Li-rich Layered Oxide Li1 Research Articles

Mitigating degradation and modulating electronic structure via an epitaxial perovskite protection for Li-rich layered oxides

Li-rich layered oxides are highly promising cathode materials for the next-generation lithium-ion batteries due to their extraordinary specific capacity and hence high energy density. However, their practical application is hindered by the structural and surface instabilities as well as sluggish reaction kinetics. Herein, a low-crystallinity perovskite oxide (NdTiO3) is developed to epitaxially conform the surface of a typical Li-rich layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 to overcome these drawbacks. Experimental and computational results confirm that this surface phase not only mitigates structural deformation and interfacial side reactions, but also can modulate the electronic structure of Li2MnO3 for the higher electron conductivity. As a result, the epitaxially-protected cathode material displays much better cycle stability (222.02 mA h g−1 after 200 cycles at 1C compared to 185.06 mA h g−1 for the uncoated one) and excellent rate capability (155.71 mA h g−1 at 5C). A pouch-type full cell using commercial graphite anode demonstrates an energy density (381.38 Wh kg−1 based on the cathode and anode) and a capacity retention of 91.1% after 100 cycles.

Correlating Rate-Dependent Transition Metal Dissolution between Structure Degradation in Li-Rich Layered Oxides.

Understanding the mechanism of the rate-dependent electrochemical performance degradation in cathodes is crucial to developing fast charging/discharging cathodes for Li-ion batteries. Here, taking Li-rich layered oxide Li1.2 Ni0.13 Co0.13 Mn0.54 O2 as the model cathode, the mechanisms of performance degradation at low and high rates are comparatively investigated from two aspects, the transition metal (TM) dissolution and the structure change. Quantitative analyses combining spatial-resolved synchrotron X-ray fluorescence (XRF) imaging, synchrotron X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques reveal that low-rate cycling leads to gradient TM dissolution and severe bulk structure degradation within the individual secondary particles, and especially the latter causes lots of microcracks within secondary particles, and becomes the main reason for the fast capacity and voltage decay. In contrast, high-rate cycling leads to more TM dissolution than low-rate cycling, which concentrates at the particle surface and directly induces the more severe surface structure degradation to the electrochemically inactive rock-salt phase, eventually causing a faster capacity and voltage decay than low-rate cycling. These findings highlight the protection of the surface structure for developing fast charging/discharging cathodes for Li-ion batteries.

Oxygen-defects evolution to stimulate continuous capacity increase in Co-free Li-rich layered oxides

Though oxygen defects are associated with deteriorated structures and aggravated cycling performance in traditional layered cathodes, the role of oxygen defects is still ambiguous in Li-rich layered oxides due to the involvement of oxygen redox. Herein, a Co-free Li-rich layered oxide Li1.286Ni0.071Mn0.643O2 has been prepared by a co-precipitation method to systematically investigate the undefined effects of the oxygen defects. A significant O2 release and the propagation of oxygen vacancies were detected by operando differential electrochemical mass spectroscopy (DEMS) and electron energy loss spectroscopy (EELS), respectively. Scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) reveals the oxygen vacancies fusing to nanovoids and monitors a stepwise electrochemical activation process of the large Li2MnO3 domain upon cycling. Combined with the quantitative analysis conducted by the energy dispersive spectrometer (EDS), existed nano-scale oxygen defects actually expose more surface to the electrolyte for facilitating the electrochemical activation and subsequently increasing available capacity. Overall, this work persuasively elucidates the function of oxygen defects on oxygen redox in Co-free Li-rich layered oxides.

High-voltage all-solid-state lithium metal batteries prepared by aerosol deposition

High-energy-density and safe rechargeable batteries are key components to realizing a low-carbon society. All-solid-state Li-metal batteries have the potential to achieve both high safety and high energy densities. However, the large interfacial resistance between solid electrolytes and cathodes is the major challenge for developing all-solid-state Li-metal batteries. Here we deposited a Li-rich layered metal oxide Li1.2Mn0.54Ni0.13Co0.13O2 (LMNC) thin film (6 µm thick) on an Al-doped Li7La3Zr2O12 (LLZO) substrate at room temperature by aerosol deposition. The LMNC particles were coated with Li3BO3 (LBO), which acted as a binder to hold LMNC and LLZO together at heating. As a result, good interfacial contact was achieved between LMNC and LLZO. Yet reactions between LMNC and LBO would occur at heat treatment temperatures above 600 °C. The highest discharge capacity of the all-solid-state Li/LLZO/LBO-LMNC cell at 0.1 C and 60 °C was 223 mAh g-1. The main reason for the cell capacity decay was the cracking of the LBO-LMNC cathode layer during cycling. Searching for a more suitable binder material with a high fracture toughness is crucial for further developing the aerosol-deposited LLZO-based all-solid-state Li metal batteries.

Improvement of stability and capacity of Co-free, Li-rich layered oxide Li1.2Ni0.2Mn0.6O2 cathode material through defect control

Layered oxides based on manganese (Mn), rich in lithium (Li), and free of cobalt (Co) are the most promising cathode candidates used for lithium-ion batteries due to their high capacity, high voltage and low cost. These types of material can be written as xLi2MnO3·(1 − x) LiTMO2 (TM = Ni,Mn,etc.). Though, Li2MnO3 is known to have poor cycling stability and low capacity, which hinder its industrial application commercially. In this work, Li1.2Ni0.2Mn0.6O2 materials with different amounts of structural defects was successfully synthesized using powder metallurgy followed by different cooling processes in order to improve its electrochemical properties. Microstructural analyses and electrochemical measurements were carried out on the study samples synthesized by a combination of X-ray diffraction, transmission electron microscopy, and cyclic voltammetry. It is found that the disorder of the transition metal layer in Li2MnO3 promotes its electrochemical activity, whereas the Li/Ni antisites of the Li layer maintain the stability of its local structure. The material with optimal amount of structural defects had an initial capacity of 188.2 mAh g−1, while maintaining an excellent specific capacity of 144.2 mAh g−1 after 500 cycles at 1C. In comparison, Li1.2Ni0.2Mn0.6O2 without structural defect only gives a capacity of 40.8 mAh g−1 after cycling. This microstructural control strategy provides a simple and effective route to develop high-performance Co-free, Li-rich Mn-based cathode materials and scale-up manufacturing.

Charge Compensation Mechanism and Structural Change of Li-Rich Layered Oxide Li1.23Mn0.46Fe0.15Ni0.15O2 Electrode during Charging and Discharging

We investigated changes in the valence and structure of positive electrodes composed of Li-rich layered manganese (Mn) oxides (Li1.23Mn0.46Fe0.15Ni0.15O2, LMFN) when they were charged and discharged. Hard X-ray photoemission spectroscopy (HAXPES) and 57Fe Mössbauer spectroscopy measurements indicated that charge compensation occurred through changes in the valences of the Mn, Fe, Ni, and oxide ions, from Mn4+, Fe3.2+, Ni3.4+, and O1.78− in the charged state to Mn3.6+, Fe3+, Ni2+, and O2− in the discharged state. Neutron diffraction (ND) measurements indicated the LMFN powder had a layered rock-salt structure. However, reconstruction of the transition metal and oxide ions in the lattice during charging indicated spinel phases made up 17% of the structure, the remaining 83% being layered rock-salt. The oxygen deficiency formed during charging recovered during discharging and the lost oxygen became implanted again in the lattice of the cathode. We believe that the elucidation of the charge compensation mechanism and structural changes during charging and discharging will be useful for designing materials with larger capacity and improved cycle performance.

Improved electrochemical activity of the Li2MnO3-like superstructure in high-nickel Li-rich layered oxide Li1.2Ni0.4Mn0.4O2 and its enhanced performances via tungsten doping

Voltage decay of Li- and Mn-rich layered oxides can be effectively suppressed by increasing their Ni contents, which however normally results in a sizable decrease in capacity probably due to the reduced Li2MnO3-like superlattice component. Here, we reveal that the partial replacement of Mn by W in the high-nickel Li-rich (HNLR) layered oxide Li1.2Ni0.4Mn0.4O2 leads to the increase in both Li2MnO3-like superlattice component and Ni2+ proportion due to the presence of W6+. As a result, the doping of W favors the activation of the Li2MnO3-like component with the reversible redox of more oxygen anions and the creation of a multi-cation chemical environment, accompanied by the size reduction of primary particles and the increase in lattice parameters. The reversible redox of more oxygen anions results in much higher capacity and initial Coulombic efficiency. The reduced sizes of primary particles, along with the lattice expansion significantly enhance the electrochemical kinetics, which accounts for superior rate capability and excellent high-rate cycling performance. This study opens a possibility of improving the performance of HNLR oxides by doping appropriate elements to modify and optimize the properties of the Li2MnO3-like component.

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.

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.

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.

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 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.

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.

Enhanced electrochemical performance of Li-rich layered cathode materials via chemical activation of Li2MnO3 component and formation of spinel/carbon coating layer

Li-rich layered oxides are promising cathode materials for advanced Li-ion batteries because of their high specific capacity and operating potential. In this work, the Li-rich layered oxide Li1·2Mn0·54Ni0·13Co0·13O2 (LMNC), is modified via a carbonization-reduction process (yielding the corresponding reduced compound denoted LMNC-R). Compared to the pristine oxide, LMNC-R delivers significantly enhanced initial discharge capacity/columbic efficiency, remarkably improved rate performance with an accelerated Li+ diffusion rate, and significantly increased capacity/voltage retention. The specific energy density and energy retention after 100 cycles increase from 378.2 Wh kg−1 and 47.7% for LMNC to 572.0 Wh kg−1 and 71.3%, respectively, for LMNC-R. The enhancement in the electrochemical performance of LMNC-R can be attributed to the synchronous formation of the oxygen non-stoichiometric Li2MnO3-δ component and to the carbon/spinel double coating layer in the material that resulted from the post-treatment process. Thus, the carbonization-reduction modification process can be used to tailor the structural evolution procedure and to suppress the metal ion dissolution of the Li-rich layered oxide during cycling.

Li1.2Ni0.13Co0.13Mn0.54O2 with Controllable Morphology and Size for High Performance Lithium-Ion Batteries.

The controllable morphology and size Li-rich Mn-based layered oxide Li1.2Ni0.13Co0.13Mn0.54O2 with micro/nano structure is successfully prepared through a simple coprecipitation route followed by subsequent annealing treatment process. By rationally regulating and controlling the volume ratio of ethylene glycol (EG) in hydroalcoholic solution, the morphology and size of the final products can be reasonably designed and tailored from rod-like to olive-like, and further evolved into shuttle-like with the assistance of surfactant. Further, the structures and electrochemical properties of the Li-rich layered oxide with various morphology and size are systematically investigated. The galvanostatic testing demonstrates that the electrochemical performances of lithium ion batteries (LIBs) are highly dependent on the morphology and size of Li1.2Ni0.13Co0.13Mn0.54O2 cathode materials. In particular, the olive-like morphology cathode material with suitable size exhibits much better electrochemical performances compared with the other two cathode materials in terms of initial reversible capacity (297.0 mAh g-1) and cycle performance (95.4% capacity retention after 100 cycles at 0.5 C), as well as rate capacity (142.8 mAh g-1 at 10 C). The excellent electrochemical performances of the as-prepared materials could be related to the synergistic effect of well-regulated morphology and appropriate size as well as their micro/nano structure.

Tailoring the (Ni 1/6 Co 1/6 Mn 4/6 )CO 3 precursors of Li-rich layered oxides for advanced lithium-ion batteries with the seed-mediated method

Abstract To enhance the energy density of Li-rich layered oxide Li1.2(Ni0.133Co0.133Mn0.533)O2 (LNCMO), the seed-mediated method is explored to prepare the (Ni1/6Co1/6Mn4/6)CO3 precursors. The nucleation and growth of the spherical precursors are successfully separated and controlled with the seed-mediated method in the co-precipitation process. Therefore, the particle size distribution and then the tap density of the precursors can be tailored by the seed-mediated method. To further manipulate the properties of the carbonate precursors, (Ni1/6Co1/6Mn4/6)CO3 is prepared by the seed-mediated method at different pH values. The influences of the feeding ways and pH values in the co-precipitation process on the morphologies, particle size distributions and tap densities of the precursors are investigated. As a result, the (Ni1/6Co1/6Mn4/6)CO3 precursor with a high tap density and moderate particle size distribution is obtained. After lithiated, the LNCMO samples deliver high discharge capacities, high volumetric energy densities and stable cycle stabilities. The main reasons for these improvement are preliminarily discussed in this paper.

Lithium-Rich Layered Oxide Li1.18 Ni0.15 Co0.15 Mn0.52 O2 as the Cathode Material for Hybrid Sodium-Ion Batteries.

Li-rich layered oxide Li1.18 Ni0.15 Co0.15 Mn0.52 O2 (LNCM) is, for the first time, examined as the positive electrode for hybrid sodium-ion battery and its Na(+) storage properties are comprehensively studied in terms of galvanostatic charge-discharge curves, cyclic voltammetry and rate capability. LNCM in the proposed sodium-ion battery demonstrates good rate capability whose discharge capacity reaches about 90 mA h g(-1) at 10 C rate and excellent cycle stability with specific capacity of about 105 mA h g(-1) for 200 cycles at 5 C rate. Moreover, ex situ ICP-OES suggests interesting mixed-ions migration processes: In the initial two cycles, only Li(+) can intercalate into the LNCM cathode, whereas both Li(+) and Na(+) work together as the electrochemical cycles increase. Also the structural evolution of LNCM is examined in terms of ex situ XRD pattern at the end of various charge-discharge scans. The strong insight obtained from this study could be beneficial to the design of new layered cathode materials for future rechargeable sodium-ion batteries.