Lithium-rich Cathode Research Articles

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

Sulfur-Assisted Surface Modification of Lithium-Rich Manganese-Based Oxide toward High Anionic Redox Reversibility.

Energy storage via anionic redox provides extra capacity for lithium-rich manganese-based oxide cathodes at high voltage but causes gradual structural collapse and irreversible capacity loss with generation of On - (0 ≤ n < 2) species upon deep oxidation. Herein, the stability and reversibility of anionic redox reactions are enhanced by a simple sulfur-assisted surface modification method, which not only modulates the material's energy band allowing feasible electron release from both bonding and antibonding bands, but also traps the escaping On - via an as-constructed SnS2- x - σ Oy coating layer and return them to the host lattice upon discharge. The regulation of anionic redox inhibits the irreversible structural transformation and parasitic reactions, maintaining the specific capacity retention of as-modified cathode up to 94% after 200 cycles at 100mA g-1 , along with outstanding voltage stability. The reported strategy incorporating energy band modulation and oxygen trapping is promising for the design and advancement of other cathodes storing energy through anion redox.

Easy and Scalable Syntheses of Li1.2Ni0.2Mn0.6O2

Solid-state and sol-gel syntheses were selected as easy and scalable methods to prepare a lithium-rich cathode material for lithium-ion batteries. Among the extended family of layered oxides, Li1.2Ni0.2Mn0.6O2 was chosen for its low nickel content and the absence of cobalt. Both synthesis methods involved two heating steps at different temperatures, 600 and 900 °C. The first step is needed to decompose the metal acetates, which were selected as precursors, and the second step is needed to crystallise the material. To obtain a material with well-defined defects, the rate of heating and cooling was carefully controlled. The materials were characterised by X-ray diffraction, SEM coupled with EDS analysis, and thermal analysis and were finally tested as cathodes in a lithium semi cell. The solid-state synthesis allowed us to obtain better structural characteristics with respect to the sol-gel one in terms of a well-formed hexagonal layer structure and a reduced Li+/Ni2+ disorder. On the other hand, the sol-gel method produced a material with a higher specific capacity. The performance of this latter material was then evaluated as a function of the discharge current, highlighting its good rate capabilities.

Using molten-salts as a thermal processing medium for cobalt-free lithium-rich cathode material

Lithium-rich nickel manganese oxide cathode materials are well known to have limited rate capabilities. In this investigation we demonstrate that modifying a common sol-gel synthetic route by adding simple salts to the precursors during firing can create a molten-salt environment for the synthesis of the material that may results in improved materials and performance attributes. After screening multiple salt species, our findings indicate that the use of NaCl can provide a cost-effective and facile method for increasing the rate capability of these materials.

Realizing primary/secondary particle co-coating with CoxB for lithium-rich cathodes in high-performance lithium-ion batteries

The construction of a surface protection layer is an important way to improve the cycling stability of lithium-rich manganese-based cathode materials. However, the protection for the primary particles inside is usually neglected compared with the secondary particles, which increases the corrosion risk of the electrolytes. In view of this, amorphous CoxB coated Li1.2Mn0.54Ni0.13Co0.13O2 (LMNCO) was rationally designed and prepared. Nano CoxB not only completely coated the surface of the secondary particles but also penetrated between the grain boundaries of the primary particles to achieve the protection of the primary particles. Thus, the cycling stability of the LMNCO is improved significantly. After 200 cycles at 1C and 25°C, the capacity loss rate of CoxB-LMNCO is 8.9%. Even at 2C and 40°C, the value is only 13.4%. As a result, this work provides a new idea to improve the electrochemical performances of the LMNCO cathode materials in high-performance lithium-ion batteries.

Limiting cobalt fraction in lithium rich cathode materials for stable and fast activation

Li-rich layered oxides (LRLOs) have been considered as promising cathode materials for high-energy Li-ion batteries. However, considerable fractionsof costly Co and Ni are normally needed in LRLOs to access the high capacity. In this work, a series of Ni/Co-poor LRLOs is designed to study the effect of Ni:Co ratio on their electrochemical behavior. Due to the lowest-lying Co t2g band, the introduction of minor Co significantly promotes the activation of Li-rich phase. While high Co content exacerbates the interfacial reactions to form a thick and unstable cathode-electrolyte film. Consequently, the low-Co LRLO (ca. 4 % of transition metal) attains stable and fast activation, maintaining 233.3 mA h g−1 after 300 cycles at 1C. Moreover, the low-Co LRLO//graphite full cell retains 86.4 % of its capacity after 200 cycles. This work will shed light on the compositional design of LRLOs towards higher electrochemical performance and lower materials cost.

Rapid preparation of cobalt-free lithium rich cathode materials with layered structure and excellent performance via capillary microreactors

High voltage and high energy density cathode materials are the future development trend of power batteries. Li-and Mn-rich layered oxide (LMR) materials exhibit high capacity, low cost, and environmental friendliness, making them a promising cathode material for the next generation of lithium-ion batteries. In this study, a continuous-flow process for rapid co-precipitation synthesis of LMR precursor (Mn0.75Ni0.25CO3) in capillary microreactors was developed. Due to the good mixing characteristics of the microreactor (tm=54 ms), Mn0.75Ni0.25CO3 displays a complete spherical morphology and uniform elemental distribution without adding any complexing agent during the synthesis. The reaction time can be controlled within 11.78 s. The prepared Li1.2Mn0.6Ni0.2O2 (LMR) cathode exhibits excellent properties with a high initial discharge capacity of 266.52 mAh•g−1 at 0.1C and a superior capacity retention of 93.7 % after 200 cycles at 1C. This work demonstrates that microfluidic technology presents a viable and promising approach for quickly producing lithium battery cathode precursors.

Aluminum-doping induced micro-porous structure and improved anion redox reversibility in cobalt-free lithium-rich cathode materials for its enhanced electrochemical performance

Aluminum-doping induced micro-porous structure and improved anion redox reversibility in cobalt-free lithium-rich cathode materials for its enhanced electrochemical performance

4d Lithium-Rich Cathode System Reinvestigated with Electron Paramagnetic Resonance: Correlation between Ionicity, Oxygen Dimers, and Molecular O2.

Layered lithium-rich (Li-rich) oxide cathodes with additional capacity contribution via oxygen redox are promising high energy density cathodes for next generation Li-ion batteries. However, the chemical states of the oxidized oxygen in charged materials are under fierce debate, including the O2- with stable electron holes, O-O dimer (O2)n- (n > 0), molecular O2, and oxygen π redox. Here, we show using electron paramagnetic resonance (EPR) spectroscopy that in the 4d Li-rich ruthenate compounds, Li2Ru0.75Sn0.25O3 and Li2Ru0.5Sn0.5O3, strong covalency between 4d transition metal and oxygen can inhibit the formation of trapped molecular O2 but not suppress the formation of O-O dimer. As the covalent bond of Ru-O weakens and the ionic bond Sn-O becomes dominant in Li2Ru0.25Sn0.75O3, (O2)- will detach from Sn4+, eventually leading to the formation of trapped molecular O2 during the deep oxygen redox. We propose two possible evolution paths of oxidized oxygen as (1) oxygen electron holes → Ru-(O2)m- (m > 1) → Ru-(O2)- or (2) oxygen electron holes → Sn-(O2)m- (m > 1) → Sn-(O2)- → O2, and the species to which they will evolve are related to which metal (O2)- bonds to and whether the ionicity dominates.

Cathode Electrolyte Interface Engineering by Gradient Fluorination for High‐Performance Lithium Rich Cathode

AbstractDespite their ultrahigh specific capacity, lithium‐rich layered oxide cathodes are still plagued by challenges such as poor cycle stability and notorious voltage decay, which are primarily attributed to surface issues such as the release of lattice oxygen and interfacial side reactions. In this study, a facial strategy of gradient fluorination is adopted to construct a thin but robust LiF‐rich cathode electrolyte interface (CEI), highly enhancing the stability of the interface of lithium‐rich oxides. Experimental results and theoretical calculations both demonstrate that the stable CEI not only promotes oxygen participation in redox reactions and simultaneously inhibits oxygen release and structural transition, but also facilitates the transport kinetics of lithium ions. As a result, the gradient fluorinated lithium‐rich cathode delivers highly enhanced rate performance (133 mAh g−1 at 5 C), superior cycling stability with a capacity retention of 81.9% after 100 cycles at 1 C (250 mAh g−1), and alleviated voltage fade (only 1.75 mV per cycle). Moreover, a unique formation mechanism for LiF‐rich surfaces is proposed according to theoretical calculations. This work not only provides a fresh understanding of the CEI formation mechanism, but also show a promising avenue for designing LiF‐rich CEIs applicable to other layered oxide cathodes.

Lithium-Ion Conductor Li2ZrO3-Coated Primary Particles To Optimize the Performance of Li-Rich Mn-Based Cathode Materials.

A lithium-rich manganese-based cathode material (LRMC) is currently considered as one of the most promising next-generation materials for lithium-ion batteries, which has received much attention, but the LRMC still faces some key scientific issues to break through, such as poor rate capacity, rapid voltage, capacity decay, and low first coulomb efficiency. In this work, homogeneous Li2ZrO3 (LZO) was successfully coated on the surface of Li1.2Mn0.54Ni0.13Co0.13O2 (LRO) by molten salt-assisted sintering technology. Li2ZrO3 has good chemical and electrochemical stability, which can effectively inhibit the side reaction between electrode materials and electrolytes and reduce the dissolution of transition metal ions. Thus, the as-prepared LRO@LZO composites are expected to improve the cycling performance. It can be found that the discharge specific capacity of LRO is 271 mAh g-1 at 0.1 C, and the capacity retention rate is still 93.7% after 100 cycles at 1 C. In addition, Li2ZrO3 is an excellent lithium-ion conductor, which is prone to increasing the lithium-ion transfer rate and improving the rate capacity of LRO. Therefore, this study provides a new solution to improve the structure stability and electrochemical performance of LRMCs.

Slab gliding, a hidden factor that induces irreversibility and redox asymmetry of lithium-rich layered oxide cathodes

Lithium-rich layered oxides, despite their potential as high-energy-density cathode materials, are impeded by electrochemical performance deterioration upon anionic redox. Although this deterioration is believed to primarily result from structural disordering, our understanding of how it is triggered and/or occurs remains incomplete. Herein, we propose a theoretical picture that clarifies the irreversible transformation and redox asymmetry of lithium-rich layered oxides by introducing a series of global and local dynamic structural evolution processes involving slab gliding and transition-metal migration. We show that slab gliding plays a key role in trigger/initiating the structural disordering and consequent degradation of the anionic redox reaction. We further reveal that the ‘concerted disordering mechanism’ of slab gliding and transition-metal migration produces spontaneously irreversible/asymmetric lithiation and de-lithiation pathways, causing irreversible structural deterioration and the asymmetry of the anionic redox reaction. Our findings suggest slab gliding as a crucial, yet underexplored, method for achieving a reversible anionic redox reaction.

Durable lithium-ion insertion/extraction and migration behavior of LiF-encapsulated cobalt-free lithium-rich manganese-based layered oxide cathode

Lithium-rich manganese-based cathode has made a subject of intense scrutiny for scientists and application researchers due to their exceptional thermal stability, high specific capacity, high operating voltage, and cost-effectiveness. However, the inclusion of cobalt, as a crucial component in lithium-rich manganese-based cathode materials, has become a cause for concern due to its limited availability and non-renewable nature, which eventually limits the growth of the battery industry and increase costs. Considering the poor stability of cobalt-free cathode, this work proposes a coating strategy of LiF through a simple high-temperature melting method. Directly coating LiF on Li1.2Ni0.2Mn0.6O2 surface is found to be an effective way to protect the cathode material, decrease metal solubility, and inhibit irreversible phase transition processes, thus leading to an improved electrochemical performance. As a result, the battery employing LiF coated Li1.2Ni0.2Mn0.6O2 cathode can be stabilized over 280 cycles and maintain a capacity of 110 mAh g−1 at 1C. What’s more, the mechanisms of ion insertion/extraction behavior and ion migration process are also studied systematically. This study will open the avenue to develop a high-energy battery system with cobalt-free cathode.

High-Capacity Oxide Cathode beyond 300 mAh/g

The pursuit of high-energy-density lithium-ion batteries (LIBs) hinges upon the relentless development of advanced cathode materials. The inherent high operating voltage renders oxide cathodes the most favored option for this objective. Even with the exceptional capacity of ∼300 mAh/g exhibited by lithium-rich manganese oxide cathodes, the cell-level energy density at present remains constrained at 400 Wh/kg. Consequently, a transformative breakthrough is urgently needed to revolutionize oxide cathode materials with ultrahigh capacity (>300 mAh/g) and thereby enable the design of LIBs for a broad range of applications. In this Focus Review, the electrochemical performances of various oxide cathodes are comprehensively scrutinized, with particular emphasis on those characterized by a Li/O ratio greater than 0.6 (Li1+xTM1–xO2, x > 0.2, where TM denotes transition metal). We emphasize that the construction of multidimensional defects offers a promising means of resolving the present quandary regarding the trade-off between structural stability and capacity for high-capacity oxide cathodes.

Enhancing Ionic Transport and Structural Stability of Lithium-Rich Layered Oxide Cathodes via Local Structure Regulation.

Lithium-rich manganese-based layered oxides (LRM) have garnered considerable attention as cathode materials due to their superior performance. However, the inherent structural degradation and obstruction of ion transport during cycling lead to capacity and voltage decay, impeding their practical applications. Herein, an Sb-doped LRM material with local spinel phase is reported, which has good compatibility with the layered structure and provides 3D Li+ diffusion channels to accelerate Li+ transport. Additionally, the strong Sb-O bond enhances the stability of the layered structure. Differential electrochemical mass spectrometry indicates that highly electronegative Sb doping effectively suppresses the release of oxygen in the crystal structure and mitigates successive electrolyte decomposition, thereby reducing structural degradation of the material. As a result of this dual-functional design, the 0.5 Sb-doped material with local spinel phases exhibits favorable cycling stability, retaining 81.7% capacity after 300 cycles at 1C, and an average discharge voltage of 1.87mV per cycle, which is far superior to untreated material with retention values of 28.8% and 3.43mV, respectively. This study systematically introduces Sb doping and regulates local spinel phases to facilitate ion transport and alleviate structural degradation of LRM, thereby suppressing capacity and voltage fading, and improving the electrochemical performance of 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.

Nano-micron composite lithium-rich cathode materials prepared by oxalic acid one-step method

Lithium-rich material (SOP) with special nano-micron composite structure is synthesized by simple one-step oxalic acid method. The SOP sample is made of micron particles (1–3 μm) and nano-particles (~ 100 nm). Compared with the co-precipitation prepared lithium-rich materials (COP), SOP has good rate performance and cycle stability. The specific discharge capacity of SOP sample reaches 104.2 mAh/g at 10 C, while that of COP sample is only 68.5 mAh/g. After 300 cycles, SOP still has a specific discharge capacity of 201 mAh/g and the capacity retention rate is 89.6%, while COP only has a specific discharge capacity of 135.8 mAh/g and the capacity retention rate is 58%. Structure allocation with nano-micron particles is conducive to electrochemical performance improvement. This study provides a new idea for the synthesis of lithium-rich material with better performance.

Quadruple modification for constructing ultra-stable lithium-rich cathodes

Lithium-rich layered oxides are considered as the next generation cathode materials for lithium-ion batteries due to their high capacity and operating voltage. However, O2 release, side reactions at the cathode-electrolyte interface, transition metal(TM) dissolution, and microcracking evolution severely limit the commercial application of Li-rich cathode materials. In this work, the Eu is used to modify the Li1.2Mn0.54Co0.13Ni0.13O2 for the lithium-rich cathode. The doping of Eu in the bulk phase greatly improves the redox activity of the material, and a large number of oxygen vacancies extremely alleviate the irreversible changes of lattice oxygen. The Eu2O3 modified layer at the interface and the heterogeneous structure of the rock-salt phase effectively ensure the structural integrity and stability of the CEI during long time cycling, disturbing the orientation of the non-bonded O 2p orbitals. The attenuation of specific capacity (0.04 mA h g−1/cycle) and voltage (0.31 mV/cycle) is greatly reduced by the quadruple modification of Eu. The charge compensation mechanism, phase structure transition pattern, anion behavior and CEI evolution are analyzed by a series of ex-situ methods. The simple modification method provides guidance for the overall improvement of the performance of lithium-rich cathode materials.

State-of-Charge Estimation of Lithium-Rich Manganese-Based Batteries Based on WOA LSTM and Extended Kalman Filter

Recent years, electric vehicles gradually become popular, but their cruising range has become one of the main problems that plague car companies and users. The lithium-rich manganese-based cathode material batteries with higher energy density stand out. The state of charge is an important parameter. This paper selects a 19Ah lithium-rich manganese-based cathode material battery for research, using extended Kalman filter based on second-order Equivalent circuit model estimate its state of charge. However, the impedance spectrum of lithium-rich manganese battery is different from that of 18650 lithium-ion battery, and the second-order equivalent circuit model will have errors, resulting in the low accuracy of SOC estimation. In order to solve this problem, this paper proposes two schemes: EKF-LSTM and LSTM-EKF. The whale optimization algorithm (WOA) is used to select the preset parameters. The results show that the LSTM-EKF method has the highest estimation accuracy, with a maximum error of 1.46%.

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.