Lithium-rich Cathode Research Articles

Towards High-Performance Li-Rich Cathode Materials: from Morphology Design to Electronic Structure Modulation.

Lithium-rich cathode materials (LRMs) have garnered significant interest owing to their high reversible discharge capacity (exceeding 250 mAh g⁻¹), which is attributed to the redox reactions of transition metal (TM) ions as well as the distinctive redox processes of oxygen anions. However, there are still many problems, such as their relatively poor rate performance and voltage fading and hysteresis, hindering their practical applications. Herein, the recent insights into the mechanisms and the latest advancements in the research of LRMs are discussed. Strategies to promote the performance of LRMs are discussed following a top-down approach from the morphology design to electronic structure modulation. Finally, the ongoing efforts in this area are also discussed to inspire more new ideas for the future development of LRMs.

Regulating the Intralayer Cation Disorder in Layered Lithium-Rich Cathodes to Improve Cycle Performance.

The Li/Mn ordered structure of lithium-rich (LR) cathodes leads to the heterogeneous Li2MnO3 and LiTMO2 components, readily triggering structural degeneration and performance degradation in long-term cycling. However, the lack of guiding principles for promoting cation disorder within the transition metal (TM) layers has posed a persistent challenge in designing homogeneous layered LR cathodes. Herein, the (Li + Mn)TM content in the TM layer as a criterion for the design of cation-disordered layered LR cathodes is proposed. The intralayer cation disorder can be achieved by tuning the (Li + Mn)TM content less than 0.5 combined with incorporating the solute ions with suitable ionic radii. For a multicomponent LR nickel cobalt manganese (LRNCM) oxides system, multiscale structural analyses reveal that cation-disordered layered Li1.1(Ni0.6Co0.1Mn0.3)0.9O2 (LR613) exhibits enhanced compositional homogeneity and higher R m symmetry. The developed LR613 cathode undergoes a solid-solution reaction during Li+ deintercalation and mitigates voltage decay during cycling. It is elucidated that intralayer cation disorder effectively alleviates microstrain within the cathode structure and enhances overall structural stability. This comprehensive understanding of the composition-structure-electrochemical behavior relationship inspires the development of durable cation-disordered layered LR cathodes through composition tuning.

Inorganic-Dominated Interphase Enabled by Tuning Solvation Configuration for 4.8 V Lithium-Ion Batteries.

Constructing a dense inorganic component-dominated cathode electrolyte interphase (CEI) to meet the long-term cycling requirements of ultrahigh voltage cathodes has been a crucial challenge. Nevertheless, this goal is difficult to achieve in traditional electrolyte compositions due to the inevitable decomposition of organic solvents. Herein, by utilizing the localized mismatch between the strongly coordinating hexafluorophosphate anion (PF6-) and the weakly coordinating solvent 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide (TFDMSA), abundant aggregates (AGGs) emerged under a regular Li salt concentration of 1 m lithium bis(fluorosulfonyl)imide (LiFSI) + 0.1 m LiPF6 in TFDMSA. This anion-rich Li+ solvation structure results in an inorganic-dominated LiF-rich CEI to suppress phase transitions of lithium-rich manganese-based cathode materials (LLMO). Consequently, the prepared LLMO||Li half-cells demonstrate a capacity retention of 80.7% after 350 cycles at 4.8 V. This work advances the practical application of new electrolyte systems by proposing a new approach to construct anion-dominated Li+ solvation structures in local environments.

Enhanced performance of lithium-ion battery cathodes using a composite conductive network of CNTs, GQDs, and GNRs embedded in Li₁.₂Mn₀.₅₄Ni₀.₁₃Co₀.₁₃O₂ (LMNCO)

Lithium-rich Li-ion battery cathode materials are known for their high specific capacities and working potential. However, their practical application is limited by the significant decline in discharge potential and capacity during repeated cycling. In this study, we introduce a highly conductive electrode architecture, encapsulating within carbon nanotubes (CNTs), graphene nano-ribbons (GNRs) and graphene quantum dots (GQDs) to mitigate rapid capacity fading and suppress voltage decay. Three Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials were synthesized. The first sample, pristine Li-rich L1.2Mn0.54Ni0.13Co0.13O2, was synthesized using a nitrate co-precipitation method. The second cathode, GNRs-CNTs@Li1.2Mn0.54Ni0.13Co0.13O2, incorporates a mixture of carbon nanotubes and graphene nanoribbons. The third cathode, GQDs:GNRs-CNTs@Li1.2Mn0.54Ni0.13Co0.13O2), further integrates graphene quantum dots within the graphene nanoribbons and carbon nanotubes matrix. The inclusion of highly conductive GNRs-CNTs and GQDs effectively enhances the electrical conductivity of L1.2Mn0.54Ni0.13Co0.13O2, increasing the specific capacity from 246.95 to 316.94 mAhg−1. Additionally, GQDs prevent side reactions and surface phase transitions, thereby improving thermal stability.

Co-free gradient lithium-rich cathode for high-energy batteries with optimized cyclability

Lithium-rich layered oxides (LLOs) hold the promise for high-energy battery cathodes. However, its application has been hindered by voltage decay associated with irreversible reactions at high voltages despite decades of intensive efforts. Here, we first theoretically studied the molecular orbitals of Mn-based Li-rich configurations. We found that the π-bond ring formed within the LiMn6 structure could participate in stable redox reactions as one unit, but Co could disrupt its symmetry. We thus designed and synthesized Co-free concentration-gradient LLOs (CF-CG-LLOs) materials. The combination of concentration gradient and Co removal leads to exceptional capacity retention without any fading over 100 cycles of the pouch cell. More importantly, it exhibits an extraordinarily low voltage decay of 0.15 mV/cycle, accompanied by a high Coulombic efficiency of 99.86%. This concept and demonstration of CF-CG-LLO cathodes reveal a viable avenue toward low-cost, high-energy-density battery cathodes.

Degradation, Intrinsic Microstrains, and Phase Structure Engineering in Lithium-Rich Oxide Cathode Materials

Degradation, Intrinsic Microstrains, and Phase Structure Engineering in Lithium-Rich Oxide Cathode Materials

The mechanism of the impact of Li2MnO3 with dual-edged sword functionality on the cyclic performance of lithium-rich manganese-based cathode materials

The Li2MnO3 phase is a double-edged sword hanging over lithium-rich manganese-based cathode materials (LLOs). It provides a theoretical specific capacity of over 300mAh/g for LLOs, but it is also the main source of issues such as low Initial Coulombic efficiency (ICE), poor rate performance, and voltage decay. In recent years, related research has primarily focused on the lattice oxygen. From the perspective related to the Li2MnO3 phase, this study achieves different activation degrees of Li2MnO3 phase through ingenious electrochemical methods. It conducts a detailed analysis of the phase transition and polarization of Li2MnO3 phase under high and low rates, and delves into the different mechanisms that cause the electrochemical performance degradation of LLOs under high and low rates. The results show that during low-rate cycling, the more Li2MnO3 phase in LLOs, the more transformation of crystal structure from layered to spinel phase occurs during cycling, and the structural transformation of the material will ultimately lead to the degradation of cycle performance and voltage decay. During high-rate cycling, due to the intrinsic conductivity difference of Li2MnO3 phase, the large polarization effect of LLOs can lead to severe decomposition of the electrolyte at high voltages, resulting in the degradation of cycle performance. Therefore, conducting research on LLOs focused on the Li2MnO3 phase may be an effective approach, providing a new modification idea for achieving more excellent cycling performance of LLOs.

Entropic Design of Anionic Site to Improve Anionic Redox Stability in Lithium-Rich Cathode.

Cobalt-free manganese-rich layered oxide is considered one of the most promising cathode materials for next-generation lithium-ion batteries due to its high capacity and low cost. However, irreversible anionic redox (OAR) leads to serious failure problems and hinders its wide application. To solve the above problems, the entropy design strategy of anionic sites is proposed, which is more direct and relevant to the regulation of the OAR process compared to the traditional entropy design of TM sites. The entropic design improves the structural diversity and long-range disorder of the material, which effectively inhibits oxygen release and drastic structural strain, and alleviates structural degradation. After 400 cycles at 1C, the capacity and voltage decay per cycle are only 0.092 mAhg-1 and 1.36mV, respectively. The long cycle test (10C and 1000 cycles) at high current shows that the voltage and capacity decay are only 0.04 mAhg-1 and 0.66mV per cycle, respectively. Meanwhile, the rate performance at 10C reaches 175 mAhg-1. The charge compensation regulation and performance enhancement mechanism are investigated by systematic in-situ/ex-situ characterization and theoretical calculation. This research provides new ideas for the design of lithium-rich cathodes with stable OAR and high structural adaptability.

Study of Pr doped nanocrystalline LiCoO2 cathode material for spintronic and energy storage applications: A theoretical and experimental analysis

In this study, Pr3+ substituted LiCoO2 lithium-rich cathode materials were prepared using the sol-gel auto-combustion technique to enhance cycling performance. LiCo1-xPrxO2 samples having Pr concentrations x = 0.00–0.10 were synthesized. X-ray diffraction (XRD) showed a rhombohedral structure with space group R-3m, further verified by the Rietveld refinement. Field emission scanning electron microscopy (FESEM) revealed the presence of distinct and well-defined submicron-scale grains. FTIR spectroscopy confirmed Co–O stretching bonds within 590–560 cm−1 and revealed peaks at around 560–590, 830–860, and 1320-1480 cm−1, which could be attributed to the electrochemical performance of Pr-doped species. Moreover, EDX spectroscopy confirmed the typical elemental peaks of only Co, Pr, and O, confirming the required phase presence. The cyclic voltammetry showed improved reversibility and stability due to Pr doping. The first-principles computations were performed using the lattice constant extracted from XRD measurements. The pure LiCoO2 with a semiconducting nature became half-metallic due to Pr doping (LiCo0.84Pr0.16O2). The magnetic properties indicate that LiCoO2 and LiCo0.84Pr0.16O2 exhibit positive magnetic order, which shows that these are suitable candidates for spintronic applications. The pure LiCoO2 revealed intercalation voltages of 4.10–2.73V and a theoretical capacity 40–203 mAh/g. Meanwhile, for LiCo0.84Pr0.16O2, the intercalation voltages and theoretical capacity improved to 4.42–2.85 V and 42 to 211 mAh/g, respectively. The combined experimental and theoretical study suggests that Pr-doped LiCoO2 is suitable for spintronic applications and energy applications such as composite cathodes.

Improving the electrochemical performance of lithium-rich manganese-based cathode materials by Na₂S₂O₈ surface treatment

Lithium-rich manganese-based cathode materials are well-regarded for their high specific capacity and notable voltage thresholds, making them attractive for advanced energy storage applications. However, their widespread commercialization is hindered by challenges in cycle performance, including suboptimal initial Coulombic efficiency, inadequate cycle stability, and constrained rate capability. To address these issues, this paper introduces a novel modification strategy using Na₂S₂O₈ to chemically delithiate the surface of the materials. This modification strategy dramatically enhances the initial Coulombic efficiency. The results demonstrate that the initial Coulombic efficiency of the two pre-activated samples improved to 84.6 % and 102.2 %, respectively. At the same time, the Na₂S₂O₈-treated samples exhibit a higher maximum discharge capacity at a 0.2 C rate, reaching 211.1 mAh g⁻¹ and 201.3 mAh g⁻¹, which notably surpasses the untreated sample's capacity of 188.7 mAh g⁻¹. Additionally, the treated samples exhibit improved cycling and rate performance, with capacity retention of 81.2 % and 63.5 %, respectively. After 60 cycles, these figures continue to be superior to those of the untreated material, which stands at 57.3 %. The results demonstrate that Na₂S₂O₈ treatment leads to the in situ formation of spinel phases on the material surface, thereby enhances the cycling stability and rate capability of the cathode material. Compared to traditional surface treatment methods, Na₂S₂O₈ solution treatment can induce more profound structural evolution without necessitating high-temperature calcination, thus reducing the demands on process conditions and equipment and offering greater process controllability. Moreover, this surface modification strategy paves the way for applying spinel coatings on other substrates with similar structures.

Effect of Rare Earth Ion Doping on the Performance of Lithium-Rich Cathode Materials for Lithium-Ion Batteries

Lithium-rich layered oxide cathode materials have the advantages of a high voltage and a high specific capacity. Their commercial applications have however been impeded by some disadvantages such as low initial coulombic efficiency and low cycle life. To overcome these issues, rare earth ion-doped lithium-rich layered oxide cathode materials are investigated in this work. The irreversible release of O2- in Li2MnO3 is suppressed by rare earth ions doping, which enhanced the initial coulombic efficiency of the materials. Meanwhile, the rare-earth ion radius used for doping is larger than the Mn4+ radius, which enlarges the (003)-crystalline plane spacing, resulting in a significant enhancement of the rate performance of the material.

Performance improvement strategies of boron-doped lithium-rich layered oxide cathode materials for wide temperature condition

Herein, the boron-doped Li-rich materials are prepared by rapid nucleation-assisted solvothermal and high-temperature method. In this work, the effects of boron doping on crystal structure and cycling performances of as-prepared materials were investigated. The material characterization results show that the introduction of B reduces the TM valence, enlarges the (003) space distance, and modulates the local crystal structure, which may change the electrochemical performance of as-prepared samples. Li1.2Ni0.24Co0.08Mn0.48B0.02O2 (LLNCMBO-2) showed an increase in discharge capacity of 36.5 mAh g−1 at 0.1 C compared to the pristine sample. The LLNCMBO-2 exhibit high capacity retention of 85.50 % after 200 cycles with a voltage decay of only 254.9 mV. Additionally, the results of wide temperature testing show that the electrochemical performance of boron-doped samples improved evidently.

Precisely designed 3-stage calcination strategy for lithium-rich manganese-based cathodes with improved cycling performance

The poor cycling performance of Li-rich manganese-based (LMR) cathodes is one of the challenges that need to be urgently overcome. Enhancing the stability of the layered structure responsible for lithium-ion diffusion is an effective way to improve the cycling performance. Layered structures are mainly formed during the high-temperature solid-phase reaction, whereas the prolonged and constant-high-temperature calcination conditions in conventional calcination procedure may pose a threat to the layered structural stability. Thus, in order to optimize the formation environment of layered structures under high-temperature solid-phase reaction, we have designed suitable temperature-controlled strategies for each stage of layered structure formation, gradual maturation, and post-treatment, respectively, referred to as the 3-stage calcination strategy. This calcination strategy contributes to the formation of a more ordered and stable layered structure, which significantly improves the cycling performance of LMR cathodes (capacity retention rate of 85.2 % after 200 cycles at 1C). The shortening of the constant high temperature calcination time helps to further reduce the production cost of the batteries. The design concept of this work is to regulate the formation process of layered structures in stages, which provides inspiration for the efficient and controllable synthesis of electrode materials with excellent structural stability at low production cost.

Lithium-rich manganese-based layered oxide cathode materials for lithium-ion batteries modified by MoS2 coatings with two-dimensional graphene-like structures

Lithium-rich manganese-based layered oxide cathode materials (LRMCs) have some unique advantages such as high theoretical capacity (≥ 250 mAh g−1) and high energy density. Therefore, they are deemed as a kind of cathode material for lithium-ion batteries with an excellent prospect of application. However, the redox of oxygen anion is able to generate irreversible lattice oxygen loss, leading to irreversible loss of capacity, bringing about a sharp drop of working voltage, and seriously restricting the commercialization of LRMCs. In this paper, MoS2 coating with two-dimensional graphene-like structure was coated on the surface of LRMCs materials for improving the cycling stability and rate performance. The MoS2 coating can provide a two-dimensional diffusion channel for the migration of lithium-ions, which facilitates the fast release of lithium-ions during cycling process. The results show that the first discharge capacity, initial Coulomb efficiency and rate performance of LRMCs are improved. When the current density is 1 C, the first discharge specific capacity of LRMCs@MoS2 reaches 227.69 mAh g−1, and the capacity retention ratio is 84.98 % after 100 cycles. When the current density is 5 C, it can still provide a discharge specific capacity of 137.87 mAh g−1, demonstrating excellent electrochemical performance. This study comes up a simple and practical idea to realize the modification of cathode materials for high performance lithium-ion batteries.

Surface Reconstruction Enhanced Li-Rich Cathode Materials for Durable Lithium-Ion Batteries.

Regulating the distribution of surface elements in lithium-rich cathode materials can effectively change the electrochemical performance of cathode materials. Considering that the enrichment of Mn element on the surface is the main reason for the irreversible phase transition and dissolution of its surface structure, which in turn is the main reason for performance degradation. Based on the molten salt-assisted sintering method, a lithium rich cathode material with surface rich Ni and Co is designed and prepared. The surface enrichment of Ni and Co effectively reduces the dissolution of Mn, promotes the occurrence of irreversible collapse of surface structure from layered phase to rock salt phase on the material surface, improves the stability of surface crystal phase structure, and improves the cycling stability of positive electrode materials. Notably, after 500 cycles at 1 C current density, the discharge-specific capacity attained 189.8 mAh g -1, with a capacity retention rate of 88.9%, indicating a 42.1% improvement in capacity retention. Molten salt treatment is widely used in the modification of positive electrode materials. The research work will provide new ideas for improving the stability of lithium rich materials and promoting their commercial applications.

Effect of sites of doped Mg on the stability of lattice oxygen in lithium-rich manganese-based cathode materials

Elemental doping is considered as an effective method for altering the localized electronic structure of lattice oxygen in lithium-rich manganese-based oxides (LRMO) and enhancing their structural stability. However, the effect of doping heteroatoms at different sites on the oxygen redox is not clear. In this work, Mg is introduced into transition metals (TM) and lithium (Li) sites of LRMO at co-precipitation stage and lithiation stage to prepare LRMO-TM and LRMO-Li, respectively. The experimental results and density-functional theory calculations demonstrate that the oxygen release is reduced from 4.1653 nmol mg−1 of pristine to 3.3886 nmol mg−1 of LRMO-Li, and 2.7688 nmol mg−1 of LRMO-TM. The reduction of oxygen release of LRMO-Li is related to the formation of strong Mg-O interactions. Different from that, the lower oxygen release of LRMO-TM is mainly due to the reduction of electron holes in the O 2p state caused by the weaker Mn-O covalency, which effectively restricts the over-oxidization of oxygen. The capacity retention of LRMO-TM is 85.18 % at 0.2C after 200 cycles, which is higher than that of LRMO (78.63 %) and LRMO-Li (82.28 %). This work reveals the mechanism of enhancing lattice oxygen stability caused by Mg doping at different sites.

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.

Achieving the dual regulation of microstructure and microdefects in lithium rich materials by electrospinning technology

Lithium-rich manganese-based cathode materials (LNCM) have garnered tremendous attention for the superior reversible capacity. However, the inherently unstable structure and low diffusion kinetics of Li+ hamper their commercialization process. Recent studies have shown that void defects within grains are the main cause of oxygen release and voltage drop during cycling. Therefore, highly crystallinity small particles are the ideal structure for high power density and cycling stability of LNCM. However, improving the crystallinity of materials often means increasing the sintering temperature, which can easily cause material aggregation and grain growth. In this paper, by adopting the electrostatic spinning technology, nanowire shaped precursor are constructed, which facilitates the direct contact between the hot gas flow and the precursor during sintering, thus promoting ion diffusion and material crystallinity. Besides, the electronic and chemical environment in the modified LNCM sample have regulated simultaneously, accompanying with a significant increase in O vacancies, Mn4+ and Ni3+ ions. Adjustments from morphology to molecular structure increased the contact area between the material and electrolyte, improved the diffusion ability of Li+, and enhanced structural stability of the material, resulting in improved rate performance and cycling stability. This study expands our understanding of adopting electrospinning technology to prepare high-performance materials.

Lithium salt preprocessing calcination strategy for a more stable layered structure of lithium-rich manganese-based cathodes

The poor cycling performance of lithium-rich manganese-based (LMR) cathodes limits their practical applications. The stability of the layered structure is closely related to the cycling performance. The high-temperature solid-state reaction between transition metal oxides (TMOs) and lithium salts promotes the formation of the layered structure, which determines the quality of the layered structure. Considering the influence of physicochemical changes of the lithium salt on the formed layered structural stability, in this work, the calcination strategy includes a short period of holding time near the melting point of Li2CO3, referred to as the lithium salt preprocessing calcination strategy, which allows the molten Li2CO3 to be fully contacted with TMOs at relatively low temperatures, alleviating the problem of Li in the thermal decomposition products of Li2CO3 not easily further reacting with TMOs. Compared to the conventional calcination procedure, this new calcination strategy reduces the oxygen vacancy concentration as well as the relative Mn3+ content on the surface of the cathodes, which significantly improves the cycling performance. In addition, the shortening of the constant high temperature calcination time effectively reduces the production energy consumption, which provides a reference for the future efficient and low-cost synthesis of electrode materials with excellent cycling performance.

Comprehensive Review of Li-Rich Mn-Based Layered Oxide Cathode Materials for Lithium-Ion Batteries: Theories, Challenges, Strategies and Perspectives.

Lithium-rich manganese-based layered oxide cathode materials (LLOs) have always been considered as the most promising cathode materials for achieving high energy density lithium-ion batteries (LIBs). However, in practical applications, LLOs often face some key problems, such as low initial coulombic efficiency, capacity/voltage decay, poor rate performance and poor cycle stability. It seriously shortens the lifespan of lithium-ion batteries and hinder the large-scale commercial application of LLOs. Herein, firstly, the basic theories of LLOs were systematically reviewed, including the structural characteristics, the working mechanism of LLOs, the preparation methods of LLOs (liquid phase co-precipitate method, sol-gel method, hydrothermal synthesis method, solid phase method, low heat solid-phase method, high temperature solid-state method etc.), and electrochemical characteristics of LLOs (first charge discharge characteristics and reversible efficiency, cycling performance, high and low temperature performance and thermal stability etc.). Then, key challenges faced by LLOs were systematically discussed. Finally, the LLOs modification strategies used to address these challenges (element doping, surface modification, defect engineering, structural and morphological control etc.) were elaborated in detail. This important review provides potential insights and directions for further improving the electrochemical performance of LLOs, and provides a necessary theoretical basis for accelerating the large-scale commercial application of LLOs. It possesses important scientific research value and far-reaching social significance.