Lithium-rich Cathode Materials Research Articles

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.

Study on La-doped lithium-rich manganese-based cathode materials (Li1.5Mn0.7Co0.15Ni0.15O2.5)

Study on La-doped lithium-rich manganese-based cathode materials (Li1.5Mn0.7Co0.15Ni0.15O2.5)

A facile and high-effective oxygen defect engineering for improving electrochemical performance of lithium-rich manganese-based cathode materials

The irreversible evolution of oxygen for lithium-rich manganese-based cathode (LRMC) is the main challenge which will induce accelerated migration of transition metal ions and structural transformation, thus resulting in serious voltage attenuation and capacity decay. Herein, a facile and high-effective oxygen vacancy engineering of hydrogenation treatment is proposed for introducing oxygen vacancy on the surface of LRMC to suppress the irreversible evolution of oxygen. X-ray diffraction (XRD) Rietveld refinement, X-ray photoelectron spectroscopy and electron paramagnetic spectroscopy demonstrate the successful introduction of oxygen vacancy on the surface of LRMC. The changes of physicochemical properties of LRMC after hydrogenation treatment are investigated through systematical electrochemical performance tests and scanning electron microscopy and transmission electron microscopy. The investigative results reveal that the presence of oxygen vacancy can significantly improve the structural stability, electrical conductivity and Li+ diffusion kinetics of the LRMC materials. Especially, the optimized H500-LRMC shows excellent electrochemical performances including the enhanced cyclic stability with a capacity retention of 221.8 mAh g−1 and a capacity retention rate of 94.11% after 100 cycles. Therefore, the well-designed oxygen vacancy engineering through hydrogenation treatment is a promising strategy for the development and industrialization of the high-performance LRMC.

Stabilized cobalt-free lithium-rich cathode materials with an artificial lithium fluoride coating

Stabilized cobalt-free lithium-rich cathode materials with an artificial lithium fluoride coating

Highly stable surface and structural origin for lithium-rich layered oxide cathode materials

Surface/interfacial engineering is critical for preventing particle degradation of Li-rich layered oxides (LLOs), particularly facet degradation, thereby optimizing their electrochemical performance. Thus, the current study details the investigative analysis of the surface structure of an LLO, followed by its surface engineering. The surface structure was analyzed using scanning transmission electron microscopy (STEM) and soft X-ray absorption spectroscopy (sXAS), and the electrochemical performance was evaluated. The results indicate that an integrated spinel/rock salt (ISR) surface structure formed on the surface in situ. More precisely, the spinel phase originated from the C2/m surface, whereas the rock salt phase originated from the R3m surface, which significantly increased the cycle stability and suppressed voltage decay. After 2000 cycles, the surface-modified LLO cathode retained an extremely high capacity of 69.6% and a low discharge medium voltage with a decay rate of 0.44 mV cycle−1. Additionally, the structural and morphological changes observed after prolonged cycling confirmed the stability of the surface layer. The outstanding performance was attributed to the ultra-stable ISR surface layer, the presence of multiple ion conductivities (LiPO3 and Li2SO4), and the substantial prevention of electrochemical facet degradation. The findings, therefore, highly suggest that the ISR surface concept and the method for surface modification is highly likely to aid in the rapid commercialization of LLOs for battery applications.

Effect of Na Doping on the Electrochemical Performance of Li1.2Ni0.13Co0.13Mn0.54O2 Cathode for Lithium-Ion Batteries

This study aims to investigate the effect of Na doping on the structure, electrical, and electrochemical properties of lithium-rich cathode material. Pristine Li1.2Ni0.13Mn0.54Co0.13O2 (LNMC) and Na-doped Li1.17Na0.03Ni0.13Mn0.54Co0.13O2 (Na-LNMC) layered lithium-rich/manganese-rich compounds are prepared by the sol-gel method. The structural and morphological characterization reveals that the Na doping leads to an ordered structure with regular cubic morphology and enlarged Li layer spacing. This enlargement facilitates the diffusion of lithium ion inside the bulk lattice. Electrochemical impedance spectroscopy (EIS) shows that doping by a small amount of Na (3 mol%) decreases the impedance by more than three orders of magnitude and enhances the diffusion of lithium ions in the same proportion. This remarkable improvement in the conductivity and diffusion coefficient of lithium ions of Na-LNMC improves its capacity retention. In addition, this structure and mode of preparation results in “U-shaped” capacity vs. cycle curves, similar to the curves observed for transition metal oxide electrodes, resulting in an exceptional cycle life, tested for up to 400 cycles at 2C.

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.

Improvement of electrochemical properties of lithium-rich manganese-based cathode materials by Ta2O5

Improvement of electrochemical properties of lithium-rich manganese-based cathode materials by Ta2O5

Doping and Coating Synergy to Improve the Rate Capability and Cycling Stability of Lithium-Rich Cathode Materials for Lithium-Ion Batteries

Doping and Coating Synergy to Improve the Rate Capability and Cycling Stability of Lithium-Rich Cathode Materials for Lithium-Ion Batteries

Theoretical investigations of selective cation doping as a novel design strategy for high-capacity lithium-rich cathode materials

On the route towards higher energy densities of lithium ion batteries (LIBs) for electromotive applications, the low capacity of state-of-the-art cathode materials is still a limiting factor. Lithium-rich layered oxides (LLOs), a composite of layered LiMO2 (M = Ni, Co, Mn) and Li2MnO3, are a promising material class, which exhibit high discharge capacities based on additional anionic redox activity but still suffer from oxygen release and correlated structural instability. In order to overcome these issues, which are mostly related to the Li2MnO3 parent structure, doping is a common strategy. In this study, the effects of different cation dopants on manganese and lithium sites of the Li2MnO3 structure were systematically studied using first-principles calculations based on density functional theory (DFT). By using cluster expansion methods the thermodynamically stable ground states of doped and delithiated structures were calculated. We show that the dopants have a severe influence on the delithiation process, a fact that is often neglected in theoretical studies of doped structures. Multivalent dopants on lithium sites, like Al3+ and Ti4+, have a strong effect on the electronic structure as well as on the initial redox potential of the material. Moreover, enhanced metal–oxygen bonding and a decreased oxidation of the oxygen anions during delithiation are observed which indicate a reduction of both, the irreversible release of oxygen as well as unwanted structural changes.

Approaching a stable oxygen redox reaction in lithium-rich cathode materials: structural perspectives from mechanism to optimization

We review the oxygen redox reaction in lithium-rich cathodes from structural perspectives. The structure–OR coupling, structural evolution, and efficient structural control strategies are introduced, followed by an outlook on future rational design.

Effects of Triple Modification Of Sodium Hypophosphite on Structure and Electrochemical Performances of Lithium-Rich Manganese-Based Cathode Materials

Effects of Triple Modification Of Sodium Hypophosphite on Structure and Electrochemical Performances of Lithium-Rich Manganese-Based Cathode Materials

Multi-dimensional correlation of layered Li-rich Mn-based cathode materials

Lithium-rich manganese-based cathode materials are expected to promote the commercialization of lithium-ion batteries to a new stage by virtue of their ultrahigh specific capacity and energy density advantages. However, they are still restricted by complex phase transitions and electrochemical performance degradation caused by labile anion charge compensation. A deep understanding of the electrochemical properties contained in their intrinsic structures and the key driving factors of structural deterioration during cycling are crucial to guide the preparation and optimization of lithium-rich materials. Considering recent progress, this review introduces the intrinsic properties of Li-rich manganese-based cathode materials from interatomic interactions to particle morphology at multiple scales in the spatial dimension. The charge compensation mechanism and energy band reorganization of the initial charge and discharge, the structural evolution during cycling and the electrochemical reaction kinetics of the materials are analyzed in the temporal dimension. Based on the relationship between structure and electrochemical performance, preparation methods and modification methods are introduced to guide and design cathode materials. Effective characterization methods for studying anion charge compensation behavior are also demonstrated. This review provides important guidance and suggestions for making full use of the high specific capacity in these materials derived from anion redox and the maintaining of its stability.

A Facile and High-Effective Oxygen Defect Engineering for Improving Electrochemical Performance of Lithium-Rich Manganese-Based Cathode Materials

A Facile and High-Effective Oxygen Defect Engineering for Improving Electrochemical Performance of Lithium-Rich Manganese-Based Cathode Materials

Formation of oxygen vacancies in Li-rich Mn-based cathode material Li<sub>1.167</sub>Ni<sub>0.167</sub>Co<sub>0.167</sub>Mn<sub>0.5</sub>O<sub>2</sub>

Using the first-principles method based on the density functional theory, the oxygen vacancy formations in the lithium-rich manganese-based ternary cathode material Li<sub>1.167</sub>Ni<sub>0.167</sub>Co<sub>0.167</sub>Mn<sub>0.5</sub>O<sub>2</sub> are calculated. The changes of oxygen vacancy formation energy with temperature, oxygen partial pressure and point defects in the material are discussed, meanwhile, the effect of oxygen vacancies on the capacity is also discussed. The calculation results show that the increase of temperature and the decrease of oxygen partial pressure can lead the formation energy of an oxygen vacancy to decline. For the charged oxygen vacancies (<inline-formula><tex-math id="M4">\begin{document}$ {\mathrm{V}}_{\mathrm{O}}^{+1} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M4.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M5">\begin{document}$ {\mathrm{V}}_{\mathrm{O}}^{+2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="17-20220274_M5.png"/></alternatives></inline-formula>), the formation energy of an O-vacancy increases with Fermi level increasing. It is also found that the presence of an oxygen vacancy will trigger off a very local charge density redistributions, mainly around the neighboring Mn ions next to the O-vacancy. Furthermore, the effects of point defects, including cation vacancies and substitutional defects in the vicinity of the O-vacancy, on the formation energy of O-vacancy are also calculated. The results show that the presence of Mn vacancy near the O-vacancy is beneficial to the formation of the O-vacancy. In addition, the formation of oxygen vacancy is suppressed when the Mn atoms near the O-vacancy are substituted by the Mo or Fe atoms.

Effect of Titanium Doping of Lithium-Rich Cathode Materials

Effect of Titanium Doping of Lithium-Rich Cathode Materials

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.

Boosting Electrochemical Performance of Lithium-Rich Manganese-Based Cathode Materials through a Dual Modification Strategy with Defect Designing and Interface Engineering

Low Coulombic efficiency, severe capacity fading and voltage attenuation, and poor rate performance are currently great obstacles for the industrial application of lithium-rich manganese-based cathode materials (LRMCs) in lithium-ion batteries (LIBs). Herein, a dual modification strategy combining defect designing with interface engineering is reported to solve the above problems synchronously. Oxygen vacancies, a carbon nitride protective layer, and a fast ion conductor are simultaneously introduced in the LRMCs. It has been found that oxygen vacancies can suppress the release of irreversible oxygen, which is in favor of improving the initial Coulombic efficiency, the carbon nitride protective layer can improve the structural stability and alleviate the attenuation of capacity and voltage, and the fast ion conductor can promote the diffusion rate of Li+ and electron conductivity and thus enhance the rate capability. The modified material exhibits significantly enhanced electrochemical performances, including a favorable capacity retention rate of 94.2% over 120 cycles at 1C (1C = 200 mAh g-1) and excellent rate capabilities of 173.1 and 136.9 mAh g-1 can be maintained at 5 and 10C after 100 cycles, respectively. Hence, the well-designed dual modification strategy with defect design and interface engineering provides significant exploration for the development and industrialization of LRMCs with high performance.