Lithium-rich Layered Oxide Cathode Materials Research Articles

Effects of Lithium Source and Content on the Properties of Li-Rich Layered Oxide Cathode Materials

Lithium-rich layered oxide (LLO) are considered high-capacity cathode materials for next-generation lithium-ion batteries. In this study, LLO cathode materials were synthesized via the hydroxide coprecipitation method followed by a two-step lithiation process using different lithium contents and lithium sources. The effects of lithium content and lithium source on structure and electrochemical performance were investigated. This study demonstrated the clear impact of Li/TM ratio on electrochemical performance. Lower Li/TM ratio reduced the irreversible capacity loss in the first cycle and provided better cycling stability among all samples. The best results exhibited an initial discharge capacity of 279.65 mAh g−1 and reached a discharge capacity of 231.9 mAh g−1 (82.9% capacity retention) after 30 cycles. The sample using Li2CO3 as lithium source exhibits better electrochemical performance than the sample using LiOH as lithium source. Therefore, it is important to choose the appropriate lithium source and optimal lithium content for improving structural properties and electrochemical performance of LLO.

A propanesultone-based polymer electrolyte for high-energy solid-state lithium batteries with lithium-rich layered oxides

A propanesultone-based polymer electrolyte with high ion transference number of ∼0.78 and wide electrochemical stability window of ∼5.0 V has been designed for solid-state lithium batteries with lithium-rich layered oxide cathode materials.

Stabilizing structure and voltage decay of lithium-rich cathode materials

A major challenge in the discovery of high-energy lithium-ion batteries (LIBs) is to control the voltage stability and Li+ kinetics in lithium-rich layered oxide (LrLO) cathode materials. Although these materials can provide a higher specific capacity compared to the current industrially used cathodes, the substantial voltage decay and low Li+ diffusion during long term cycling is a serious reason for hindering their practical applications. In order to suppress the voltage decay in lithium-rich cathode materials, herein we introduce the Ti doping into Li1.2Mn0.56Ni0.17Co0.07O2 cathodes. Also, the influence of Ti doping on the crystalline internal structure, surface chemistry, cycling retention, and Li+ kinetics of Li1.2Mn0.56Ni0.17Co0.07O2 cathodes have been focused in this work. The Ti doping effectively enhances the structural/interfacial stability of the cathode and accelerates the Li+ kinetics by expanding the lattice, thereby significantly realizing its voltage/cycling stability and high-rate capability. Experimental results show that Ti-doped LrLO (1% Ti) has achieved high electrochemical kinetics as the discharge cycle retention increased from 61.58% (pristine) to 80.0% after 180 cycles at 1 C, with 150.3 mAh g−1 showing superior high-rate performance at 5C. Ex-situ XRD results confirmed the better structural stability of Ti-doped LrLO after high-rate electrochemical cycling. Our findings provide a suitable element doping strategy for regulating the voltage decay and cycle retention of LrLO, thus promoting their real-world application in future batteries.

Suppression and Mechanism of Voltage Decay in Sb-Doped Lithium-Rich Layered Oxide Cathode Materials.

Voltage decay during cycling is the major problem for lithium-rich layered oxide cathodes. Here, we designed Sb-doped lithium-rich layered oxides prepared by a coprecipitation-solvent thermal method, aiming to alleviate the voltage decay of lithium-rich layered oxides. The midpoint discharge voltage and specific capacity of Li1.20Ni0.133Co0.133Mn0.633Sb0.01O2 (LLMO-Sb1) demonstrate almost no decaying after 100 cycles at 1 C. Moreover, it exhibits a large rate capacity (215 mAh g-1 at 5 C). The suppressed voltage decay and enhanced cycle performance of Sb-doped material are attributed to the high Sb-O bond energy, which can enhance the stability of the layered structure and suppress the layered-to-spinel phase transition. Moreover, Sb doping improves the rate capacity by reducing the energy barrier of lithium ion diffusion. This work opens a gate to prevent the oxidation of superoxo and peroxo, stabilizing the layered structure by selecting an element with a suitable radius and electronegativity.

Unravelling the Influence of Synthetic Paths on the Cation Arrangement in Lithium-rich Layered Oxide Cathode Materials

• The strategy for adjusting the cation arrangement of the Li-rich cathode materials was proposed by simply adjusting the mixing order of cations in the sol-gel synthesis. • The results further prove that improving the order arrangement of cations can effectively ameliorate the stability and electrochemical performance of the Li-rich materials. • The optimized Li-rich materials exhibit a good cycle performance with a capacity retention of 71.7% after 150 cycles, much better than that of the pristine sample with a retention of only 45.5%. Lithium-rich layered oxides (LLOs) have garnered substantial attention due to their superior reversible capacity. However, oxygen release and transition metal migration are likely to occur during the charging and discharging process because of the inherently unstable structure of LLOs, which hampers their commercialization process. Present studies suggest that the local structure and atomic arrangement have a considerable impact on the stability of LLOs. Hence, researchers have been trying to determine how to implement the control of atomic ordering. Herein, we propose a new strategy to modify the cation arrangement of LLOs by adjusting the mixing order of cations through the sol-gel method. As a result, the optimized S-LLO sample presents a more ordered cation arrangement than that of the pristine M-LLO sample. The S-LLO cathode, meanwhile, provides a high discharging capacity of 249.5 mAh·g −1 accompanied by a coulombic efficiency of 73.7% at 0.1 C and can still maintain a capacity of 91.8 mAh·g −1 at 10 C. More importantly, a high-capacity retention of 71.7% can be obtained after 150 cycles at 1 C for the optimized LLO cathode, whereas the pristine M-LLO sample retains a retention of only 45.5%. A new strategy to modify the cation arrangements of LLOs by adjusting the mixing order of cations through the sol-gel method.

Improving the Electrochemical Performance of Lithium-Rich Cathode Materials by Vanadium and Titanium Co-Doping Using Solution Combustion Synthesis

Abstract A lithium-rich layered oxide cathode material (Li1.2[Mn0.54Ni0.13Co0.13]O2) was synthesized using solution combustion synthesis, and the electrochemical effects of co-doping with vanadium and titanium were studied. Materials analysis showed that layered oxides with an α-NaFeO2 structure, spherical morphology, and particle size distribution between 0.4 and 1 µm were synthesized. Electrochemical experiments (charge–discharge tests) also indicated that the presence of vanadium in the cathode structure increases its specific capacity to 257.6 mAh/g and improves rate capability and cyclic performance. Increasing the amount of titanium in the cathode improves cyclability; however, it also decreases specific capacity. The latter occurs because titanium is not electrochemically active, meaning it does not participate in redox reactions. Also, increasing the amount of titanium beyond 0.02 mol leads to a considerable decrease in the rate capability.

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.

Surface Grafting SiO2 on Lithium-Rich Layered Oxide Cathode Material for Improving Structural Stability

Surface grafting of SiO2 layer was carried out to alleviate the intrinsic issues of lithium-rich layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 (LRLC). After analyzing the pristine and SiO2 coated samples by XRD, XPS, SEM and TEM characterizations, it is found that the surface of LRLC cathode material is successfully decorated with SiO2 layer while maintaining the pristine structure and morphology. The introduction of SiO2 coating prevents the erosion of cathode material from the electrolyte and inhibits the formation of spinel structure. More importantly, the capacity retention of the optimized 0.25 wt.% SiO2-coated LRLC sample after 200 cycles at 1 C delivers as high as 89.7%, much higher than that of the pristine sample (74.2%). There are obvious cracks on the surface of pristine sample after 200 cycles, while the surface of SiO2-coated LRLC samples remains intact, which convincingly proves that SiO2 layer can substantially promote the structural stability of cathode material. As last, the modification mechanism of SiO2 layer in the layered cathode material is elucidated. All in all, the shielding and scavenging effects of SiO2 protective layer towards HF hinder the electrolyte from corroding the cathode material, and improve the electrochemical performances, especially structure stability of the cathode material.

Dual-Site Doping Strategy for Enhancing the Structural Stability of Lithium-Rich Layered Oxides.

Lithium-rich layered oxide (LLO) cathode materials are considered to be one of the most promising next-generation candidates of cathode materials for lithium-ion batteries due to their high specific capacity. However, some inherent defects of LLOs hinder their practical application due to the oxygen loss and structure collapse resulting from intrinsic anion and cation redox reactions, such as poor cycle stability, sluggish Li+ kinetics, and voltage decay. Herein, we put forward a facile synergistic strategy to respond to these shortcomings of LLOs via dual-site doping with cerium (Ce) and boron (B) ions. The doped Ce ions occupy the octahedral sites, which not only enlarge the cell volume but also stabilize the layered framework and introduce abundant oxygen vacancies for LLOs, while B ions occupy the tetrahedral sites in the lattice, which block the migration path of transition metal (TM) ions and reduce the oxygen loss using the strong B-O bond. Based on this dual-site doping effect, after 100 cycles at 1 C, the dual-site doped materials exhibit excellent structural stability with a capacity retention of 91.15% (vs 75.12%) and also greatly suppress the voltage decay in LLOs with a voltage retention of 93.60% (vs 87.83%).

Soft X-ray Transmission Microscopy on Lithium-Rich Layered-Oxide Cathode Materials

Energy-dependent full field transmission soft X-ray microscopy (TXM) is able to give a full picture at the nanometer scale of the chemical state and spatial distribution of oxygen and other elements relevant for battery materials, providing pixel-by-pixel absorption spectrum. We show different methods to localize chemical inhomogeneities in Li1.2Mn0.56Ni0.16Co0.08O2 particles with and without VOx coating extracted from electrodes at different states of charge. Considering the 3d(Mn,Ni)-2p(O) hybridization, it has been possible to discriminate the chemical state of Mn and Ni in addition to the one of O. Different oxidation states correspond to specific features in the O-K spectra. To localize sample regions with specific compositions we apply two different methods. In the first, the pixel-by-pixel ratios of images collected at different key energies clearly highlight local inhomogeneities. In the second, introduced here for the first time, we directly correlate corresponding pixels of the two images on a xy scatter plot that we call phase map, where we can visualize the distributions as function of thickness as well as absorption artifacts. We can select groups of pixels, and then map regions with similar spectral features. Core-shell distributions of composition are clearly shown in these samples. The coating appears in part to frustrate some of the usual chemical evolution. In addition, we could directly observe several further aspects, such as: distribution of conducting carbon; inhomogeneous state of charge within the electrode; molecular oxygen profiles within a particle. The latter suggests a surface loss with respect to the bulk but an accumulation layer at intermediate depth that could be assigned to retained O2.

Local structure modulation via cation compositional regulation for durable Li-rich layered cathode materials

A series of manganese-based lithium-rich layered oxide (LLO) cathode materials with different local structures have been synthesized by adjusting the stoichiometric ratios of Mn/Ni. One of the as-synthesized cathode materials with an Mn/Ni ratio of 7 to 2 (Li1.3Mn0.7Ni0.2Co0.1O2.4, denoted as MNC-721) showed an appropriate degree of cation mixing, thereby exhibiting superior cycling stability, better rate capability, and much slower voltage decay when compared with the other two cathode materials with different Mn/Ni ratios. More importantly, a full cell was assembled using the MNC-721 cathode material and it rendered mass-energy density retention of 90.0% after 300 cycles. An appropriate amount of mixing of the Li+ ions and the transition metal (TM) in the Li layers improved the electrochemical performance of the material. The TM ions in the lithium layers can support the layered structure as well as weaken the repulsion between neighboring oxygen layers during processes of charge and discharge. The proposed method in this project is promising to be used to improve LLO cathode materials’ electrochemical performance by modifying their local structures, thereby promoting their further practical applications in Li-ion batteries with high performance.

Challenges and solutions of lithium-rich manganese-based layered oxide cathode materials

Challenges and solutions of lithium-rich manganese-based layered oxide cathode materials

Li1.2Mn0.54Ni0.13Co0.13O2 nanosheets with porous structure as a high-performance cathode material for lithium-ion batteries.

The morphological and structural optimizations of electrode materials are efficient ways to enhance their electrochemical performance. Herein, we report a facile co-precipitation and subsequent calcination method to fabricate Li1.2Mn0.54Ni0.13Co0.13O2 nanosheets consisting of interconnected primary nanoparticles and open holes through the full thickness. By comparing the nanosheets and the agglomerated nanoparticles, the effects of the morphology and structure on the electrochemical performance are investigated. Specifically, the nanosheets exhibit a discharge capacity of 210 mA h g−1 at 0.5C with a capacity retention of 85% after 100 cycles. The improved electrochemical performance could be attributed to their morphological and structural improvements, which may facilitate sufficient electrolyte contacts, short diffusion paths and good structural integrity during the charge/discharge process. This work provides a feasible approach to fabricate lithium-rich layered oxide cathode materials with 2D morphology and porous structure, and reveals the relationships between their morphology, structure and electrochemical performance.

A Li-rich layered-spinel cathode material for high capacity and high rate lithium-ion batteries fabricated via a gas-solid reaction

Lithium-rich layered oxide (LLO) cathode materials have drawn extensive attention due to their ultrahigh specific capacity and energy density. However, their commercialization is still restricted by their low initial coulombic efficiency, slow intrinsic kinetics and structural instability. Herein, a facile surface treatment strategy via gaseous phosphine was designed to improve the rate performance and capacity stability of LLOs. During the solid-gas reaction, phosphine reacted with active oxygen at the surface of LLOs due to its reductivity, forming oxygen vacancies and spinel phase at the surface region. As a result, Li ion conductivity and structural stability were greatly enhanced. The phosphinetreated LLOs (LLO@P) showed a layered-spinel hybrid structure and delivered an outstanding rate performance of 156.7 mA h g−1 at 10 C and a high capacity retention of 74% after 300 cycles at 5 C.

Microwave-assisted hydrothermal synthesis of lithium-rich layered oxide cathode materials with high stability

Lithium-rich layered oxides have the advantages of high specific capacity (> 250 mAh g−1) and high energy density, which make them highly competitive in the lithium-ion cathode material market. However, low efficiency, poor cycle stability, and poor rate performance severely constrained their development. In this paper, the spherical lithium-rich Li1.2Mn0.54Ni0.13Co0.13O2 compound was rapidly synthesized by microwave hydrothermal method, and the microwave hydrothermal time was optimized. The samples were characterized and analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy (Raman), and X-ray photoelectron spectroscopy (XPS). The prepared lithium-rich compound is porous spherical secondary particles, of which the size distributed between 2.5 and 3.5 μm, which makes materials have larger specific surface area and active potential and promotes the improvement of electrochemical kinetics. The results of 100 charge-discharge cycles show that the microwave hydrothermal 40-min cathode has good stability, and the capacity retention rate can reach 91.4%. Furthermore, it can still provide a discharge capacity of 160.5 mAh g−1 at a current density of 5 C.

Enhanced electrochemical performance of lithium-rich layered oxide cathodes by a facile self-template method for lithium-ion batteries

Lithium-rich layered oxide cathode material Li1.2Ni0.13Co0.13Mn0.54O2 has been successfully synthesized via a self-template method followed with sol-gel reaction, microspheres consisting of three-dimensional (3D) nanothorn MnO2 are used as the template and Mn source. The as-prepared sample (denoted as LNCM-T) exhibits well-layered structure and high crystallinity, which is confirmed by XRD and HRTEM. The results of electrochemical performances show that the LNCM-T sample has excellent high-rate capability with a discharge capacity of 159.7 mA h g−1 at a current density of 1250 mA g−1. Besides, it delivers a high initial Coulombic efficiency of 84.3% with a discharge capacity of 243.8 mA h g−1 at room temperature. The remarkable cycling stability and excellent rate capability of LNCM-T sample are ascribed to the enhanced layered structural stability, short lithium-ion diffusion path and reduced charge transfer resistance.

In-situ generate spinel phase on a glucose-derived carbon-coated lithium-rich layered oxide cathode materials and its improved electrochemical performance

Lithium-rich layered oxide cathode material gains a great concern as a potential cathode material for high energy density lithium-ion batteries recently; however, the low coulombic efficiency and poor rate performance still impede its commercial applications. In this work, a Li-rich@spinel@carbon heterostructure cathode material was synthesized via a solvothermal method together with in situ synchronous carbonization-reduction method. The unique structure fabricates fast Li+ diffusion channels of in situ-generated spinel structure (Fd-3 m) and electrons highway of carbon coating on the surface of lithium-rich cathode materials. Corresponding to the high lithium-ion diffusion coefficient and electric conductive, the heterostructures’ cathode material delivers a high discharge capacity of 313.9 mAh g−1 at 0.2 C and superior rate performance of 186.1 mAh g−1 at 5 C. The dual protective layer of spinel phase and carbon also help to improve the capacity retention of the samples (which remains 227.3 mAh g−1 and a retention of 102.7% after 100 cycles at 1 C rate). This work opens up a new route in terms of the design and synthesis of multi-phase cathode electrode materials for high performance energy storage devices.

Stabilizing Li-rich NMC Materials by Using Precursor Salts with Acetate and Nitrate Anions for Li-ion Batteries

Lithium-rich layered oxide cathode materials of Li1.2Mn0.5100Ni0.2175Co0.0725O2 have been synthesized using metal salts with acetate and nitrate anions as precursors in glycerol solvent. The effects of the precursor metal salts on particle size, morphology, cationic ordering, and ultimately, the electrode performance of the cathode powders have been studied. It was demonstrated that the use of cornstarch as a gelling agent with nitrate-based metal salts results in a reduction of particle size, leading to higher surface area and initial discharge capacity. However, the cornstarch gelling effect was minimized when acetate salts were used. As observed in the Fourier-transform infrared spectroscopy analysis, cornstarch can react with acetates to form acetyl groups during the synthesis, effectively preventing the cornstarch gel from capping the particles, thus leading to larger particles. A tradeoff was found when nitrate and acetate salts were mixed in the synthesis. It was shown that the new cathode powder has the best cationic ordering and capacity retention, promising a much stable Li-rich cathode material for lithium-ion batteries.

Synthesis of lithium rich layered oxides with controllable structures through a MnO2 template strategy as advanced cathode materials for lithium ion batteries

The electrochemical performance of lithium ion batteries depend largely on the structural properties of electrode materials. In this work, we propose an approach to synthesize lithium-rich layered oxides (LLOs) materials using a manganese dioxide (MnO2) template strategy, which could control the structure and particle size of final products via choosing different MnO2 templates. Through precisely optimizing, we successfully prepare cross-linked nanorods (CLNs) and agglomerate microrods (AMs) Li1.2Ni0.15Co0.1Mn0.55O2 cathode materials by using carbon-decorated MnO2 nanowires and MnO2 nanorods as templates, respectively. The lithium ion battery based on the CLNs exhibits excellent performance, delivering a high capacity of 286.2 mAh g−1 at 0.1 C and 237.5 mAh g−1 at 1 C. In addition, the device remains 98% and 89% of its initial capacity after 50 cycles at 0.1 C and 100 cycles at 1 C, respectively. The remarkable electrochemical performance can be mainly attributed to the cross-linked nanorods structure which can provide relatively shorter lithium ion diffusion length, larger reaction surface and more internal cavity. This universal structure engineering strategy may shed light on new material structures for high performance lithium-rich layered oxide cathode materials.

Enhanced cycling stability of boron-doped lithium-rich layered oxide cathode materials by suppressing transition metal migration

Lithium-rich layered oxide (LLO) has been considered as an attractive candidate due to its high capacitive performance.