Layered Cathode Materials Research Articles

Controlling the Microstructure of Cobalt-Free, High-Nickel Cathode Materials with Dopant Solubility for Lithium-Ion Batteries.

Microstructural engineering is becoming notably important in the realization of cobalt-free, high-nickel layered oxide cathodes for lithium-ion batteries since it is one of the most effective ways to improve the overall performance by enhancing the mechanical and electrochemical properties of cathodes. In this regard, various dopants have been investigated to improve the structural and interfacial stabilities of cathodes with doping. Yet, there is a lack of a systematic understanding of the effects of dopants on microstructural engineering and cell performances. Herein, we show controlling the primary particle size by adopting dopants with different oxidation states and solubilities in the host structure as an effective way for tuning the cathode microstructure and performance. The reduction in the primary particle size of cobalt-free high-nickel layered oxide cathode materials, e.g., LiNi0.95Mn0.05O2 (NM955), with high-valent dopants, such as Mo6+ and W6+, gives a more homogeneous distribution of Li during cycling with suppressed microcracking, cell resistance, and transition-metal dissolution compared to lower-valent dopants, such as Sn4+ and Zr4+. Accordingly, this approach offers promising electrochemical performance with cobalt-free high-nickel layered oxide cathodes.

Ultra-high nickel cobalt-free layered cathode material NM90 for power batteries modified collaboratively by La2O3 coating and La3+ doping

Ultra-high nickel cobalt-free layered cathode material NM90 for power batteries modified collaboratively by La2O3 coating and La3+ doping

Recent Advances for High-Entropy based Layered Cathodes for Sodium Ion Batteries.

In recent years, layered oxides have been extensively studied as promising cathode materials for sodium ion batteries. However, layered oxides undergo complex phase transitions during charge-discharge process, which adversely affects the electrochemical performance. High-entropy layered oxides as a unique design concept can effectively improve the cycling performance of cathode materials by virtue of the 2D ion migration channels between the layers. Based on the concepts of high-entropy and layered oxides, this paper reviews the research status of high-entropy layered oxides in the field of sodium-ion batteries, focusing on the connection between high-entropy and layered oxide phase transitions during electrochemical charging and discharging. Finally, the advantages of layered cathode materials based high-entropy are summarized, and the opportunities and challenges of future high-entropy layered materials are proposed.

Expandable Li Percolation Network: The Effects of Site Distortion in Cation-Disordered Rock-Salt Cathode Material

Cation-disordered rock-salt (DRX) materials receive intensive attention as a new class of cathode candidates for high-capacity lithium-ion batteries (LIBs). Unlike traditional layered cathode materials, DRX materials have a three-dimensional (3D) percolation network for Li+ transportation. The disordered structure poses a grand challenge to a thorough understanding of the percolation network due to its multiscale complexity. In this work, we introduce the large supercell modeling for DRX material Li1.16Ti0.37Ni0.37Nb0.10O2 (LTNNO) via the reverse Monte Carlo (RMC) method combined with neutron total scattering. Through a quantitative statistical analysis of the material's local atomic environment, we experimentally verified the existence of short-range ordering (SRO) and uncovered an element-dependent behavior of transition metal (TM) site distortion. A displacement from the original octahedral site for Ti4+ cations is pervasive throughout the DRX lattice. Density functional theory (DFT) calculations revealed that site distortions quantified by the centroid offsets could alter the migration barrier for Li+ diffusion through the tetrahedral channels, which can expand the previously proposed theoretical percolating network of Li. The estimated accessible Li content is highly consistent with the observed charging capacity. The newly developed characterization method here uncovers the expandable nature of the Li percolation network in DRX materials, which may provide valuable guidelines for the design of superior DRX materials.

Structural stabilizing action of terbium cation and phosphate anion to layered transition-metal oxide cathodes

The capacity decay and safety issues of layered cathodes caused by structural deterioration upon deeply delithiated state, have impeded the further large-scale commercial-used of layered transition-metal cathodes in advanced lithium-ion batteries. In this work, the terbium cation and phosphate anion are doped homogeneously into LiCoO2 and LiNi0.83Co0.11Mn0.06O2 cathodes via the facile solid phase reaction method. We found that the lattice oxygen can be stabilized by the introduction of the Tb element, leading to the mitigation of structural degradation. More impressively, the PO43− polyanion possesses a benign binding affinity for Li-ions, further accelerating Li-ion transportation. Theoretically, the incorporation of the Tb element into the crystal lattice can alleviate oxygen redox activity in the high delithiation state. Thus, the introduction of an appropriate content of anion and cation dopants synergistically modulates the robust layered structure to suppress structural collapse during cycling. Consequently, the Tb element and PO43− polyanion co-doped LiNi0.83Co0.11Mn0.06O2 (a capacity of 179.3 mAh g−1 after 100 cycles with capacity retention of 96%) and LiCoO2 (169.4 mAh g−1 after 400 cycles and with capacity retention of 95%) illustrate prominent cycling stability. This study proposes a feasible and powerful strategy for enhancing the structural stability and cycling durability of high-voltage LiCoO2 and nickel-rich ternary layered cathode materials.

Recent Progress and Regulation Strategies of Layered Materials as Cathode of Aqueous Zinc‐Ion Batteries

Aqueous zinc‐ion batteries (ZIBs) have shown great potential in the fields of wearable devices, consumer electronics, and electric vehicles due to their high level of safety, low cost, and multiple electron transfer. The layered cathode materials of ZIBs hold a stable structure during charge and discharge reactions owing to the ultrafast and straightforward (de)intercalation‐type storage mechanism of Zn2+ ions in their tunable interlayer spacing and their abilities to accommodate other guest ions or molecules. Nevertheless, the challenges of inadequate energy density, dissolution of active materials, uncontrollable byproducts, increased internal pressure, and a large de‐solvation penalty have been deemed an obstacle to the development of ZIBs. In this review, recent strategies on the structure regulation of layered materials for aqueous zinc‐ion energy storage devices are systematically summarized. Finally, critical science challenges and future outlooks are proposed to guide and promote the development of advanced cathode materials for ZIBs.

Mitigating Jahn-Teller Effect in Layered Cathode Material Via Interstitial Doping for High-Performance Sodium-Ion Batteries.

Layered transition metal oxides are promising cathode materials for sodium-ion batteries due to their high energy density and appropriate operating potential. However, the poor structural stability is a major drawback to their widespread application. To address this issue, B3+ is successfully introduced into the tetrahedral site of Na0.67 Fe0.5 Mn0.5 O2 , demonstrating the effectiveness of small-radius ion doping in improving electrochemical performance. The obtained Na0.67 Fe0.5 Mn0.5 B0.04 O2 exhibits excellent cycling performance with 88.8% capacity retention after 100 cycles at 1 C and prominent rate performance. The structure-property relationship is constructed subsequently by neutron powder diffraction, in situ X-ray diffraction and X-ray absorption spectroscopy, which reveal that the Jahn-Teller distortion and the consequent P2-P2' phase transformation are effectively mitigated because of the occupancy of B3+ at the interstitial site. Furthermore, it is found that the transition metal layers are stabilized and the transition metal dissolution are suppressed, resulting in excellent cycling performance. Besides, the prominent rate performance is attributed to the enhanced diffusion kinetics associated with the rearrangement of Na+ . This work provides novel insight into the action mechanism of interstitial site doping and demonstrates a universal approach to improve the electrochemical properties of P2-type manganese-based sodium cathode materials.

Zinc-Doping Strategy on P2-Type Mn-Based Layered Oxide Cathode for High-Performance Potassium-ion Batteries.

Mn-based layered oxide is extensively investigated as a promising cathode material for potassium-ion batteries due to its high theoretical capacity and natural abundance of manganese. However, the Jahn-Teller distortion caused by high-spin Mn3+ (t2g 3 eg 1 ) destabilizes the host structure and reduces the cycling stability. Here, K0.02 Na0.55 Mn0.70 Ni0.25 Zn0.05 O2 (denoted as KNMNO-Z) isreported to inhibit the Jahn-Teller effect and reduce the irreversible phase transition. Through the implementation of a Zn-doping strategy, higher Mn valence isachieved in the KNMNO-Z electrode, resulting in a reduction of Mn3+ amount and subsequently leading to an improvement in cyclic stability. Specifically, after 1000 cycles, a high retention rate of 97% isobserved. Density functional theory calculations reveals that low-valence Zn2+ ions substituting the transition metal position of Mn regulated the electronic structure around the MnO bonding, thereby alleviating the anisotropic coupling between oxidized O2- and Mn4+ and improving the structural stability. K0.02 Na0.55 Mn0.70 Ni0.25 Zn0.05 O2 provided an initial discharge capacity of 57 mAh g-1 at 100mA g-1 and a decay rate of only 0.003% per cycle, indicating that the Zn-doped strategy is effective for developing high-performance Mn-based layered oxide cathode materials in PIBs.

Simple Synchronous Dual-Modification Strategy with Zr4+ Doping and CeO2 Nanowelding to Stabilize Layered Ni-Rich Cathode Materials

A Ni-rich layered oxide, one promising cathode for lithium-ion batteries (LIBs), exhibits the advantages of low cost and high capacity but suffers from rapid capacity loss due to bulk structural instability and surface side reactions. Herein, a simple synchronous dual-modification strategy with Zr4+ doping and CeO2 nanowelding is proposed to address such issues. Utilizing the migration energy difference of Zr and Ce ions in layered structures, one-step high-temperature sintering of LiNi0.8Co0.1Mn0.1O2 particles with Zr and Ce nitrate distributions enables simultaneous doping of Zr ions in the bulk and CeO2 surface modification. Therein, Zr ions in the bulk occupying the Li sites can improve the Li+ diffusion rate and stabilize the crystal structure, while CeO2 on the surface provides nanowelding between the grain boundaries and resistance to electrolyte erosion. Theoretical calculations and a series of structure/composition characterizations (i.e., neutron scattering, in situ X-ray diffraction, etc.) validated the proposed strategy and its role in stabilizing the Ni-rich cathodes. The synergistic effect of Zr4+ doping and CeO2 nanowelding enables an impressive initial capacity of 187.2 mAh g–1 (2.7–4.3 V vs Li/Li+) with 86.1% retention after 200 cycles at 1 C and rate capabilities of 146.6 and 127.3 mAh g–1 at 5 and 10 C, respectively. Upon increasing the testing temperature to 60 °C, the dual-modified Ni-rich cathode exhibits an initial discharge capacity of 203.5 mAh g–1 with a good retention of 80.8% after 100 cycles at 0.5 C. The present strategy utilizing the migration energy difference of metal ions to achieve synchronous bulk doping and surface modification will offer fresh insights to stabilize layered cathode materials for LIBs, which can be widely used in other kinds of batteries with various cathode materials.

Booster Adhesion of Crystalline Poly(vinylidene fluoride) Binder by Heat Treatment for Ni‐rich Layered Oxide Cathode in Lithium‐ion Batteries

AbstractHigh energy density of lithium‐ion batteries is crucial for highly efficient battery systems. Ni‐rich layered oxide cathode materials with a high specific capacity have garnered considerable interest. Ni‐rich cathode materials exhibit rather large volume fluctuations during charging and discharging, unlike traditional cathode materials. This study investigated the electrochemical performance of a Ni‐rich cathode with a focus on controlling binder adhesion of poly(vinylidene fluoride) (PVDF), which is the most feasible cathode binder for battery manufacturing, to mitigate the failure mode of volume changes. A simple heat treatment of 200 °C over melting point is effective to enhance binding force by altering nanoscale alignment of PVDF. The study evaluates the electrochemical properties of the Ni‐rich cathode with different levels of binder adhesion to determine the optimal binder conditions for high performance.

Understanding the Insight Mechanism of Chemical-Mechanical Degradation of Layered Co-Free Ni-Rich Cathode Materials: A Review.

Layered Cobalt (Co)-free Nickel (Ni)-rich cathode materials have attracted much attention due to their high energy density and low cost. Still, their further development is hampered by material instability caused by the chemical/mechanical degradation of the material. Although there are numerous doping and modification approaches to improve the stability of layered cathode materials, these approaches are still in the laboratory stage and require further research before commercial application. To fully exploit the potential of layered cathode materials, a more comprehensive theoretical understanding of the underlying issues is necessary, along with active exploration of previously unrevealed mechanisms. This paper presents the phase transition mechanism of Co-free Ni-rich cathode materials, the existing problems, and the state-of-the-art characterization tools employed to study the phase transition. The causes of crystal structure degradation, interfacial instability, and mechanical degradation are elaborated, from the material's crystal structure to its phase transition and atomic orbital splitting. By organizing and summarizing these mechanisms, this paper aims to establish connections among common research problems and to identify future research priorities, thereby facilitating the rapid development of Co-free Ni-rich materials.

Direct Observation of Dynamic Lithium Diffusion Behavior in Nickel-Rich, LiNi0.8Mn0.1Co0.1O2 (NMC811) Cathodes Using Operando Muon Spectroscopy.

Ni-rich layered oxide cathode materials such as LiNi0.8Mn0.1Co0.1O2 (NMC811) are widely tipped as the next-generation cathodes for lithium-ion batteries. The NMC class offers high capacities but suffers an irreversible first cycle capacity loss, a result of slow Li+ diffusion kinetics at a low state of charge. Understanding the origin of these kinetic hindrances to Li+ mobility inside the cathode is vital to negate the first cycle capacity loss in future materials design. Here, we report on the development of operando muon spectroscopy (μSR) to probe the Å-length scale Li+ ion diffusion in NMC811 during its first cycle and how this can be compared to electrochemical impedance spectroscopy (EIS) and the galvanostatic intermittent titration technique (GITT). Volume-averaged muon implantation enables measurements that are largely unaffected by interface/surface effects, thus providing a specific characterization of the fundamental bulk properties to complement surface-dominated electrochemical methods. First cycle measurements show that the bulk Li+ mobility is less affected than the surface Li+ mobility at full depth of discharge, indicating that sluggish surface diffusion is the likely cause of first cycle irreversible capacity loss. Additionally, we demonstrate that trends in the nuclear field distribution width of the implanted muons during cycling correlate with those observed in differential capacity, suggesting the sensitivity of this μSR parameter to structural changes during cycling.

Unlocking high-rate O3 layered oxide cathode for Na-ion batteries via ion migration path modulation

O3-NaNi1/3Fe1/3Mn1/3O2 is a promising layered cathode material with high specific capacity, low cost, and simple synthesis. However, sluggish kinetic hindrance is attributed to the size discrepancy between the large Na-ion and narrow tetrahedral interstitial positions, leading to inferior rate capacity and low reversible capacity. Herein, F− with light‐weight and strong electronegativity is introduced to substitute O atoms in the bulk structure, which intensifies the bond strength of transition metal and oxygen and enlarges the Na+ diffusion channel. In addition, density-functional theory (DFT) calculations demonstrate that the electrostatic interaction is weakened between Na+ in the tetrahedral site and the transition-metal cation directly below it, dramatically reducing the migration barriers of Na+ diffusion. Consequently, the as-obtained NaNi1/3Fe1/3Mn1/3O1.95F0.05 sample displays outstanding rate performance of 86.7 mA h g−1 at 10 C and excellent capacity retention of 84.1% after 100 cycles at 2 C. Moreover, a full cell configuration using a hard carbon anode reaches the energy density of 307.7 Wh kg−1. This strategy paves the way for novel means of modulating the Na-ion migration path for high-rate O3-type layered cathode materials.

Direct Solution-calcination synthesis of residual Li-free layered cathode materials for Li-ion batteries

Layered cathode materials have advanced existing Li-ion batteries by improving cell voltage and enabling facile charge transfer. Yet diverse synthetic issues such as particle inhomogeneity, Li residues, complicated processes, and large micron-scale particle sizes, need to be addressed. We report a direct solution-calcination strategy for the simple and scalable synthesis of layered cathode materials (i.e. LiCoO2) for Li-ion batteries. Polyvinylpyrrolidone (PVP) as functional agent is introduced to intimately bind and uniformize the metal precursors, thereby sufficiently eliminating surface Li residues and forming a uniform particle distribution. Compared with commercial LCO, solution-calcined LCO exhibits improved cycling stability and rate capability with suppressed phase transition. The structural phase evolution mechanism for solution-calcination is investigated using in-situ X-ray diffraction analysis. Overall, our research suggests a simple and versatile strategy for the synthesis of cathode materials; the proposed method is effective and avoids complicated synthesis steps and the formation of unwanted residual lithium compounds.

High Cycling Rate‐Induced Irreversible TMO6 Slabs Glide in Co‐Free High‐Ni Layered Cathode Materials

AbstractCo‐free high‐Ni layered transition metal oxide is a promising cost‐effective cathode material for high‐energy Li‐ion batteries, but it suffers from undesirable rate performance and rapid capacity decay upon high‐rate cycling. The underlying structural changes under fast electrochemical processes remain unclear to date. In this study, atomic scale structural evolutions of Co‐free high‐Ni layered cathode at different cycling rates are revealed by advanced TEM characterization. It is found that the phase transition after high‐rate cycling is much different from that after low‐rate cycling. The low‐rate cycled sample shows a typical layer‐to‐rock salt transition. However, O1‐type stacking faults are uncovered in the high‐rate cycled sample owing to irreversible TMO6 slabs glide, which induces severe lattice distortion and structural dislocations. These findings deepen the understanding of the rate‐dependent structural degradation mechanism of Co‐free high‐Ni layered cathodes, and have significant implications for improving current materials to withstand high‐rate applications.

Preparation of layered Ni-rich LiNi0.9Co0.05Mn0.05O2 cathode materials with excellent electrochemical properties by controllable lithium supply and sintering

Layered Ni-rich cathode materials (LiNixCoyMn1-x-yO2) are promising cathode materials for next-generation lithium-ion batteries due to their high reversible capacity and energy density. However, it is still facing the challenges in unstable structure and weak electrochemical properties, inhibiting their large-scale application. Herein, Ni-rich LiNi0.9Co0.05Mn0.05O2 cathode materials are synthesized using Ni0.9Co0.05Mn0.05(OH)2 precursors and Li source by two-steps heating treatment processes. Their structure and properties are regulated by controlling Li supply amounts and sintering temperature to further expand the applications of Ni-rich cathode materials. Experimental results suggest that the preheating at 500 °C effectively establishes a structural foundation (R-3m) for the following sintering of LiNi0.9Co0.05Mn0.05O2 materials. Furthermore, it is found that Li supply amount and sintering temperature have a certain correlation with the structural stability and electrochemical properties of materials. At Li supply amount 1.04 (Li/transition metals atom ratio) and sintering temperature 700 °C, the prepared LiNi0.9Co0.05Mn0.05O2 materials exhibit optimal electrochemical properties (77.0 % capacity retention after 400 cycles at 1C, and about 128.0 mAh g‐1 discharge capacity at 10C). This study provides a rational regulating strategy for synthesizing Ni-rich LiNi0.9Co0.05Mn0.05O2 cathode materials with controllable structural and electrochemical properties, further expanding their applications in the fields of smart grids and electric vehicles.

Stacking Order Induced Anion Redox Regulation for Layer-Structured Na0.75 Li0.2 Mn0.7 Cu0.1 O2 Cathode Materials.

Stacking order plays a key role in defining the electrochemical behavior and structural stability of layer-structured cathode materials. However, the detailed effects of stacking order on anionic redox in layer-structured cathode materials have not been investigated specifically and are still unrevealed. Herein, two layered cathodes with the same chemical formula but different stacking orders: P2-Na0.75 Li0.2 Mn0.7 Cu0.1 O2 (P2-LMC) and P3-Na0.75 Li0.2 Mn0.7 Cu0.1 O2 (P3-LMC) are compared. It is found that P3 stacking order is beneficial to improve the oxygen redox reversibility compared with P2 stacking order. By using synchrotron hard and soft X-ray absorption spectroscopies, three redox couples of Cu2+ /Cu3+ , Mn3.5+ /Mn4+ , and O2- /O- are revealed to contribute charge compensation in P3 structure simultaneously, and two redox couples of Cu2+ /Cu3+ and O2- /O- are more reversible than those in P2-LMC due to the higher electronic densities in Cu 3d and O 2p orbitals in P3-LMC. In situ X-ray diffraction reveals that P3-LMC exhibits higher structural reversibility during charge and discharge than P2-LMC, even at 5C rate. As a result, P3-LMC delivers a high reversible capacity of 190.3 mAh g-1 and capacity retention of 125.7 mAh g-1 over 100 cycles. These findings provide new insight into oxygen-redox-involved layered cathode materials for SIBs.

Event-Triggered Optimal Control for Temperature Field of Roller Kiln Based on Adaptive Dynamic Programming.

Temperature field control is crucial for the comprehensive performance of Ni-Co-Mn layered cathode material that is the most important part of lithium-ion batteries. Starting from the aspect of a class of distributed parameter systems described by highly dissipative partial differential equations (PDEs), an event-triggered optimal control (ETOC) method based on adaptive dynamic programming (ADP) for the roller kiln temperature field is proposed. First, we formulate the event-triggered control problem of the temperature field under the general framework of PDE systems. Then, an event-triggered condition is designed based on the stability of the closed-loop PDE system, which also guarantees the upper bound of the performance index. Subsequently, ADP technology is adopted to realize the ETOC, where the critic network is employed to approximate the optimal value function. Since the studied system can be regarded as an impulsive dynamic system with flow dynamics and jump dynamics simultaneously, the stability of the impulsive dynamic system combined with the ADP-based closed-loop PDE system is proved. Finally, simulation results on the temperature field verify the effectiveness of the proposed method.

Molten Salt‐Assisted Synthesis of Single‐Crystalline Nonstoichiometric Li1+xNi1–xO2 with Improved Structural Stability

AbstractCobalt‐free LiNiO2 is an attractive cathode material with high energy density and low cost but suffers from severe structural degradation and poor performance. Here, a molten salt‐assisted synthesis combined with a Li‐refeeding strategy is proposed to obtain nonstoichiometric Li1+xNi1‐xO2 with submicron particle size and superior rate performance. The slightly Li‐rich and single‐crystalline characters inhibit Li+/Ni2+ anti‐site defects and mitigates the undesirable phase evolution. Remarkably, single‐crystalline Li1.045Ni0.955O2 exhibits a high specific capacity (218.7 mAh g−1 at 0.1 C), considerable rate capability (187.0 mAh g−1 at 5 C), and an initial Coulombic efficiency (89.62% at 0.1 C) in the 1.27 Ah pouch full cell employing the graphite anode, significantly outperforming near stoichiometric LiNiO2. Furthermore, the particulate morphology of Li1.045Ni0.955O2 remains intact at charge voltages up to 4.8 V, whereas near stoichiometric LiNiO2 features intragranular cracks and irreversible lattice distortion. This study underscores the value of molten salt‐assisted synthesis and Li‐refeeding modification to upgrade Ni‐based layered oxide cathode materials for advanced Li‐ion batteries.

Predicting the Lithium-Vacancy Arrangements of Layered Cathode Materials by a Voronoi Finite Element Method

We proposed a Voronoi finite element (VFE) method to determine the possible intermediate phases of cathode materials of Li-ion batteries (LIBs). Lithium-vacancy arrangements can be accurately predicted based on Voronoi polyhedra centered on lithium ions. Using this method, we can reproduce the well-known lithium removal processes of LiCoO2 and Li1.2Mn0.54Ni0.13Co0.13O2. Moreover, this method can effectively reduce the number of arrangements that need to be calculated. Our work provides a reasonable and efficient way to investigate the structural evolution of cathode materials during delithiation.