Layered Oxide Li1 Research Articles

LiVOPO4‐Modified Lithium‐Rich Layered Composite Cathodes for High‐Performance Lithium‐Ion Batteries

AbstractLi‐rich layered oxide Li1.2Ni0.13Co0.13Mn0.54O2 (LNCMO) is a promising cathode material for high‐energy‐density lithium‐ion batteries (LIBs). However, it suffers from severe capacity fading and voltage decay, especially at high voltage (>4.5 V). In this study, we successfully design an active LiVOPO4 (LVOP) coating on the LNCMO surface. The LNCMO/LVOP composites exhibit enhanced rate capability and largely improved cycling stability during long‐term cycling. Such superior performances can be attributed to the active LVOP coating layer, which can suppress the parasitic reactions between the LNCMO surface and the electrolyte. This work shows the potential for designing Li‐rich layered composite cathode materials by coating the active phase for high energy/power LIBs.

Controlled synthesis of Li1.17Ni0.21Mn0.54Co0.08O2 as a cathode material for Li ion batteries

Abstract Li-rich layered oxides Li1+xMO2 (M: Ni, Co, Mn) being a combination between Li2MnO3 and LiMO2, are considered as attractive high-capacity electrode materials for Lithium ion batteries. Here, we present the composition Li1.17Ni0.21Mn0.54Co0.08O2 with low cobalt content. The synthesis process was optimized by varying the pH of the co-precipitation step and pure phase was obtained only for pH = 11.3. The morphology of the material consists on the agglomeration of quasi-spherical particles an average particle size of 157 nm. The electrochemical properties of this electrode material were investigated, and a specific capacity of 250 mAh/g was recorded in the voltage range of 2–4.8 V. While the first charge process evidenced a potential plateau at 4.5 V corresponding to the oxygen redox activity, the subsequent electrochemical behavior is governed by Ni2+/Ni4+ and Co3+/Co4+ redox couples. When cycled for 40 charge/discharge cycles at 0.1C rate, the capacity retention is still good and remains around 85% with a coulombic efficiency of around 98%. The comparison of the obtained performances with those of existing Li-rich electrode materials show the excellent features of the studied Li-rich material for the next generation Lithium-ion batteries.

Enhanced electrochemical properties and thermal stability of Zr4+ doped Li1.20Mn0.54Ni0.13Co0.13O2 cathode material by a Li ion conductor of Li3PO4 surface coating

Li-excess layered oxide Li1.20Mn0.54Ni0.13Co0.13O2 and Li1.20Mn0.53Ni0.13Co0.13Zr0.01O2 were synthesized via a co-precipitation method, and then different contents of Li3PO4 were successfully coated on the surface of Li1.20Mn0.53Ni0.13Co0.13Zr0.01O2 by using the wet process. The influences of the Zr4+ doping and Li3PO4 coating on the crystal structures and particles morphology were systematically analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the Zr4+ doping enlarged the Li+ diffusion channel of the cathode structure and the 2 wt% Li3PO4 coated Li1.20Mn0.53Ni0.13Co0.13Zr0.01O2 was covered by the Li3PO4 coating layer with a thickness of 50 nm. The charge and discharge tests revealed that the Zr4+ doping and Li3PO4 coating could obviously enhance the electrochemical properties of cathode. Especially, the 2 wt% Li3PO4 coated Li1.20Mn0.53Ni0.13Co0.13Zr0.01O2 delivered a discharge capacity of 200.9 mAh g−1 after 300 cycles and the corresponding capacity retention is 92.1%. While only a discharge capacity of 163.7 mAh g−1 and a capacity retention of 83.9% are obtained after 300 cycles for the pristine Li1.20Mn0.54Ni0.13Co0.13O2. The Nyquist plots implied that the Zr4+ doping and Li3PO4 coating could effectively inhibit the increasing of the electrolyte/electrode interface charge transfer resistance during cycling.

Nonstoichiometry of Li-rich cathode material with improved cycling ability for lithium-ion batteries

Lithium-rich layered oxides are considered as promising cathode materials for lithium-ion batteries due to its high capacity, but the rapid decay of capacity and operating voltage are great challenges to achieve its commercial application. In this work, the nonstoichiometry of Li-rich layered oxide Li1.2Mn0.6Ni0.2O2 was designed by directly declining the Mn amounts in the form of Li1.2MnxNi0.2O2 (x = 0.59, 0.57, 0.55). The nonstoichiometric sample Li1.2Mn0.55Ni0.2O2 exhibits a capacity of 170.73 mAh g−1 at 0.5 C, a little lower than 187.29 mAh g−1 of Li1.2Mn0.6Ni0.2O2, however, better cycling stability of operating voltage and capacity is attained with the reduction of Mn amounts, compared to that of Li1.2Mn0.6Ni0.2O2. The capacity retention of Li1.2Mn0.55Ni0.2O2 is enhanced to 88.7% via 74.7% of Li1.2Mn0.6Ni0.2O2 after 100 cycles at 0.5 C. The declining value of operating voltage for Li1.2Mn0.55Ni0.2O2 is 0.200 V as compared to 0.559 V for Li1.2Mn0.6Ni0.2O2. X-ray photoelectron spectra (XPS) was employed to confirm the existence of Ni3+ in the nonstoichiometric samples, and the amounts of Ni3+ increase along the Mn contents decrease. The improvement of electrochemical properties for nonstoichiometric samples is attributed to the presence of Ni3+ due to Ni3+ can defer the transition of layered-to-spinel structure through decreasing the Li/Ni mixing.

Improved low-temperature performance of surface modified lithium-rich Li1.2Ni0.13Co0.13Mn0.54O2 cathode materials for lithium ion batteries

High capacity lithium-rich layered oxide Li1.2Ni0.13Co0.13Mn0.54O2 cathode material is considered as a most promising cathode material for lithium ion batteries. However, its application is greatly limited due to the characteristics of low initial coulombic efficiency and poor low-temperature performance. In this study, AlF3-coated Li1.2Ni0.13Co0.13Mn0.54O2 has been prepared via a facile wet chemical process. It is found that a dense AlF3 layer with a nanoscale thickness is covered on the surface of Li1.2Ni0.13Co0.13Mn0.54O2 particles, building a rapid lithium transport bridge for adjacent active materials and reducing side reaction between the electrolyte and active material. Compared to the pristine Li1.2Ni0.13Co0.13Mn0.54O2, 2% AlF3-coated sample exhibits higher discharge capacity and initial coulombic efficiency (86.7%). Meanwhile, 2% AlF3-coated sample displays obviously superior rate capability at 0 °C and higher capacity retention at −10 and −20 °C. The improvement of low-temperature performance can reasonably be attributed to the formation of the spinel structure and the LiAlO2 on the surface of the active materials, which can improve the electronic conductivity and lithium ion conductivity of the cathode material, respectively.

Li–Ti Cation Mixing Enhanced Structural and Performance Stability of Li‐Rich Layered Oxide

AbstractLi‐rich layered metal oxides are one type of the most promising cathode materials in lithium‐ion batteries but suffer from severe voltage decay during cycling because of the continuous transition metal (TM) migration into the Li layers. A Li‐rich layered metal oxide Li1.2Ti0.26Ni0.18Co0.18Mn0.18O2 (LTR) is hereby designed, in which some of the Ti4+ cations are intrinsically present in the Li layers. The native Li–Ti cation mixing structure enhances the tolerance for structural distortion and inhibits the migration of the TM ions in the TMO2 slabs during (de)lithiation. Consequently, LTR exhibits a remarkable cycling stability of 97% capacity retention after 182 cycles, and the average discharge potential drops only 90 mV in 100 cycles. In‐depth studies by electron energy loss spectroscopy and aberration‐corrected scanning transmission electron microscopy demonstrate the Li–Ti mixing structure. The charge compensation mechanism is uncovered with X‐ray absorption spectroscopy and explained with the density function theory calculations. These results show the superiority of introducing transition metal ions into the Li layers in reinforcing the structural stability of the Li‐rich layered metal oxides. These findings shed light on a possible path to the development of Li‐rich materials with better potential retention and a longer lifespan.

Surface modification of Li rich Li1.2Mn0.54Ni0.13Co0.13O2 cathode particles

Li-rich Mn-based layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 (LMNCO) has received great interest due to its high discharge capacity. However, the fast capacity attenuation seriously hinders its wide application. LMNCO particles are synthesized via a co-precipitation method. To enhance the cycle stability, (Ni0.4Co0.2Mn0.4)1-xTix(OH)2+2x surface layer is deposited on LMNCO precursor particles by a second co-precipitation process. Due to the mutual diffusion of elements during sintering, Ti is distributed in the 2–3 μm shell of particles. The cells are cycled in a voltage window of 2.0–4.8 V at 0.5C. After 200 cycles, LMNCO exhibits a capacity retention of 43%, and LMNCO particles have been pulverized by the cycle process. In contrast, the structural integrity of coated particles is maintained, and therefore the cycle stability is evidently improved.

Towards improved structural stability and electrochemical properties of a Li-rich material by a strategy of double gradient surface modification

The electrochemical properties of layered Li-rich oxide Li1.2Ni0.13Co0.13Mn0.54O2 (LLO) can be enhanced by a facile NaF surface modification. We have clarified by XPS, HR-TEM and HAADF-STEM analyses that the mechanism is the formations of a gradient coating layer Na1-xLixF and a gradient LLO surface Li1.2-xNaxNi0.13Co0.13Mn0.54O2 via a Li+/Na+ exchange reaction. The exchange reaction occurs at the Li-slabs of LLO down to a depth of less than 15 nm. After such a double gradient surface modification, the LLO displays markedly improved cycle life and rate capability as well as suppressed voltage decay. It exhibits a capacity retention of 85% beyond 1000 cycles at 10 C and a voltage decay of only 0.0021 V per cycle at 0.5 C, revealing great application prospects in energy storage materials.

Li1.233Mo0.467Fe0.3O2 as an advanced cathode material for high-performance lithium ion battery

Li-rich layered transition metal oxides show high reversible capacity in rechargeable lithium-ion batteries, as represented by the Li1.2Ni0.13Co0.13Mn0.54O2. However, it suffers from severe problems in practical applications such as voltage fading, poor cycle life and poor rate performance. Here, we reported a Li-rich layered oxide Li1.233Mo0.467Fe0.3O2 showing high reversible specific capacity of 262.9 mA h/g at the initial cycle and then up to 305.4 mA h/g after several cycles. The material shows decent capacity retention that after 25 cycles it still sustained a value of 257.8 mAh/g at the charge/discharge voltage range of 1.0–4.3 V. It is noticed that the capacity increase at 2.5 V platform is attributed to structural rearrangement at lower potential. The present work suggests choosing appropriate constituent stabilizing structures in Li-rich layered oxides should be an efficient strategy for designing advanced cathode materials.

Enhanced electrochemical performance of Li3V1.5Al0.5(PO4)3-modified Li1.12(Ni0.18Co0.07Mn0.57)O2 cathode for Li-ion batteries

Li-rich manganese-based cathode materials are very promising for rechargeable Li-ion batteries. In our task, the Li-rich layered oxides Li1.12(Ni0.18Co0.07Mn0.57)O2 (LLMO) are prepared via the method of co-precipitation and solid-state reaction. Li3V1.5Al0.5(PO4)3 (LVAP) is applied to modify the LLMO by the chemical deposition method. Successful coating of LVAP layer on the pristine LLMO surface is demonstrated by TEM and XPS. Notably, the initial coulombic efficiency of LVAP-modified LLMO is 93%, which is improved compared to 82% of the pristine LLMO. The modified electrode also achieves excellent cyclic stability, which retains 96% of capacity after 100 cycles while the pristine electrode only retains 75%. Moreover, in comparison to the 100 mAh g−1 capacity of pristine LLMO at 5C, the LVAP-modified LLMO provides a high discharge capacity of 176 mAh g−1. In conclusion, this paper has demonstrated that the surface modification with LVAP is dedicated to improving the cyclic performance and rate capability of Li-rich layered oxides.

Synthesis, microstructure, and electrochemical performance of Li-rich layered oxide cathode materials for Li-ion batteries

Li-rich layered oxides Li1.2Mn0.54Ni0.13Co0.13O2 were synthesized by modified Pechini method using various compositions of the reaction mixture. Difference in the electrochemical performance of cathodes on their basis is explained by different morphology and microstructure of the materials. The porous hierarchical structure favors a better electrochemical performance. The presence of defects, including crystal twins, in the samples is considered to be a major reason that leads to their poor cyclability and rate capability.

Surface Modification of Li1.2Mn0.54Ni0.13Co0.13O2 Cathode Material with Al2O3/SiO2 Composite for Lithium-Ion Batteries

Lithium-rich layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 is synthesized by solid phase method and followed by surface modification with 2 wt% nAl2O3/SiO2 (n means the molar ratio of Al2O3 and SiO2). The morphology, structure and electrochemical properties of the material samples before and after coating treatment are systematically investigated by X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, linear sweeping voltammetry, potentiostatic intermittent titration and electrochemical impedance spectroscopy. The results show that a protective multilayer is formed on the material particle surface with a new coating layer like Lix[AlySizO4] and an intermediate layer with lithium-deficient disordered spinel structure after annealing treatment. This multilayer can prevent the material from corrosion of the electrolyte deposition product, provide improved lithium ion transportation and suppress the evolution from layered structure to spinel. The coated samples present the improved initial coulombic efficiency, capacity retention, cycling stability, rate capability and reduced voltage decay compared to the pristine material and it delivers the best comprehensive electrochemical performance when the molar ratio of Al2O3 and SiO2 is 2:1. The main role of Al2O3 and SiO2 in coating for the improvements of the material performance is further discussed.

Surface modification with oxygen vacancy in Li-rich layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 for lithium-ion batteries

A couple of layered Li-rich cathode materials Li1.2Mn0.54Ni0.13Co0.13O2 without any carbon modification are successfully synthesized by solvothermal and hydrothermal methods followed by a calcination process. The sample synthesized by the solvothermal method (S-NCM) possesses more homogenous microstructure, lower cation mixing degree and more oxygen vacancies on the surface, compared to the sample prepared by the hydrothermal method (H-NCM). The S-NCM sample exhibits much better cycling performance, higher discharge capacity and more excellent rate performance than H-NCM. At 0.2 C rate, the S-NCM sample delivers a much higher initial discharge capacity of 292.3 mAh g−1 and the capacity maintains 235 mAh g−1 after 150 cycles (80.4% retention), whereas the corresponding capacity values are only 269.2 and 108.5 mAh g−1 (40.3% retention) for the H-NCM sample. The S-NCM sample also shows the higher rate performance with discharge capacity of 118.3 mAh g−1 even at a high rate of 10 C, superior to that (46.5 mAh g−1) of the H-NCM sample. The superior electrochemical performance of the S-NCM sample can be ascribed to its well-ordered structure, much larger specific surface area and much more oxygen vacancies located on the surface.

Fluorine-Doped Carbon Surface Modification of Li-Rich Layered Oxide Composite Cathodes for High Performance Lithium-Ion Batteries

Fluorine (F)-doped carbon modified lithium rich layered oxides Li1.2Mn0.54Ni0.13Co0.13O2 (LMCNO@C-F) are synthesized by a facile sol–gel process. In this constructed architecture, the F-doped carbo...

Multiple Linkage Modification of Lithium-Rich Layered Oxide Li1.2Mn0.54Ni0.13Co0.13O2 for Lithium Ion Battery.

A multiple linkage modification (MLM) method was investigated to comprehensively improve the properties of lithium-rich layered oxides. MLM Li1.2Mn0.54Ni0.13Co0.13O2 was successfully synthesized via continuous and appropriate heat treatment. The synthesized Li1.2Mn0.54Ni0.13Co0.13O2 particles were coated with a Li2ZrO3 layer and doped with Zr4+ by using a Zr compound as the MLM reagent. The Li2ZrO3 coating layer could protect materials from the corrosion of hydrogen fluoride, and the structure of the base materials was stabilized due to Zr4+ doping. In addition, the formation of Li2ZrO3 captured inactive residual lithium on the surface and absorbed lithium of host materials, thereby leading to the reduction in the Li/M ratio of materials and promoting the first-cycle Coulombic efficiency. The MLM material delivered the highest initial cycle Coulombic efficiency (∼85%), the best cycle and rate performance among bare and ZrO2-coated particles. These results indicate that MLM is an important technique for improving the performance of electrode materials.

Understanding voltage decay in lithium-excess layered cathode materials through oxygen-centred structural arrangement

Lithium-excess 3d-transition-metal layered oxides (Li1+xNiyCozMn1−x−y−zO2, >250 mAh g−1) suffer from severe voltage decay upon cycling, which decreases energy density and hinders further research and development. Nevertheless, the lack of understanding on chemical and structural uniqueness of the material prevents the interpretation of internal degradation chemistry. Here, we discover a fundamental reason of the voltage decay phenomenon by comparing ordered and cation-disordered materials with a combination of X-ray absorption spectroscopy and transmission electron microscopy studies. The cation arrangement determines the transition metal-oxygen covalency and structural reversibility related to voltage decay. The identification of structural arrangement with de-lithiated oxygen-centred octahedron and interactions between octahedrons affecting the oxygen stability and transition metal mobility of layered oxide provides the insight into the degradation chemistry of cathode materials and a way to develop high-energy density electrodes.

Effect of Nb5+ charge neutralization substitution on the electrochemical performance of lithium-rich layered oxides

The effect of the Nb5+ substitution with a charge-compensated strategy in lithium-rich layered oxides (LLOs) Li1.2Ni0.13+xCo0.13-xMn0.54-xNbxO2 (x = 0, 0.01, 0.02, and 0.03) has been investigated systematically. A hydroxide co-precipitation method followed by a high-temperature solid-state reaction is adopted in the synthesis process. Structural characterization confirms that the low dose substituting of Nb5+ in the layered structures forms a solid solution, and the samples show low cation mixing and enlarged Li+-diffusing channels, which imply favorable high-rate capability. The initial charge/discharge measurements suggest that the oxygen loss from the network during the delithiation process has been suppressed by the substitution of Nb5+ due to the formation of robust Nb–O bonds and a decrease in TM-O (TMs are transition metals) covalence. Moreover, these Nb–O bonds contribute to the stabilization of the crystalline framework, resulting in an excellent cycle stability with a mitigated voltage decay.

Electrochemical and structural analysis of Mg substitution in lithium-rich layered oxide for lithium-ion battery

Mg-doped lithium-rich layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 with smooth morphology is synthesized by co-precipitation followed by calcination. The morphologies of bare particles and electrodes have been studied through scanning electron microscopy (SEM), which illustrates that, compared with the Mg-doped particles, the pristine particles are characteristic of angular and corrosion is much more likely to happen. Additionally, the Mg substitution can make the crystal structure stable during the electrode process and then enhance the cycle performance. Electrochemical impedance spectroscopy and transmission electron microscopy have been utilized to gain insight to the properties of pristine and Mg-doped particles before and after the electrode process. Mg-doped particles show lower charge transfer resistance and higher diffusion coefficients (D) of the diffusing lithium ions. After 100 cycles at 250 mA g−1, the morphology and crystal structure of Mg-doped materials show smaller changes than those of pristine particles.

Enhancing the electrochemical performance of Li-rich layered oxide Li1.13Ni0.3Mn0.57O2 via WO3 doping and accompanying spontaneous surface phase formation

WO3 doping and accompanying spontaneous formation of a surface phase can substantially improve the discharge capacity, rate capability, and cycling stability of Co-free Li-rich layered oxide Li1.13Ni0.3Mn0.57O2 cathode material. X-ray photoelectron spectroscopy, in conjunction with ion sputtering, shows that W segregates to the particle surfaces, decreases the surface Ni/Mn ratio, and changes the surface valence state. High-resolution transmission electron microscopy further suggests that W segregation increases surface structural disorder. The spontaneous and simultaneous changes in the surface structure, composition, and valence state represent the formation of a surface phase (complexion) as the preferred surface thermodynamic state. Consequently, the averaged discharge capacity is increased by ∼13% from 251 to 284 mAh g−1 at a low rate of C/20 and by ∼200% from 30 to 90 mAh g−1 at a high rate of 40C, in comparison with an undoped specimen processed under identical conditions. Moreover, after 100 cycles at a charge/discharge rate of 1C, the WO3 doped specimen retained a discharge capacity of 188 mAh g−1, being 27% higher than that of the undoped specimen. In a broader context, this work exemplifies an opportunity of utilizing spontaneously-formed surface phases as a scalable and cost-effective method to improve materials properties.

Nanoscale gadolinium doped ceria (GDC) surface modification of Li-rich layered oxide as a high performance cathode material for lithium ion batteries

Nanoscale gadolinium doped ceria (GDC) has been successfully coated on Li-rich layered oxides Li1.2Mn0.54Ni0.13Co0.13O2 by a wet chemical deposition approach. Structure and morphology of the fabricated materials are characterized by XRD, SEM, TEM and XPS. The electrochemical testing results demonstrated that Li1.2Mn0.54Ni0.13Co0.13O2 with 3 wt% GDC coating shows outstanding electrochemical performance in regards of capacity retention and charge transfer resistance. The improved electrochemical performance can be ascribed to that the GDC coating layer can protect the Li1.2Mn0.54Ni0.13Co0.13O2 from being corroded by the organic electrolyte and provide sufficient active sites for electrons and Li+ ions diffusion and transportation. Moreover, the GDC coating layer can effectively suppress the oxygen loss from bulk Li1.2Mn0.54Ni0.13Co0.13O2 in the first charge process due to the oxygen vacancies in GDC, which resulting in an improved initial coulombic efficiency. The nanoscale GDC layer homogenously incorporated into LLMO surface can effectively keep the structure stability and mitigate the voltage fade during cycling.