Lithium-rich Layered Cathode Materials 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.

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

Study on Attenuation Mechanism of High Energy Density Lithium Rich Battery Materials

The development of lithium rich layered oxide cathode materials with high energy density is one of the keys to improve the range of new energy vehicles. However, there are two bottlenecks in the development of this material: the voltage attenuation caused by structural transformation and the drastic decomposition of electrolyte at high voltage. In this paper, spherical Li1.2Mn0.54Co0.13Ni0.13O2 cathode material (LLO) was prepared, and the cycle performance of LLO cathode in LiBOB electrolyte with different content was compared. In addition, the effect of LiBOB electrolyte additives on lithium rich layered oxide materials was investigated. The decomposition path of LiBOB and the composition of stable CEI film were inferred by using computational chemistry and a variety of surface / interface detection methods.

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.

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.

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.

(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.

Cesium-doped layered Li1.2Mn0.54Ni0.13Co0.13O2 cathodes with enhanced electrochemical performance

Lithium-rich layered cathode materials recently arouse highly attention for the high discharge capacities over conventional cathode materials, but trapped for severe voltage decay, poor cycling stability and inferior rate performance upon cycling. In this work, introducing Cs ions into the Li layer is employed to prepare Cs+-doped cathode material Li1.2Mn0.54Ni0.13Co0.13O2 via a simple sol-gel method and a subsequent calcination process. The Cs+ − doped sample exhibits much enhanced electrochemical performances in comparison with that of pristine sample, especially the rate capability (171.1 mAh g−1 compared to 150.2 mAh g−1 at 5C). Meanwhile, the Cs-doped one reaches an initial discharge capacity of 247.4 mAh g−1 with improved initial Coulombic efficiency of 86.0% at 0.2C rate and outruns for 177.9 mAh g−1 of discharge capacity after 100 cycles at 0.5C. Additionally, it is observed that the Cs+- doped sample has a well-defined layered structure and an expanded Li slab space caused by the Cs+ accommodation, which provides facile Li+ diffusion paths and reduces the energy barrier of the Li+ insertion/extraction in the crystal lattice. More importantly, the Cs doping is in favor of stabilizing the crystal structure and meanwhile restraining the decrease of discharge voltage by alleviating the phase transition of layered to spinel structure upon cycling, thus greatly contributing to the better electrochemical performances.

Enhanced electrochemical performances of cerium-doped Li-Rich Li1.2Ni0.13Co0.13Mn0.54O2 cathode materials

The effects of cerium doping and the formation of layered-spinel hetero-structure on the electrochemical properties of lithium-rich cathode material were studied. The doped sample with layered-spinel phase exhibited enhanced cycling rate capability and long-term cyclability, which achieved an initial discharge capacity of 265.4 mAh g−1 at 0.1 C and the capacity retention was 98.2% after 100 cycles at 1.0 C. The existence of layered-spinel hetero-structure in lithium-rich layered cathode material induced by cerium doping was believed to contribute to the remarkable improvement of cycling stability and rate capability. Cerium doping and the formation of spinel phase together facilitated lithium ion diffusion and inhibited the structural collapse during cycling.

Reaction Mechanisms of Layered Lithium-Rich Cathode Materials for High-Energy Lithium-Ion Batteries.

Layered lithium-rich cathode materials have attracted extensive interest owing to their high theoretical specific capacity (320-350 mA h g-1 ). However, poor cycling stability and sluggish reaction kinetics inhibit their practical applications. After many years of quiescence, interest in layered lithium-rich cathode materials is expected to revive in answer to our increasing dependence on high-energy-density lithium-ion batteries. Herein, we review recent research progress and in-depth descriptions of the structure characterization and reaction mechanisms of layered lithium-rich manganese-based cathode materials. In particular, we comprehensively summarize the proposed reaction mechanisms of both the cationic redox reaction of transition-metal ions and the anionic redox reaction of oxygen species. Finally, we discuss opportunities and challenges facing the future development of lithium-rich cathode materials for next-generation lithium-ion batteries.

Rocksalt type Li2Nb0·15Mn0·85O3 without structure degradation or redox evolution upon cycling

Voltage and capacity decay problems of Li2MnO3-based lithium rich layered cathode materials are still unsolved, which are the major barriers for its practical application. Intensive investigations of their mechanisms have been proceeded in recent years, which clarify cation ordered arrangement and spinel deterioration are culprits in structural aspect. Herein, we conduct various analyses to a rocksalt type Li2Nb0·15Mn0·85O3, whose first charge process is along with primary oxygen redox as Li2MnO3, but subsequently shows much better capacity retention. This material suffers from severe voltage decay and overpotential during the cycle but hard X-ray diffraction indicates it can remain rocksalt structure without any tendency of spinel deterioration or cation ordering even with massive lithium vacancies. XAS results further show there is no evident oxygen redox activity from the second cycle, while the redox range of Mn nearly has no change during the cycle. Our results demonstrate that disordered lithium rich cathode materials could be promising to exhibit highly reversible capacity upon long cycling, and their voltage decay problem could be easier to be solved for different mechanism from layered one.

Enhancing the Stability of Lithium-Rich Manganese-Based Layered Cathode Materials for Li-Ion Batteries Application

Enhancing the Stability of Lithium-Rich Manganese-Based Layered Cathode Materials for Li-Ion Batteries Application

The effect on the properties of each element in the Li1.2Mn0.54Ni0.13Co0.13O2 material by the incorporation of Al

In this paper, a lithium-rich layered cathode material Li1.2Mn0.54Ni0.13Co0.13O2 was synthesized by improving the sol-gel method. Lithium-rich manganese-based cathode materials are one of the promising next-generation lithium-ion battery cathode materials. However, this material has problems of severe capacity reduction and poor rate performance. By adding a certain amount of Al to replace the metal element in the raw material, and then testing and analyzing various produced materials, it was found that adding a certain amount of Al to replace the lithium element in the raw material can improve the cycle performance and stability of the material. XRD and SEM results show that the incorporation of Al does not significantly change the structure and morphology of the material. The results of electrochemical tests show that the Al-doped sample LMNCAO-1 has good specific capacity and stability. LMNCAO-1 has a high initial specific capacity of 271.0 mAh/g at a voltage of 2–4.8 V and a current density of 0.1 C. The initial discharge specific capacity of the sample LMNCAO-1 was 185 mAh/g at 0.5 C, and the cycle retention rate was 97.3% after 100 cycles.

Improved storage capability and cycle stability in a Li-riched cathode by substituted Al

A lithium-rich layered cathode material Li1.2Mn0.54Ni0.13Co0.13O2 with high specific capacity and good cycle stability was successfully synthesized by a modified sol-gel method. The Li element was replaced by Al, and Li1.16Mn0.54Ni0.13Co0.13Al0.04O2 material with better performance was obtained. Characterized and observed by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), Al substituted material not only has a good crystal structure and a layered structure but also improves structural stability. The electrochemical results show that Al-substitution Li1.16Mn0.54Ni0.13Co0.13Al0.04O2 material has good electrochemical performance. The initial discharge capacity at room temperature is 271 mAh/g in the potential range of 2.0–4.8 V at 0.1C rate. Even at high rates of 0.5C and 2C, the material provides 185 mAh/g and 156.1 mAh/g capacity, with capacity retention rates of 85.2% and 87.3% after 200 cycles, respectively. Therefore, the positive electrode material synthesized by the sol-gel method after doping Al may be an efficient method for replacing the electrode material.