Lithium-rich Cathode Materials Research Articles

A universal strategy towards high-rate and ultralong-life of Li‐rich Mn‐based cathode materials

Lithium-rich manganese-based cathode materials (LRMs) have shown promise for the next-generation lithium battery cathodes due to their high discharge specific capacity (∼250 mAh g−1) and wide operating voltage range (2.0–4.8 V). However, these materials face limitations such as low initial Coulombic efficiency (ICE), poor cycle stability, and inadequate rate capability. To address these challenges, we employed a simple citric acid treatment (CA-treatment) method to fabricate the Li-rich spinel coating layer on LRMs. This in situ formed spinel Li4Mn5O12 layer successfully suppresses the oxygen release, provides three-dimensional (3D) lithium-ion diffusion channels and enriches Li embedding sites, resulting in a substantial improvement in the rate capability and high-rate cycling performance. The modified LRM delivers a high specific capacity of 193.7 mAh g−1 at 2.0 C and 154.8 mAh g−1 at 5.0 C, after 1000 cycles at 10.0 C, 77.4 % capacity retention with 102.5 mAh g−1 is realized. This facile CA-treatment benefits the electrochemical properties of LRMs comparable to those of altering the microscopic morphology. This work offers a new avenue for exploring outstanding LRMs with high-rate and ultralong cycling life.

Enhanced electrochemical properties of Li1.2Mn0.54Co0.13Ni0.13O2 by modulation of surface oxygen vacancies

The lithium-rich cathode material Li1.2Mn0.54Co0.13Ni0.13O2 (LMR) has attracted significant interest due to its high specific capacity and energy density, which stem from its unique anionic redox chemistry. Oxygen vacancies significantly impact the crystal structure and electrochemical performance of Li-rich manganese-based cathode materials. This study thoroughly examined how sintering temperature affects the crystallinity, morphology, crystal structure, and oxygen vacancy content of the materials, as well as the impact of oxygen vacancies on their structural and electrochemical properties. XPS and EPR analyses are conducted to investigate the relationship between sintering temperature and oxygen vacancies. Additionally, the spinel phase, altered by oxygen vacancies on the material's surface, is identified using Raman, TEM and EELS. Furthermore, first-principles calculations and data from the constant-current intermittent titration technique indicate that oxygen vacancies significantly enhance the material's ion transport rate.

Multifunctional surface modification to enhance the electrochemical performance of lithium-rich manganese-based cathode materials

The preparation of high-performance lithium-rich manganese-based cathode materials (LLOs) require attention to the redox of anions and the migration of transition metals (TM) during the cycling process. In this study, Ce ion-doped Li-rich cathode coated with La0.2Ce0.8O2, which has abundant oxygen vacancies on its surface, was prepared. The presence of the oxygen storage material La0.2Ce0.8O2 can effectively absorb the irreversible oxygen generated during cycling, preventing it from reacting with the electrolyte to form thick cathode electrolyte interface (CEI) coatings. These coatings hinder the relative activity of lattice oxygen in the bulk phase, reducing the specific capacity of the material. Additionally, the 5d metal ion Ce carries a large nuclear charge, causing a 'pinning effect' when it integrates into the LLOs structure. This effect reduces thermal oscillation in the lattice, impedes TM migration during battery charging and discharging, and effectively prevents voltage decay. Results indicate that after 100 cycles at 1C and 25 °C, the surface-coated materials maintain a discharge-specific capacity of 194 mAh/g, compared to 158 mAh/g for uncoated material. Voltage decay decreased from 4.4 mV/cycle to 1.8 mV/cycle, with an ICE of 91.5 % versus the original material's 82.8 %. The modified material also exhibits improved rate performance, retaining a specific capacity of 162 mAh/g at 3C, in contrast to the original material's 123 mAh/g.

Jointly Improving Anionic-Cationic Redox Reversibility of Lithium-Rich Manganese-Based Cathode Materials by N Surface Doping.

The lithium-rich manganese-based layer oxide (LRMO) with high specific capacity (∼300 mAh g-1) and economic feasibility is accepted as the cathode material for high energy density rechargeable batteries. Accompanied by the additional anionic redox reactions during the initial charging process, LRMO presents oxygen release, sluggish Li+ diffusion, and irreversible transition metal ion (TM) migration, which is responsible for its severe structural deterioration and rapid capacity/voltage decay. Here, the N doping strategy is proposed via feasible treatment of oxygen-vacancy-containing Li1.16Ni0.21Mn0.63O2-δ (LNMO) particles. The as obtained LNMO-N samples demonstrate doping N, partially reduced Mn/Ni cations, and oxygen vacancies on the surface. The DFT calculations and experimental results demonstrate that N replacing the crystal oxygen sites on the surface reduces the energy barrier for diffusion, thereby enhancing the kinetics of Li+ diffusion and improving the reversibility of transition metal migration. Furthermore, N doping induces stacking faults and a more flexible structure. Therefore, LNMO-N exhibits a significantly improved anionic-cationic redox reaction reversibility with a high discharge specific capacity of 296.6 mAh g-1 at 20 mA g-1 within the range of 2.0 to 4.8 V and an impressive initial Coulombic efficiency of 85.9%. Moreover, the rate capability is obviously improved with a remarkable capacity of 215.1 mAh g-1 at 200 mA g-1 in 200 cycles with a capacity retention of 72.52% and exceptional performance of 141.4 mAh g-1 even at a higher current density of 1000 mA g-1.

Mitigating chain degradation of lithium-rich manganese-based cathode material by surface engineering

Due to offering joint cationic and anionic redox, lithium-rich manganese-based layered oxides (LMLOs) allow high energy density in lithium-ion batteries. However, the oxygen loss, electrode-electrolyte interface side reactions and the structural degradation have resulted in continuous performance decay, hindering the scale-up application of LMLOs. Here, Li1.3V0.94(BO3)2 (LVB) is uniformly coated on the Li1.2Mn0.54Co0.13Ni0.13O2 (LMNCO) surface by using a sol-gel method combined with a high-temperature calcination. By applying multiple characterizations including in-situ XRD, DEMS, HRTEM, AFM and electrochemical test, we prove that the LVB layer provides a physical barrier, which effectively inhibits the surface reactivity and blocks the chain degradation from the source, improves the reversibility of O2- redox and prevents the phase transition and structural degradation propagating from the surface to the bulk. Moreover, the kinetic investigations and calculations reveal that the LVB modification not only improves the electron conductivity of materials by decreasing the surface work function and increasing the electron density near the Fermi energy level, but also provides expanded pathways with lower impedance to facilitate the Li+ transfer and diffusion. Impressively, the modified cathode exhibits the higher rate performance (151 mAh g-1 at 5C) and improved cycle stability under high cutoff voltage (217.7 mAh g-1 after 200 cycles at 0.2C in 2.0–4.8 V, 92.5 % capacity retention; even in 2.0–5 V, 93.9 % after 100 cycles). This work systematically investigates the inhibiting degradation mechanism and establishes the correlation between the intrinsic structure and surface engineering, and offers valuable insight into the development of high-performance LMLOs.

Cut-off voltage influencing the voltage decay of single crystal lithium-rich manganese-based cathode materials in lithium-ion batteries

The voltage decay of Li-rich layered oxide cathode materials results in the deterioration of cycling performance and continuous energy loss, which seriously hinders their application in the high-energy–density lithium-ion battery (LIB) market. However, the origin of the voltage decay mechanism remains controversial due to the complex influences of transition metal (TM) migration, oxygen release, indistinguishable surface/bulk reactions and the easy intra/inter-crystalline cracking during cycling. We investigated the direct cause of voltage decay in micrometer-scale single-crystal Li1.2Mn0.54Ni0.13Co0.13O2 (SC-LNCM) cathode materials by regulating the cut-off voltage. The redox of TM and O2− ions can be precisely controlled by setting different voltage windows, while the cracking can be restrained, and surface/bulk structural evaluation can be monitored because of the large single crystal size. The results show that the voltage decay of SC-LNCM is related to the combined effect of cation rearrangement and oxygen release. Maintaining the discharge cutoff voltage at 3 V or the charging cutoff voltage at 4.5 V effectively mitigates the voltage decay, which provides a solution for suppressing the voltage decay of Li-rich and Mn-based layered oxide cathode materials. Our work provides significant insights into the origin of the voltage decay mechanism and an easily achievable strategy to restrain the voltage decay for Li-rich and Mn-based cathode materials.

Durable Sb/Na co-doped lithium-rich cathode material prepared by a novel planetary griding method

Nano-sized cathode materials are recognized for their enhanced active reaction area and uniform chemical composition, leading to distinct electrochemical performance benefits. However, the conventional sol–gel methods used for nanomaterial synthesis are often marred by significant raw material wastage and lengthy preparation processes, limiting their practicality. This study introduces a straightforward planetary grinding approach using low-melting-point precursors for the synthesis of oxide cathodes for lithium batteries. Through this method, an antimony and sodium co-doped lithium-rich layered oxide was produced, showcasing an impressive specific capacity of 238.48 mAh/g at a current density of 0.2 C (50 mA/g). Furthermore, this material exhibited outstanding cycle performance, maintaining 97.5 % capacity retention after 500 cycles at 1 C, with a specific capacity of 190.54 mAh/g in the final cycle.

Cation doping for enhanced layer spacing and electrochemical performance in Li-rich Mn-based lithium-ion cathode materials

Lithium-rich manganese-based cathode materials offer promising research avenues owing to their high capacity. This study delved into the impact of cation doping on Li1.2Ni0.13Co0.13Mn0.54O2(LNCMO). A range of layered Li1.2BXNi0.13Co0.13Mn0.54O2 (LNCMOxB, B = Ca, Na, Al) cathode materials were produced utilizing calcium, sodium, and aluminum chloride as dopants. Combining these elements with the lithium-rich materials improves the capacity retention of the positive electrode and mitigates voltage decay. X-ray diffraction analysis, Rietveld structural refinement, SEM, and XPS verified the inclusion of Ca, Na, and Al in the synthesized samples. Electrochemical analysis revealed that the LNCMO-0.01Na sample, possessing the largest dopant radius, exhibited favorable cyclic stability at 0.2C. Conversely, the LNCMO-0.01Al sample, featuring the smallest doped cation radius, demonstrated superior rate performance. Specifically, after 30 cycles at varying rates, the capacity reached 170 mAh·g−1 at 0.2C. The LNCMO-0.007Ca sample exhibited the highest residual capacity, maintaining 151.4 mAh·g−1 after 100 cycles at 0.2C. Doping Li sites in Li1.2Ni0.13Co0.13Mn0.54O2 materials with appropriately sized divalent cations significantly enhances their overall electrochemical performance. This enhancement is attributed to ion doping within the Li and TM layers, expediting the diffusion kinetics of Li ions, and augmenting ion and electronic conductivity. Investigating the doping modification of lithium-rich manganese-based oxide microspheres is instrumental in advancing positive electrode materials for lithium-ion batteries, aiming for increased specific capacity and more stable material structures.

Enhancing electrochemical performance of lithium-rich manganese-based cathode materials through lithium sulfate coating

Enhancing electrochemical performance of lithium-rich manganese-based cathode materials through lithium sulfate coating

Double gradient coupling heterostructure design accurately regulates the anion process of the Li-rich cathode

Lithium-rich layered oxides are regarded as the next generation of cathode materials for lithium-ion batteries due to their high capacity and high operating voltage. However, the release of oxygen at high voltage has caused serious failure problems, severely limiting the commercial application of lithium-rich cathode materials. As the irreversible release of oxygen occurs first at the surface of the particles, the change in structure at the surface is also more drastic. In response to the variability of anion redox processes from surface to interior in the particles, a coupling strategy of Al, oxygen vacancies double gradient and spinel heterostructure was designed. The high concentration of oxygen vacancies and Al on the surface inhibits excessive oxidation of lattice oxygen and oxygen release. The surface heterostructure improves the reaction kinetics and increases the activity and reversibility of the electrode process. The concentration of oxygen vacancies and Al in the interior ensures highly active anionic redox and further enhances structural stability. The specific capacity (0.13 mAh/g/cycle) and voltage (1.34 mV/cycle) decay of the modified material is greatly reduced. In-situ and ex-situ characterisations were used to analyse the modification mechanism, which can effectively guide the improvement of lithium-rich cathode material performance.

Mitigating Strain Accumulation in Li2RuO3 via Fluorine Doping.

Lithium ruthenium oxide (Li2RuO3) is an archetypal lithium rich cathode material (LRCM) with both cation and anion redox reactions (ARRs). Commonly, the instability of oxygen redox activities has been regarded as the root cause of its performance degradation in long-term operation. However, we find that not triggering ARRs does not improve and even worsens its cyclability due to the detrimental strain accumulation induced by Ru redox activities. To solve this problem, we demonstrate that F-doping in Li2RuO3 can alter its preferential orientation and buffer interlayer repulsion upon Ru redox, both of which can mitigate the strain accumulation along the c-axis and improve its structural stability. This work highlights the importance of optimizing cation redox reactions in LRCMs and provides a new perspective for their rational design.

Construction of rod-like micro/nano structure and its effects on the electrochemical energy storage performance of lithium-rich manganese-based cathode material

Construction of rod-like micro/nano structure and its effects on the electrochemical energy storage performance of lithium-rich manganese-based cathode material

Influence of Li Content on the Topological Inhibition of Oxygen Loss in Li-Rich Cathode Materials.

Lithium-rich layer oxide cathodes are promising energy storage materials due to their high energy densities. However, the oxygen loss during cycling limits their practical applications. Here, the essential role of Li content on the topological inhibition of oxygen loss in lithium-rich cathode materials and the relationship between the migration network of oxygen ions and the transition metal (TM) component are revealed. Utilizing first-principles calculations in combination with percolation theory and Monte Carlo simulations, it is found that TM ions can effectively encage the oxidized oxygen species when the TM concentration in TM layer exceeds 5/6, which hinders the formation of a percolating oxygen migration network. This study demonstrates the significance of rational compositional design in lithium-rich cathodes for effectively suppressing irreversible oxygen release and enhancing cathode cycling performance.

Evolution Path of Precursor-Induced High-Temperature Lithiation Reaction during the Synthesis of Lithium-Rich Cathode Materials.

High-temperature lithiation is one of the crucial steps for the synthesis of Li- and Mn-rich layered metal oxide (LMLO) cathodes. A profound insight of the micromorphology and crystal structure evolution during calcination helps to realize the finely controlled preparation of final cathodes, finally achieving a desired electrochemical performance. In this work, two typical precursors (hydroxide and oxalate) were selected to prepare LMLO. It is found that the influence of the lithium source on reaction pathways is determined by the properties of precursors. In the case of hydroxide as a precursor, whatever lithium sources it is, the flake morphology of LMLO is inherited from hydroxide precursors. This is because the crystal structure of cathode products has a high similarity with its precursor in terms of the oxygen array arrangement, and the topological transformation occurs from hydroxide (P-3ml) to LMLOs (C/2m and R3m). Thus, the morphology and microstructure of LMLO cathodes could be well controlled only by tuning the properties of hydroxide precursors. Conversely, the decomposition of a lithium source has a great influence on the intermediate transformation when oxalate is used as the precursor. This is because a large amount of CO2 is released from the oxalate precursor after the decomposition reaction, resulting in drastic structural changes. At this time, the diffusion ability of the lithium source leads to the competition between the spinel phase and layered phase. Based on this point, the formation of a spinel intermediate phase can be reduced by accelerating the decomposition of the lithium source, contributing to the generation of a highly pure layered phase, thus exhibiting higher electrochemical performance. These insights provide an exciting cue to the rational selection and design of raw materials and lithium sources for the controlled synthesis of LMLO cathodes.

Performance improvement of Li-rich Mn-based materials with the submicron-sized single-crystal morphology and cationic doping

Lithium-rich manganese-based cathode materials (LRMCs) can be regarded as one of the most potential cathode materials for the next-generation high-energy Li-ion batteries due to the extra oxygen redox, which can greatly increase the actual output energy density of LRMCs. Nevertheless, the structure degradation and inevitable loss of oxygen will be triggered by the irreversible oxygen redox, which will cause a significant decline in cyclic performance and limited initial Coulombic efficiency, thus restricting their industrial applicability. Herein, the LRMCs with the submicron-sized single-crystal morphology and sodium doping are prepared by molten salt treatment with NaCl. On one hand, the submicron-sized single-crystal cathode effectively reduces the diffusion path for Li+ due to the smaller particle dimensions. On the other hand, Na+ doping expands the Li slab spacing, promoting the transport of Li+. The results show that the as-prepared material can purposefully alleviate oxygen release, improve structure stability, and increase the Li+ diffusion rate for the pristine LRMCs. Moreover, the as-prepared material in this study exhibits a higher reversible capacity of 282.8 mAh g−1 at 0.1 C and displays good cyclic performance, retaining a capacity rate of 80.9% after 200 cycles at 1 C. Therefore, this study offers a potential exploration for designing LRMCs with high energy density and excellent cyclic performance, which are achieved through building submicron-sized single-crystal morphology and introducing cationic doping.

Modification of lithium-rich manganese-based cathode materials by continuous coating formed by surface treatment of sodium dodecyl sulfate to improve electrochemical performance

With the development of new energy devices, the demand for electrode materials with high energy density (> 400 Wh/kg) is increasing day by day. Lithium-rich manganese-based cathode materials (LRMC) which meet the requirements are considered one of the most promising materials for the next generation of lithium-ion batteries, and have attracted wide attention. However, LRMC still faces some key scientific problems that need to be addressed, such as interface side reactions, poor rate performance, rapid voltage and capacity attenuation, and low first coulomb efficiency. The continuous Na2SO4-coated lithium-rich manganese-based cathode material Li1.2Ni0.13Co0.13Mn0.54O2 (S-LRMC) was synthesized using sodium dodecyl sulfate (SDS). SDS is composed of hydrophobic aliphatic hydrocarbon groups and hydrophilic sulfate carboxyl groups, so it can form a micelle-like coating on the surface of LRMC materials in aqueous solution. The uniform Na2SO4 coating formed after calcination can effectively inhibit the side reaction between electrode material and electrolyte and reduce the dissolution of transition metal ions. As a result, capacity retention, rate performance and discharge specific capacity are improved. After 100 cycles at 1 C, the specific discharge capacity of 4% S-LRMC is 187.8 mAh g−1 (LRMC is 138.3 mAh g−1), and the capacity retention is 87.35%. Even at a high current density of 5 C, the material still has a specific discharge capacity of 143.6 mAh g−1, which proves that the electrochemical performance of the material is excellent. Therefore, this study provides a new solution for improving the structural stability and electrochemical performance of lithium ion batteries.

PO43--doped layer @ spinel @ rGO sandwich-structured lithium-rich manganese-based cathode material with enhancing rate capability and cycle stability for Li-ion battery

The Li-rich Mn-based cathode (LRM) material faces challenges like low initial coulombic efficiency (ICE) and reduced capacity retention, which limit their commercial viability in high energy density lithium-ion batteries (LIBs). These challenges primarily arise from the irreversible migration of transition metal ions (TMn+) and the escape of lattice oxygen. Herein, this study proposes a novel approach to enhance Li-rich cathodes by implementing a PO43--doped layer @ spinel @ rGO sandwich structure, which effectively addresses the aforementioned challenges. Through the synergistic effects of PO43- doping and rGO surface modification, the modified samples demonstrate remarkable electrochemical properties. These include an impressive initial coulombic efficiency (ICE) of 87.54%, and a superior capacity of 187.12 mAhg−1 and 149.44 mAhg−1 at 25°C and 45°C, respectively, following 200 cycles at 1 C. Additionally, they exhibit an outstanding rate capability of 82.3 mAhg−1 at 10 C and a minimal voltage decrease of 0.504 V after 200 cycles. The synergetic strategy presented in this work serves as an inspiring source for the exploration of high energy density and long-cycle cathode materials.

A high-efficient stable surface-prelithiated Li1.2Ni0.13Co0.13Mn0.54O2 cathode enabled by sacrificial lithium nitrides for high-energy-density lithium-ion batteries

Lithium-rich cathode materials with superior practical specific capacity over 250 mAh g−1 are considered as one of the resolutions for high-energy-density lithium-ion batteries, while the intrinsic capacity loss caused by solid electrolyte interface (SEI) formation on the anode impedes the increase of energy density. To address this issue, we propose a composite cathode prelithiation strategy including a carbon-incorporated lithium phosphorus oxynitride (LiCPON) layer and a sacrificial Li3N (Sac. Li3N) layer, which can not only compensate for the capacity loss effectively and controllably with a high lithium utilization rate over 85% but also provide outstanding atmosphere stability with an 80.2% lithium utilization rate after exposed in dry air for 8 hours. The energy densities achieve 489.5 Wh kg−1 and 497.3 Wh kg−1 initially after cathode prelithiation in full cells paired with Si/C and SiOx/C anodes, corresponding to a 11.9% and 11.6% increase, respectively. The energy densities still remain 318.7 Wh kg−1 and 319.7 Wh kg−1 after 50 cycles with an increase of 13.7% and 11.7%, respectively. The cathode electrolyte interface (CEI) and SEI layers are mutually optimized and the electrolyte adsorption and degradation are suppressed after cathode prelithiation. Our work has demonstrated that such a composite cathode prelithiation strategy provides the possibility for large-scale industrial production, transportation, and conservation of prelithiated lithium-rich cathodes to achieve high-energy-density lithium-ion batteries.

Self-constructing a lattice-oxygen-stabilized interface in Li-rich cathodes to enable high-energy all-solid-state batteries

A lattice-oxygen-stabilized interface is formed in situ by the interaction of indium and oxidized lattice oxygen in the interface of Li2RuO3 (LRO) and Li3InCl6 (LIC), mitigating the irreversible lattice oxygen loss and stabilizing the surface structure.

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.