Lithium-rich Layered Cathode Research Articles

Origin of enhanced electrochemical performance in lithium-rich cathode materials via the fast ion conductor Li2O-B2O3-LiBr

Lithium-rich cathode materials have garnered significant attention in the energy sector due to their high specific capacity. However, severe capacity degradation impedes their large-scale application. The employment of fast ion conductors for coating has shown potential in improving their electrochemical performance, yet the structural and chemical mechanisms underlying this improvement remain unclear. In this study, we systematically analyze, through first-principles calculations, the mechanism by which Li2O-B2O3-LiBr (Hereafter referred to as LBB) coating enhances the electrochemical performance of the lithium-rich layered cathode material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 (Hereafter referred to as OLO). Our calculations reveal that the LBB coating introduces a more negative valence charge (average −0.14 e) around the oxygen atoms surrounding transition metals, thereby strengthening metal-oxygen interactions. This interaction mitigates irreversible oxygen oxidation caused by anionic redox reactions under high voltages, reducing irreversible structural changes during battery operation. Furthermore, while the migration barrier for Li+ in OLO is 0.61 eV, the LBB coating acts as a rapid conduit during the Li+ deintercalation process, reducing the migration barrier to 0.32 eV and slightly lowering the internal migration barrier within OLO to 0.43 eV. Calculations of binding energies to electrolyte byproducts HF before and after coating (at −7.421 and −3.253 eV, respectively) demonstrate that the LBB coating effectively resists HF corrosion. Subsequent electrochemical performance studies corroborated these findings. The OLO cathode with a 2% LBB coating exhibited a discharge capacity of 157.12 mAh g−1 after 100 cycles, with a capacity retention rate of 80.38%, whereas the uncoated OLO displayed only 141.67 mAh g−1 and a 72.45% capacity retention. At a 2 C rate, with the 2 wt% LBB-coated sample maintaining a discharge capacity of 140.22 mAh g−1 compared to only 107.02 mAh g−1 for the uncoated OLO.

Electrochemomechanical failure in layered oxide cathodes caused by rotational stacking faults.

Electrochemomechanical degradation is one of the most common causes of capacity deterioration in high-energy-density cathodes, particularly intercalation-based layered oxides. Here we reveal the presence of rotational stacking faults (RSFs) in layered lithium transition-metal oxides, arising from specific stacking sequences at different angles, and demonstrate their critical role in determining structural/electrochemical stability. Our combined experiments and calculations show that RSFs facilitate oxygen dimerization and transition-metal migration in layered oxides, fostering microcrack nucleation/propagation concurrently with cumulative electrochemomechanical degradation on cycling. We further show that thermal defect annihilation as a potential solution can suppress RSFs, reducing microcracks and enhancing cyclability in lithium-rich layered cathodes. The common but previously overlooked occurrence of RSFs suggests a new synthesis guideline of high-energy-density layered oxide cathodes.

Stabilizing the Reversible Oxygen Redox Reactions in Lithium-Rich Layered Cathodes Via the Surface-to-Bulk Enhanced D-P Hybridization

The oxygen redox (OR) reaction in layered Li-rich oxide (LLO) cathode materials has been an attractive topic as it provides additional capacity. However, the suppression of the irreversible transition metal (TM) migration and oxygen release induced by the OR reaction is still a challenging issue, as it would lead to a severe capacity and voltage decay. Here, we introduce a surface-to-bulk structure modification strategy, namely surface Ni segregation and bulk Mo doping structure. Based on this strategy, the oxygen atoms near the surface are fully coordinated, and meanwhile the distortion of the metal–oxygen octahedron is alleviated in the bulk phase, thereby enhancing the degree of TM 3d and O 2p hybridization to stabilize the metal–oxygen framework for the OR reaction. It suppresses cation migration and oxygen release and maintains phase stability, allowing a reversible OR reaction. As a result, the capacity and voltage retention of the modified materials were significantly improved. This work gives an efficient method to stabilize the OR reaction through the surface-to-bulk enhanced d-p hybridization and provides new paths for the design of Li-rich cathodes.

Surface engineering of Li1.5Ni0.25Mn0.75O2.5 cathode material using TiO2 nanoparticles: An approach to improve electrochemical performance and thermal stability

Lithium-rich layered cathode materials have drawn great attention in lithium-ion cells owing to their high theoretical specific capacity and high working voltage. In this study, a lithium-rich layered cathode, Li1.5Ni0.25Mn0.75O2.5 (LNMO) is synthesized by a carbonate co-precipitation method and further coated with bio-synthesized TiO2 nanoparticles. The effect of nano-TiO2 coating on the electrochemical performance and thermal stability was thoroughly studied. The results reveal that the 2 wt% TiO2-coated sample shows excellent capacity retention (∼89.3% capacity retention at 1 C rate after 200 cycles) whereas, the pristine LNMO shows severe capacity fading (only 78.4% capacity retained after 100 cycles at 1 C) and voltage decay. The coated sample also exhibits superior rate performance than the pristine sample (181.6 mAh g−1 for 2 wt% TiO2-coated LNMO and 113.3 mAh g−1 for pristine LNMO, at 2 C). Moreover, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analyses demonstrate the enhanced thermal stability of the 2 wt% TiO2-coated sample under charged condition.

Opportunities and Challenges of Layered Lithium-Rich Manganese-Based Cathode Materials for High Energy Density Lithium-Ion Batteries

Opportunities and Challenges of Layered Lithium-Rich Manganese-Based Cathode Materials for High Energy Density Lithium-Ion Batteries

Computational Understandings of Cation Configuration-Dependent Redox Activity and Oxygen Dimerization in Lithium-Rich Manganese-Based Layered Cathodes

Lithium-rich manganese-based layered oxides have emerged as a fresh paradigm for developing advanced cathode materials with high energy density for next-generation lithium-ion batteries. Understanding lattice oxygen dimerization is quite essential for the optimal design of lithium-rich manganese-based cathode materials. Herein, based on density functional theory (DFT) calculations, a local Ni-honeycomb Li–Ni–Mn cation configuration for the Li1.22Ni0.22Mn0.56O2 cathode was carefully examined, which may coexist with the well-known local Li-honeycomb structure in experimentally synthesized Li1.2Ni0.2Mn0.6O2 samples. The local Li–Ni–Mn cation configurations have significant impacts on oxygen redox activity, transition metal atom migration, and oxygen dimerization in the charging process of LixNi0.22Mn0.56O2. It is found that there is no correlation between high lattice oxygen redox activity and easy oxygen dimerization, such as Li-honeycomb structures simultaneously exhibiting higher oxygen redox activities and higher activation energy barriers for prohibiting oxygen dimerization than Ni-honeycomb structures. The structural regulations of the local Li–Ni–Mn cation configuration by avoiding the local Ni-honeycomb structures to inhibit Mn migration and ease lattice oxygen dimerization and by making full use of the local Li-honeycomb structures would maximize performance of Li-rich Mn-based layered oxides. Such fresh insights provide us a fresh strategy to optimally design the local honeycomb structure for high-performance Li-rich Mn-based cathode materials.

Constructing uniform oxygen defect engineering on primary particle level for high-stability lithium-rich cathode materials

Lithium-rich layered cathode materials are considered to be research focus of cathode candidates for next-generation lithium-ion batteries due to their high specific capacity and low cost. However, lattice deoxidation associated with elemental migration and internal local shrinkage usually results in deteriorated cyclic performance and notorious voltage attenuation, severely limiting its application. In this paper, we have successfully injected uniform oxygen defects into surface region of Li1.2Ni0.13Co0.13Mn0.54O2 primary particles under the high-pressure and weak carbonate environment. Various experimental investigations indicate that the injected robust oxygen defects can not only mitigate detrimental interfacial reactions but also suppress unfavorable lattice variation and particle breakage. More importantly, theoretical calculations unravel the critical roles of oxygen defects in regulating energy band structure for strengthened anionic reversibility. Owing to stabilization effects of unique oxygen defect engineering, the modified Li1.2Ni0.13Co0.13Mn0.54O2 cathode has harvested dramatically enhanced electrochemical performance including a high initial coulombic efficiency of 96.6%, an outstanding capacity retention of 91.96% (1C, 200 cycles) and suppressed voltage decay of only 1.62 mV per cycle. Therefore, this facile and effective defect engineering strategy could establish new guidance for promoting practical application of Li-rich Mn-based cathode material.

Mitigated lattice distortion and oxygen loss of Li-rich layered cathode materials through anion/cation regulation by Ti4+-substitution

Lithium-rich layered cathode material (LLM) can meet the requirement of power lithium-ion energy storage devices due to the great energy density. However, the de/intercalation of Li+ will cause the irreversible loss of lattice oxygen and trigger transition metal (TM) ions migrate to Li+ vacancies, resulting in capacity decay. Here we brought Ti4+ in substitution of TM ions in Li1.2Mn0.54Ni0.13Co0.13O2, which could stabilize structure and expand the layer spacing of LLM. Moreover, optimized Ti-substitution can regulate the anions and cations of LLM, enhance the interaction with lattice oxygen, increase Ni3+ and Co3+, and improve Mn4+ coordination, improving reversibility of oxygen redox activation, maintaining the stable framework and facilitating the Li+ diffusion. Furthermore, we found 5% Ti-substitution sample delivered a high discharge capacity of 244.2 mAh/g at 50 mA/g, an improved cycling stability to 87.3% after 100 cycles and enhanced rate performance. Thereby Ti-substitution gives a new pathway to achieve high reversible cycle retention for LLMs.

On the disparity in reporting Li-rich layered oxide cathode materials.

Lithium-rich layered oxides are considered one of the most promising cathode materials for next generation lithium-ion batteries due to their extraordinary specific capacity of over 280 mA h g-1 and superior energy density of over 1000 W h kg-1. Despite the excellent performance, LRLOs still suffer from low Coulombic efficiency, serious capacity/voltage decay upon cycling, voltage hysteresis, short lifespan, and poor rate capability. Driven by the thirst for high-energy-density battery technologies, various strategies have been developed to address these issues with great progress being achieved in the past several years. However, the emerging disparity among the published results severely precludes meaningful comparisons between different LRLOs and material modification strategies, which has become an impediment to the development and commercialization of LRLOs. Although the significance of standardization has been recognized in the battery community, the standardization of LRLOs is worth particular attention due to their complicated compositions and unique electrochemical properties. This perspective analyzes the underlying parameters that can cause varied and even controversial results observed in LRLOs, from the synthesis procedure to the electrochemical evaluation procedure, followed by preliminary suggestions for the standard protocols of chemical compositions, synthesis pathways, calcination conditions, electrode preparation, battery fabrication, and battery testing. Hopefully, this perspective can help build a reliable baseline for LRLO research, thus aligning the huge research effort toward the practical applications of LRLOs.

Progress on Modification Strategies of Layered Lithium-Rich Cathode Materials for High Energy Lithium-Ion Batteries

Progress on Modification Strategies of Layered Lithium-Rich Cathode Materials for High Energy Lithium-Ion Batteries

In2O3 surface modification of a Li-rich layered cathode material for boosting electrochemical performance

Lithium-rich layered cathode materials have high specific capacities. However, some drawbacks such as low initial Coulombic efficiency (ICE) and severe capacity/voltage decay during repeated cycling hinder their practical applications. Herein, a pristine Li1.2Mn0.54Ni0.13Co0.13O2 (LMNCO) material is synthesized by the carbonate coprecipitation method and then the In2O3 surface modified LMNCO materials with different amounts of In2O3 are prepared by the facile solvent evaporation and calcination method. The In2O3-modified LMNCO material with 2 wt% In2O3 demonstrates the highest ICE and the best rate capability and cycle stability, which are much superior to those of the pristine LMNCO. This surface modified material exhibits the specific capacities of 268.2 and 109.1 mAh g−1 at the current rates of 0.1C and 5C, respectively. After cycling at 1C rate for 200 cycles, the discharge specific capacity is declined from 176.2 to 140.9 mAh g−1, giving capacity retention of 80.0%. The improved electrochemical performance is ascribed to the surface modification of a moderate amount of In2O3. This surface modification can enhance the electrical conduction and hence the electrochemical reaction activity of the active material without hindering the lithium ion transport through the electrode surface. Moreover, it can suppress the undesirable increasing growing of the solid electrolyte interphase film during the repeated charge/discharge cycling due to the surface side reactions between the active material and the electrolyte.

Heterostructured lithium-rich layered oxides core@ spinel- MgAl2O4 shell as high-performance cathode for lithium-ion batteries

Lithium-rich layered oxides (LLO) with ultra-high specific capacity are one of the most promising cathodes for the next-generation lithium-ion batteries. However, the irreversible release of lattice oxygen will cause LLO surface reconstruction and electrolyte decomposition, resulting in low initial coulombic efficiency (ICE), high interface resistance as well as severe voltage and capacity degradation. Herein, a facile and effective strategy is proposed to stabilize the cathode materials by coating the LLO with spinel MgAl2O4. It is found that the robust MgAl2O4 (MAO) decoration layer can not only alleviate the lattice mismatch to sustain the structure integrity, but also inhibit the side reactions with electrolyte during long-term cycles. Furthermore, density functional theory calculations show that the surface oxygen release energy barrier is increased with the surface decoration of MAO. Accordingly, the coated LLO-based hetero-structured cathode exhibits a higher ICE (80.14%) and lower interface resistance than that of LLO electrode. Moreover, a reversible capacity of 176.6 mAh g−1 (with a capacity retention as high as 78.1%) and small voltage drop of 0.27 V are achieved even after 200 cycles at 1 C. This work sheds new light on the facile preparation and modification of lithium-rich layered oxides-related cathode for high-energy density lithium-ion batteries.

Significant Enhancement of the Capacity and Cycling Stability of Lithium-Rich Manganese-Based Layered Cathode Materials via Molybdenum Surface Modification.

Lithium-rich manganese-based layered cathode materials are considered to be one of the best options for next-generation lithium-ion batteries, owing to their ultra-high specific capacity (>250 mAh·g−1) and platform voltage. However, their poor cycling stability, caused by the release of lattice oxygen as well as the electrode/electrolyte side reactions accompanying complex phase transformation, makes it difficult to use this material in practical applications. In this work, we suggest a molybdenum surface modification strategy to improve the electrochemical performance of Li1.2Mn0.54Ni0.13Co0.13O2. The Mo-modified Li1.2Mn0.54Ni0.13Co0.13O2 material exhibits an enhanced discharge specific capacity of up to 290.5 mAh·g−1 (20 mA·g−1) and a capacity retention rate of 82% (300 cycles at 200 mA·g−1), compared with 261.2 mAh·g−1 and a 70% retention rate for the material without Mo modification. The significantly enhanced performance of the modified material can be ascribed to the formation of a Mo-compound-involved nanolayer on the surface of the materials, which effectively lessens the electrolyte corrosion of the cathode, as well as the activation of Mo6+ towards Ni2+/Ni4+ redox couples and the pre-activation of a Mo compound. This study offers a facile and effective strategy to address the poor cyclability of lithium-rich manganese-based layered cathode materials.

Improving the oxygen redox reversibility of Li-rich battery cathode materials via Coulombic repulsive interactions strategy

The oxygen redox reaction in lithium-rich layered oxide battery cathode materials generates extra capacity at high cell voltages (i.e., >4.5 V). However, the irreversible oxygen release causes transition metal (TM) dissolution, migration and cell voltage decay. To circumvent these issues, we introduce a strategy for tuning the Coulombic interactions in a model Li-rich positive electrode active material, i.e., Li1.2Mn0.6Ni0.2O2. In particular, we tune the Coulombic repulsive interactions to obtain an adaptable crystal structure that enables the reversible distortion of TMO6 octahedron and mitigates TM dissolution and migration. Moreover, this strategy hinders the irreversible release of oxygen and other parasitic reactions (e.g., electrolyte decomposition) commonly occurring at high voltages. When tested in non-aqueous coin cell configuration, the modified Li-rich cathode material, combined with a Li metal anode, enables a stable cell discharge capacity of about 240 mAh g−1 for 120 cycles at 50 mA g−1 and a slower voltage decay compared to the unmodified Li1.2Mn0.6Ni0.2O2.

Modulating anionic activities in layered Li-rich cathode materials with inverse spinel MnFe2O4 coating

Layered Li-rich cathode oxides can provide high specific capacity due to oxygen anion redox involving in charge compensation process during cycling, but there is a severe structural transition from layered to spinel accompanying with irreversible oxygen loss during cycling, which lead to electrochemical degradation. The current researches show that the irreversible oxygen evolution reaction of layered lithiumrich materials in the first cycle mainly comes from the surface lattice oxygen, so the surface modification by the materials with more stable structure is one of the effective ways to improve the electrochemical performance of layered lithium-rich materials. In this paper, we report a modified layered lithium-rich cathode material by surface coating of inverse spinel MnFe2O4. The inverse spinel has strong polarization effect on anion migration due to its different atoms occupying octahedral sites from layered structure and it can also modulate the Fermi level and stretching the O-O bond, thereby increasing the energy barrier for surface oxygen oxidization. Furthermore, the three-dimensional connected tunnel structure of the inverse spinel also makes the surface layer of the material have a faster lithium ion transferring rate, and a large number of lithium storable vacancies inside of it improved the Li+ intercalation efficiency, initial coulombic efficiency and rate performance. Compared with the unmodified sample, the modified material coated with 2% MnFe2O4 has superior cycle stability and outstanding rate performance. It is hoped our work would provide the knowledge for the future development of high-performance cathode materials for Li-ion batteries.

Density functional theory guidance on rare earth doping—inhibition of lattice oxygen evolution in lithium-rich layered manganese oxide materials

Lithium-rich manganese layered oxide (LLMO) materials are one of the key materials for high energy density lithium ion batteries, but the loss of lattice oxygen during cycling leads to the increase of lithium ion transport resistance and the deterioration of material properties. In this study, density functional theory is used to calculate the formation energies and doping sites of 13 rare earth-doped LLMOs. Rare earth elements tend to occupy the Co site in the LiMO2 phase and screen out Yb, Lu, etc. as the higher-order dopant. The theoretical screening is verified by synthesizing Li1.2Ni0.133Co0.123Mn0.533RE0.01O2 (RE= La, Ce, Nd, Eu, Tm, Yb and Lu) cathode materials. Compared with undoped materials, the doping effect of heavy rare earth elements is better than that of light rare earth elements, which is consistent with the calculation results. Among them, Yb doping has the lowest formation energy, which enhances the TM-O hybridization. The evolution of lattice oxygen is significantly reduced and the material exhibits excellent electrochemical performance (the first discharge capacity is as high as 342.5 mAh g−1). These results provide a reference for the preparation of rare earth doped lithium-rich layered cathode materials with high capacity and stability.

Na doping into Li-rich layered single crystal nanoparticles for high-performance lithium-ion batteries cathodes

Lithium-rich layered manganese-based cathodes (LRLMOs) with first-class energy density (∼1000 W h kg−1) have attracted wide attention. Nevertheless, the weak cycle stability and bad rate capability obstruct their large-scale commercial application. Here, single crystal Li1.2−x Na x Ni0.2Mn0.6O2 (x = 0, 0.05, 0.1, 0.15) nanoparticles are designed and successfully synthesized due to the single crystal structure with smaller internal stress and larger ionic radius of Na. The synergistic advantages of single crystal structure and Na doping are authenticated as cathodes for Li ion batteries (LIBs), which can consolidate the crystallographic structure and be benefit for migration of lithium ion. Among all the Na doping single crystals, Li1.1Na0.1Ni0.2Mn0.6O2 cathode possesses supreme cycling life and discharge capacity at large current density. To be more specific, it exhibits a discharge capacity of 264.2 mAh g–1 after 50 charge and discharge cycles, higher than that of undoped material (214.9 mAh g–1). The discharge capacity of Li1.1Na0.1Ni0.2Mn0.6O2 cathode at 10 C (1 C = 200 mA g−1) is enhanced to 160.4 mAh g−1 (106.7 mAh g–1 for x = 0 sample). The creative strategy of Na doping single crystal LRLMOs might furnish an idea to create cathode materials with high energy and power density for next generation LIBs.

(Invited) Reaction Mechanism of Lithium-Rich Layered Cathode Materials in Thin-Film Solid-State Battery

Lithium excess layered cathode materials are a promising cathode candidate because the higher discharge capacity. Among them, Li2MnO3 has the highest Li content and understanding the reaction mechanism during cycling is critical for using the material. We fabricated the cathode films and studied the reaction mechanisms by in-situ and methods using surface X-ray diffraction and operando HAXPES analyses. Experiments revealed a structural change to a high-capacity phase that proceeded gradually with cycling. First-principles calculations suggested that the activated phase has O1 stacking. We propose a mechanism: charging to a high voltage at a low Li concentration induces an irreversible transition to a phase detrimental to cycling that could, but not necessarily, be accompanied by the dissolution of Mn and/or the release of O into the electrolyte.

Reaction inhomogeneity coupling with metal rearrangement triggers electrochemical degradation in lithium-rich layered cathode

High-energy density lithium-rich layered oxides are among the most promising candidates for next-generation energy storage. Unfortunately, these materials suffer from severe electrochemical degradation that includes capacity loss and voltage decay during long-term cycling. Present research efforts are primarily focused on understanding voltage decay phenomena while origins for capacity degradation have been largely ignored. Here, we thoroughly investigate causes for electrochemical performance decline with an emphasis on capacity loss in the lithium-rich layered oxides, as well as reaction pathways and kinetics. Advanced synchrotron-based X-ray two-dimensional and three-dimensional imaging techniques are combined with spectroscopic and scattering techniques to spatially visualize the reactivity at multiple length-scales on lithium- and manganese-rich layered oxides. These methods provide direct evidence for inhomogeneous manganese reactivity and ionic nickel rearrangement. Coupling deactivated manganese with nickel migration provides sluggish reaction kinetics and induces serious structural instability in the material. Our findings provide new insights and further understanding of electrochemical degradation, which serve to facilitate cathode material design improvements.

In-situ reconstruction of spinel interface on Li-rich layered cathode with improved electrochemical performances

The produced inactive interface during the cycle and poor rate performance are the inevitable obstacles for the practicability of lithium-rich layered cathode. Here, we report that in-situ surface pretreatment technique with hydrazine hydrate can reconstruct epitaxial spinel possessing the rapid lithium ions diffusion path, which primarily includes the leaching of Li+/Ni2+ and redistribution of the metal ions. We confirm the generation of epitaxial spinel heterostructure on the layered matrix by kinds of characterization methods such as transmission electron microscopy and Raman spectroscopy. As a result, the epitaxial spinel substantially promotes the lithium ion diffusion coefficient from 1.98 × 10−11 cm2 s−1 to 3.76 × 10−11 cm2 s−1. Even under a discharge current 5 C, the reversible capacity still reaches up to 171.1 mAh g−1. After 200 cycles at 1 C, the modified cathode delivers a capacity retention of 84.2% with the discharge capacity of 197.8 mAh g−1. The presence of the epitaxial spinel layer exerts a positive effect on the stability of the cathode structure and suppression of side reactions at the interface via exploring the morphology and composition of the cycled cathodes. The in-situ surface reconstruction technology to generate spinel is appealing for promise prospect application of lithium-rich layered cathodes in the future.