-phase material. In particular, the synthesized bi-phase Na0.83Mn3/6Ni2/6Fe1/6O2 has a P2/O3 ratio of 71/29 wt%. It delivers a high specific capacity of 136.6 mA h g−1 (at current density 20 mA g−1) between 2.0 and 4.0 V and 94.8% retention (at current density 100 mA g−1) after 100 cycles. In addition, an 85.6 mA h g−1 discharge capacity can be maintained at a superior high current density of 2000 mA g−1. The work offers critical guidance to the rational design of the bi-phase layered cathode materials.

Probing the account of phase transition upon electrochemical cycling of the P2-Na0.67Ni0.15Fe0.2Mn0.65O2 layered oxide cathodes for sodium-ion batteries

Layered P2-Na0.67Ni0.15Fe0.2Mn0.65O2 (P2-NFM) cathode material has attracted great attention in sodium-ion batteries due to its high theoretical capacity, low cost, and environmental friendliness. However, P2-NFM exhibits irreversible phase transition and slip of transition metal layers in the high voltage range during charging process, leading to a gradually declined performance of the cathode material. It is therefore necessary to investigate the mechanism of phase transition of P2-NFM as well as the effect of phase transition on its performance. Herein, utilizing ex situ x-ray diffraction spectroscopy and x-ray photoelectron spectroscopy, the crystal structure and TM (transition-metal) bonding changes caused by phase transition are elucidated. It is found that P2-NFM is prone to undergo an irreversible P2-O2 phase transition at high voltage, causing changes in lattice parameters and rapid capacity decay. The irreversible phase transition is mainly due to he dynamic transformation of valence states of Fe and Ni in P2-NFM materials at high voltage. It is this process that results in irreversible fluctuations in the bond lengths between these elements and oxygen, consequently instigating interlayer slip within the material. Besides, the charge compensation mechanism of P2-NFM has been elucidated based on the study of its initial charging process. Results show that the charge compensation is mainly contributed by Ni and Fe in the high voltage range, while by a small amount of Mn in the low voltage range. It reveals the essential cause of the adverse phase transition of P2-NFM materials and points out the direction for improving the cycling stability of these layered oxide materials.

Enhanced electrochemical performance of lithium-rich layered oxide materials: Exploring advanced coating strategies

Enhanced electrochemical performance of lithium-rich layered oxide materials: Exploring advanced coating strategies

Facilitating the high voltage stability of NFM via transition metal slabs high-entropy configuration strategy

Sodium ion batteries, which is viewed as the potential candidate of Li-ion batteries, are now at the edge of wildly application. The layered oxide cathode materials, represented by NaNi1/3Fe1/3Mn1/3O2 (NFM), inherits the experience of success from LIBs are now promising of commercialization. Yet, the relative low operation voltage of NFM causing by the existence of Fe migration above 4.2 V hinder its further application nowadays. Herein, high-entropy O3-type NaMg0.08Cu0.12Ni0.2Fe0.2Mn0.2Ti0.2O2(HNFM) was proposed addressing working voltage at 4.3 V with the inhibition of large amount of Fe migration. Electrochemical test showed a specific capacity of 131 mAh g−1 was achieved within the voltage range from 2.0 to 4.3 V at current density of 0.2 C which boosted an energy density of up to 425 Wh kg−1. After 200 cycles at a 1 C current density, the capacity retention remains at 84 %. In-situ XRD analysis revealed that HNFM alleviated phase transition at high voltage compared to NFM thus it can withstand a wide operating voltage range of 2–4.3 V. DFT calculations demonstrated that transition metal slabs with high-entropy configurations could effectively suppress the migration of Fe ions from the transition metal slabs to the Na layer, thereby further enhancing the material's stability during cycling. These research findings shed light on the high-voltage operating for the layered oxide materials which provide the novel insight of the material design and inspire the commercialization of sodium ion batteries.

Recycling of protective layer of Ni rich layered oxide material in Li ion batteries

We investigated the recycling of protective layer of Ni rich layered oxide–material used in Li ion batteries. Decreasing electrochemical performance of the cathode powder while leaving the powder in air was confirmed by various analyses and was found to be due to the formation of lithium residuals. The surface of the protective layer of Ni rich layered oxide was covered by the lithium residuals and that led to the cancellation of the coating effect. The residual lithium decreased and the cell performance was recovered by following a recycling process in this work. After the recycling process, the performance of the protective layer became similar to that of the layer immediately after the initial coating, and the coating layer showed a resurgence, which was confirmed by SEM and TEM images. The capacity of the initial coated Ni rich NCM and the sample after recycling was 209 and 206 mAh/g at 1C, respectively. The cycle retention for the initial coated Ni rich NCM and the sample after recycling was 93.4 and 92.6 % after 50 cycles at 1C, respectively. It is concluded that the coating layer and the electrochemical performance were recovered by the recycling process.

Practical Evaluation of Anionic Redox in Li‐rich Cathode: An Electrochemical Study

AbstractLithium‐rich (Li‐rich) manganese‐based layered oxide materials are promising candidates for positive electrode materials due to their high energy density. However, challenges such as transition metal cation migration and irreversible anionic redox hinder their application. This study employs various electrochemical methods to systematically investigate three types of cathode materials: LiNi0.6Mn0.2Co0.2O2 (NCM622), Li1.12Ni0.39Mn0.49O2 (Li1.12), and Li1.2Ni0.2Mn0.6O2 (Li1.2). The findings indicate that an increase in lithium content leads to higher participation of anions in Anion Redox Reactions (ARRs), resulting in an augmented capacity. However, this also brings about significant polarization. The activation process of Li‐rich materials triggers the ARRs mechanism, resulting in a sharp increase in resistance. Voltage drops during shelving and cycling are closely tied to the ARRs occurring at high potentials in Li‐rich materials. To make the best use of the additional capacity associated with ARRs, it is essential to adjust the formation/cycling voltage in accordance with the characteristics of positive electrode materials with varying lithium contents. This study offers valuable insights for the design and utilization of Li‐rich materials.

Solid-State Chemistry Shuffling of Alkali Ions toward New Layered Oxide Materials

Solid-State Chemistry Shuffling of Alkali Ions toward New Layered Oxide Materials

Revealing proton-coupled exchange mechanism in aqueous ion-exchange synthesis of nickel-rich layered cathodes for lithium-ion batteries

Ion exchange is a promising synthetic method for alleviating severe cation mixing in traditional layered oxide materials for lithium-ion batteries, leading to enhanced structural stability. However, the underlying mechanisms of ion exchange are still not fully understood. Such a fundamental study of the ion-exchange mechanism is needed for achieving the controllable synthesis of layered oxides with a stable structure. Herein, we thoroughly unearth the underlying mechanism that triggers the ion exchange of Ni-rich materials in aqueous solutions by examining time-resolved structural evolution combined with theoretical calculations. Our results reveal that the reaction pathway of ion exchange can be divided into two steps: protonation and lithiation. The proton is the key to achieving charge balance in the ion exchange process, as revealed by X-ray adsorption spectroscopy and inductive coupled plasma analysis. In addition, the intermediate product shows high lattice distortion during ion exchange, but it ends up with a most stable product with high lattice energy. Such apparent discrepancies in lattice energy between materials before and after ion exchange emphasize the importance of synthetic design in structural stability. This work provides new insights into the ion-exchange synthesis of Ni-rich oxide materials, which advances the development of cathode materials for high-performance lithium-ion batteries.

Routes to high-performance layered oxide cathodes for sodium-ion batteries.

Sodium-ion batteries (SIBs) are experiencing a large-scale renaissance to supplement or replace expensive lithium-ion batteries (LIBs) and low energy density lead-acid batteries in electrical energy storage systems and other applications. In this case, layered oxide materials have become one of the most popular cathode candidates for SIBs because of their low cost and comparatively facile synthesis method. However, the intrinsic shortcomings of layered oxide cathodes, which severely limit their commercialization process, urgently need to be addressed. In this review, inherent challenges associated with layered oxide cathodes for SIBs, such as their irreversible multiphase transition, poor air stability, and low energy density, are systematically summarized and discussed, together with strategies to overcome these dilemmas through bulk phase modulation, surface/interface modification, functional structure manipulation, and cationic and anionic redox optimization. Emphasis is placed on investigating variations in the chemical composition and structural configuration of layered oxide cathodes and how they affect the electrochemical behavior of the cathodes to illustrate how these issues can be addressed. The summary of failure mechanisms and corresponding modification strategies of layered oxide cathodes presented herein provides a valuable reference for scientific and practical issues related to the development of SIBs.

A two-step method to prepare P2-type layered oxide materials for stable sodium-ion batteries via a precursor and sintering temperature control

A P2-type Na0.67Ni0.2Mn0.8O2 layered oxide cathode material with excellent cyclic performance was successfully prepared via a two-step method using ultra-nano-sized precursors.

A universal multifunctional rare earth oxide coating strategy to stabilize high-nickel lithium layered oxide cathode

LiNi0.8Co0.1Mn0.1O2 (NCM811) high-nickel lithium layered oxide material has gained recognition as a promising cathode material for lithium-ion batteries (LIBs) due to its relatively high output capacity. However, the presence of high nickel content leads to capacity fading resulting from surface residue lithium and cathode-electrolyte interfacial side reactions, posing a significant threat to the cycle life for battery. In this study, we have developed an ultrathin and uniform CeO2&LiCeO2 nanoscale rare earth composite functional coating in-situ for NCM811 cathode, utilizing residual lithium and rare earth oxide. Ex-situ scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectrometer (XPS) analyses confirm the reduction in interfacial side reactions, leading to improved stability at the cathode-electrolyte interface. This improvement can be attributed to the removal of surface residual lithium and the formation of stable CeO2&LiCeO2 functional coatings. As a result, the NCM811 modified with the rare earth composite functional coating exhibits a higher capacity retention rate after 100 cycles (90.9% vs. 86.1%) and enhanced rate capacity (136 mAh g−1 vs. 117 mAh g−1) at 5 C than the NCM811. Even the designed full battery achieves an energy density as high as 253 Wh kg−1. This work presents an innovative approach to utilize residual lithium and rare earth oxide for in-situ functional coating formation, ultimately enhancing the lithium storage performance of high-nickel NCM811 cathodes.

(Invited) Designing Sustainable Battery Technologies

Sustainability in battery technologies needs to be considered from the outset, however sustainability means many things, and needs to be considered holistically from materials, manufacturing, life-time and recyclability. Three different aspects of sustainable considerations within lithium-ion and sodium-ion technology development are discussed; materials developments, cell lifetime and optimisations, and design for recycling.The cell is comprised of a nickel based layered oxide material cathode with hard carbon anode. To maximise energy density and life-time degradation of the bulk and surface of the O3-type oxides require stabilisation.1 We discuss the optimisation of a facile method for manufacturing a stabilised O3- type layered oxide via simultaneous doping and surface coating. A higher average voltage is obtained, which stabilised the high voltage phase transition to higher voltages, and results in longer-cycle life.2 To understand the sodium-ion cell in more detail, we have performed a detailed electrochemical analysis of a hard-carbon and layered oxide cathode and extracted parameters for multi-physics models. The kinetics and thermodynamics have been studied at different temperatures, and the limitations of the cell elucidated.Finally design for remanufacture is also discussed, utilising water-based binder systems we show differences in delamination and material recovery. Utilising different recycling schemes through shredding and physical processing through to disassembly processes improvements in recovery rates are required. Particularly for low value materials, where the techno-economics of the processes do not currently work. Direct recycling of materials reclaimed from the batteries, wherever possible allows value within the material design to be maintained, rather than relying directly upon elemental value. Aspects of direct loop recycling and short loop recycling are discussed with respect to current lithium-ion technologies, and the ability to directly translate this to sodium-ion.3 In conclusion three aspects for sustainability considerations are discussed with respect to the materials life-cycle; active material optimisation, longevity and life-time when in use and electrode developments for recycling.41 T. Song and E. Kendrick, J. Phys. Mater., 2021, 4, 32004.2 T. Song, L. Chen, D. Gastol, B. Dong, J. F. Marco, F. Berry, P. Slater, D. Reed and E. Kendrick, Chem. Mater., 2022, 34, 4153–4165.3 G. D. J. Harper, E. Kendrick, et al. J. Phys. Energy, 2023, 5, 021501.4 Picture created by DALL-E 2 algorithm with Nightcafe Figure 1

Multiscale Probing and Redesign of the Solid-State Synthesis Toward Defect-Free Ni-Rich Layered Cathodes

Nickel-rich lithium layered oxides (LiNixCoyMnzO2, NCM, x+y+z=1, x≥0.6)) have received tremendous attention as the most promising cathode materials for the practical development of high-energy lithium-ion batteries. However, they commonly suffer from rapid capacity decay along with structural and morphological degradation. Previous studies have unraveled that the general failure mechanism involves the mechanical deterioration of electrode particles, originating from micro-cracking in particles due to the build-up of significant anisotropic strains during phase transition and the chemical parasitic reactions with electrolytes through the crevice created. Such chemo-mechanical failures are triggered and aggravated by various structural defects, including internal void spaces, surface reconstruction layers, and intragranular nanopores, typical features of the conventionally synthesized nickel-rich layered oxide materials. It remains elusive how these defects are formed regardless of the use of single-crystalline or polycrystalline particles. A fundamental understanding of the general defect formations is thus indispensable to clarify how the synthesis process induces the formation of intrinsic defects from the precursor to the final product stage and how these defects affect the electrochemical degradation at the primary- and secondary-particle levels. Critical questions that require in-depth study include how the spatially inhomogeneous solid-state reaction begins at the interface of reacting precursors, propagates during the synthesis, and triggers the generation of defects. In this presentation, I will show the hidden synthetic mechanism of nickel-rich layered oxide materials using a combination of high-end and multi-length-scale analysis methods, including aberration-corrected TEM, in situ heating TEM with gas control, and in situ XRD. The kinetic interplay in synthesis of nickel-rich lithium layered oxide and its implications will be discussed in detail. Furthermore, the microstructural pore defects of NCN9235 during the heating process were quantitatively characterized. Based on our mechanistic understanding, we propose a redesign of solid-state synthesis pathway to achieve structurally integrated nickel-rich layered oxide cathodes.

The Particle Size Distribution of Ni-Rich NMC Particles Determines Their Electrochemical Performance at Cylindrical Li-Ion Battery Cells

Developing lithium-ion batteries with high stability and increased energy density is crucial. In this study, we examined two potential cathode materials, LiNi0.8Mn0.1Co0.1O2 (NMC80) and LiNi0.9Mn0.05Co0.05O2 (NMC90), for use in commercial lithium-ion batteries. We utilized the 18650-cylindrical cell configuration to investigate their performance. While higher Ni mole ratios typically result in high energy, they also lead to poor stability. Our findings revealed that the uniformity of NMC particles is more critical than the Ni content. As a result, NMC90 outperformed NMC80 in terms of energy density, stability, and rate capability. These results suggest that controlling the particle size of Ni-rich layered oxide material will be crucial for further developing high-performance Li-ion batteries.

Inhibiting Oxygen Redox to Boost Ni Activity Enables Highly Stable Properties in Na0.67Ni0.33Mn0.67O2

Cation doping is a conventional and effective strategy for promoting favorable properties in layered oxides. Here, Mg and Sc were used as dopants in Na0.67Ni0.33Mn0.67O2 to significantly improve the cycling stability in the high voltage range. It was found that both dopants could successfully suppress the P2 to O2 phase transition, but induced a sloping curve as well as a short high voltage plateau above 4.0 V, respectively. We demonstrate that these different electrochemical behaviors are indicative of the suppression of oxygen redox by means of resonant inelastic X-ray scattering (RIXS) measurements. Furthermore, both X-ray absorption spectroscopy (XAS) and density functional theory show that Mg doping could enhance Ni activity while simultaneously suppressing O activity. However, these results are in contrast to other Mn-based layered oxides where Mg is known to effectively trigger the oxygen redox. We address this contradiction by proposing a competing mechanism between Ni and Mg that impacts differences in oxygen activity in Na0.67MgxNi0.33-xMn0.67O2 (x≤0≤0.33). These findings will provide a new direction in understanding the effects of cation doping on the electrochemical behavior of layered oxide materials. Figure 1

Layered Oxide Material as a Highly Stable Na‐ion Source and Sink for Investigation of Sodium‐ion Battery Materials

AbstractInvestigating Na‐ion battery (SIB) materials is complicated by the absence of a well‐performing (reference) electrode material since sodium metal cannot be considered as a quasi‐reference electrode. Taking advantage of the activity of both Ni and Mn, herein, the P2‐type and Mn‐rich Na0.6Ni0.22Al0.11Mn0.66O2 (NAM) material, known to be an excellent positive electrode, is investigated as a negative electrode. To prove NAM stability as both positive and negative electrode, symmetric cells have been assembled without pre‐sodiation, which showed a reversible capacity of 73 mA h g−1 and a remarkable capacity retention of 82.6 % after 500 cycles. The outstanding cycling performance is ascribed to the high stability of the active material at both the highest and lowest Na‐ion storage plateaus and the rather limited electrolyte decomposition and solid‐electrolyte‐interphase (SEI) formation occurring. The long‐term stability of NAM at both electrodes enables its use as a “reference” electrode for the investigation of other positive and negative electrode materials for SIBs, resembling the role played by lithium titanate (LTO) and lithium iron phosphate (LFP) in LIBs.

Rapid preparation of cobalt-free lithium rich cathode materials with layered structure and excellent performance via capillary microreactors

High voltage and high energy density cathode materials are the future development trend of power batteries. Li-and Mn-rich layered oxide (LMR) materials exhibit high capacity, low cost, and environmental friendliness, making them a promising cathode material for the next generation of lithium-ion batteries. In this study, a continuous-flow process for rapid co-precipitation synthesis of LMR precursor (Mn0.75Ni0.25CO3) in capillary microreactors was developed. Due to the good mixing characteristics of the microreactor (tm=54 ms), Mn0.75Ni0.25CO3 displays a complete spherical morphology and uniform elemental distribution without adding any complexing agent during the synthesis. The reaction time can be controlled within 11.78 s. The prepared Li1.2Mn0.6Ni0.2O2 (LMR) cathode exhibits excellent properties with a high initial discharge capacity of 266.52 mAh•g−1 at 0.1C and a superior capacity retention of 93.7 % after 200 cycles at 1C. This work demonstrates that microfluidic technology presents a viable and promising approach for quickly producing lithium battery cathode precursors.

Molybdenum‐Incorporated O3‐type Sodium Layered Oxide Cathodes for High‐Performance Sodium‐Ion Batteries

Transition metal layered oxide materials with a general formula NaxMO2 (M = Ni, Mn, Co, Fe) are widely researched with various possible electrode configurations. Herein, O3‐type NaNi(1−x)/2Mn(1−x)/2MoxO2 (x = 0, 0.05,0.1) layered oxide cathode materials are synthesized by solid‐state reaction method, and its structural, thermal, and electrochemical performance in sodium ion battery is investigated. The structural analysis reveals that a single phase highly crystalline O3‐type cathode material with an irregular particle shape is formed. The introduction of molybdenum improves the thermal stability of cathode materials, which can be attributed to the improved TMO2 layers that provide stability to the material. The addition of Mo to Na‐layered oxide cathode materials enhances electrochemical performance. The developed cathode materials, the NaNi0.475Mn0.475Mo0.05O2, exhibit excellent specific discharge capacity (≈154 mAh g−1) at C/20 rate, (an increase of ≈20% when compared to the NaNi0.5Mn0.5O2) which can be attributed to the increased capacitance effect by the addition of Mo. The electrochemical impedance spectroscopy study reveals that the diffusion of Na+ into/from the host structure is rapid during the first cycle and then gradually reduces with subsequent cycling due to the formation of the solid electrolyte interface layer, which hinders Na+ migration. This has a potential effect on the improved electrochemical performance of the material.