Hexagonal Layered Structure Research Articles

Layered Li1+x(Ni0.33Co0.33Mn0.33)O2 cathode material prepared by microwave assisted solvothermal method for lithium ion batteries

Layered hexagonal structure Li1+x(Ni0.33Co0.33Mn0.33)O2 (LNCM) (x=0, 0.05, 0.1, 0.15 and 0.2mol%) compounds were prepared by microwave assisted solvothermal method at two different calcination temperature of 850 and 950°C. The phase purity of the LNCM compounds was confirmed by Rietveld refined XRD pattern, Raman, and HRTEM studies. The average particle sizes were in the submicron range as confirmed by SEM and TEM analysis. Galvanostatic cycling studies were made in various voltage range, 2.5 to 4.4/4.6/4.8V at a current rate of 0.2C. Among all the compounds, LNCM prepared at 950°C (HS3) exhibited an initial discharge capacity of 197mAh/g and maintained a capacity of 180mAh/g at the end of 40th cycle in 2.5–4.6V window, indicating an excellent capacity retention. HS3 shows the electrical conductivity of 9.31×10−6S/cm, which was higher than all the other compounds and discussed the reason for the improved electrochemical performance.

Comparison of Ag(In,Ga)Se2/Mo and Cu(In,Ga)Se2/Mo Interfaces in Solar Cells.

The structural and electrical properties of the junction at Ag(In,Ga)Se2AIGS/Mo, and Cu(In,Ga)Se2 CIGS/Mo layers were characterized. The region between the CIGS and Mo featured a MoSe2 layer with a layered hexagonal structure and thickness of 10-15 nm. The c-axis of the MoSe2 was oriented perpendicular to the Mo layer, and the c -value was 12.6 Å. However, no such layer was observed at the interface between AIGS and Mo. This result was also confirmed by energy-dispersive X-ray spectrometry and X-ray diffraction measurements of the MoSe2 layer. The CIGS/Mo with a MoSe2 layer formed an ohmic contact, while the AIGS/Mo without the MoSe2 layer formed a Schottky contact. This Schottky contact showed a barrier height of 0.8 ± 0.02 eV, a nonideality factor of 1.5 ± 0.1, and a series resistance of 370 ± 8 Ω. A schematic band diagram of the AIGS/Mo junction was constructed on the basis of the above results.

A facile method for synthesis of LiNi0.8Co0.15Al0.05O2 cathode material

Well-ordered layered structure LiNi0.8Co0.15Al0.05O2 cathode material is successfully synthesized by two-step method. This synthesis method is based on the formation of ternary oxide precursors by calcining the nickel-cobalt-aluminum composite oxalates, followed by subsequent lithiation under different synthesis temperatures. TG/DSC analysis is applied to investigate the reaction synthesis processed of composite oxalates and the lithiation of ternary oxide precursors. The effects of sintering temperature on crystal structure, particles morphology and electrochemical features are evaluated through XRD, SEM, CV, EIS and charge/discharge studies. The sample prepared at an optimal temperature of 750°C has the best-ordered hexagonal layer structure and exhibits best electrochemical performance with an initial discharge capacity of 199.9mAhg−1 at 0.2C. Both samples sintered at 700°C and 750°C display a good cyclic stability, the capacity retention at 1C after 60cycles is 94.2% and 92.0%, respectively.

LiNi0.8Co0.15Al0.05O2: Enhanced Electrochemical Performance From Reduced Cationic Disordering in Li Slab

Sub-micron sized LiNi0.8Co0.15Al0.05O2 cathode materials with improved electrochemical performance caused by the reduced cationic disordering in Li slab were synthesized through a solid state reaction routine. In a typical process, spherical precursor powder was prepared by spray drying of a uniform suspension obtained from the ball-milling of the mixture of the starting raw materials. Then the precursor powders were pressed into tablets under different pressures and crushed into powder. The pressing treated powders were finally calcinated under oxygen atmosphere to obtain the target cathode materials. XRD investigation revealed a hexagonal layered structure without impurity phase for all samples and significant increase in the diffraction intensity ratio of I(003)/I(104) was observed. Rietveld refinement further confirmed the reduced cationic disordering in Li slab by such pressing treatment, and the smallest disordering was observed for sample S4 with only 1.3% Ni ions on Li lattice position. The electrochemical testing showed an improvement in electrochemical behavior for those pressing treated samples. The calculation of diffusion coefficients using EIS data showed improved Li diffusion coefficient after pressing treatment. The sample S4 presented a diffusion coefficient of 4.36 × 10−11 cm2·s−1, which is almost 3.5 times the value of untreated sample.

Comparative Studies of Ti Doped LiNi0.7Co0.3O2 and LiNi0.7Co0.3O2 Nano Cathode Material for High Energy Density Li-Ion Battery

Ti doped LiNi0.7Co0.3O2 materials were investigated for their electrochemical characteristics. LiNi0.7Co0.3O2 and LiNi0.6Co0.3Ti0.1O2 materials were prepared using a self-propagating combustion method. The structure and morphology of the materials were characterized using X-Ray Diiffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-Ray Spectroscopy (EDX). The oxidation state of elements and their chemical environments were studied using X-Ray Photoelectron Spectroscopy (XPS). XRD results showed that the materials were all single phase with hexagonal layered structure of R-3m space group. The discharge capacities are between 135.5 and 151.1 mAhg-1. The LiNi0.7Co0.3O2 compound exhibits the highest first cycle capacity of 151.1 mAhg-1 over the voltage range of 2.5 to 4.2 V compared to the Ti doped sample LiNi0.6Co0.3Ti0.1O2, showing a capacity of 146 mAhg-1. However, at the 30th cycle, the Ti doped material shows the highest specific discharge capacity of 137.8 mAhg-1. The capacity fading is only about 5.6 % compared to 38.2% for undoped LiNi0.7Co0.3O2. Therefore, eventhough the undoped LiNi0.7Co0.3O2 material has a higher first cycle capacity, the doped compounds exhibits much better capacity retention over 30 cycles

Specific Capacity and Capacity Fading of Interstitial and Substitutional Doping of Li in LiNi0.6Co0.3Ti0.1O2 Nano Cathode Material for High Energy Density Li-Ion Battery

Pure and single phase LiNi0.6Co0.3Ti0.1O2, Li1.05Ni0.6Co0.3Ti0.1O2, Li1.05Ni0.55Co0.3Ti0.1O2 materials were successfully prepared using a self-propagating combustion method. The structure and morphology of the materials were characterized using X-Ray Diiffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-Ray Spectroscopy (EDX). The oxidation state of elements and their chemical environments were studied using X-Ray Photoelectron Spectroscopy (XPS). The electrochemical performances of the materials were carried by means of galvanostatic charge-discharge on the fabricated cells. XRD results showed that the materials are impurity-free and single phase with well ordered hexagonal layered structure of R-3m space group. The discharge capacities are between 141 and 145 mAhg-1. The interstitially doped Li1.05Ni0.6Co0.3Ti0.1O2 compound exhibits the highest first cycle capacity of 145.3 mAhg-1 over the voltage range of 2.5 to 4.2 V compared to the undoped sample, LiNi0.6Co0.3Ti0.1O2, showing a capacity of 105.5 mAhg-1. The 70th cycle revealed that the Li interstitially doped material (Li1.05Ni0.6Co0.3Ti0.1O2) shows the highest specific discharge capacity of 132.4 mAhg-1. The capacity fading is only about 8.9% compared to 25.4% for undoped LiNi0.6Co0.3Ti0.1O2 and 10.4% for Li substitutionally doped material (Li1.05Ni0.55Co0.3Ti0.1O2). XPS studies showed that the binding energy of Li 1s is lowest for the best performance compound meaning that the Li+ ions can be extracted more easily from Li1.05Ni0.6Co0.3Ti0.1O2 than the other two materials supporting the electrochemical behaviour of the materials.

Recycling of LiCo0.59Mn0.26Ni0.15O2 cathodic material from spent Li-ion batteries by the method of the citrate gel combustion

The Li-ion batteries are the main power source for the high technology devices, such as mobile phones and electric vehicles. Because of that, the number of spent Li-ion batteries significantly increases. Today, the number of active mobile phones crossed 7.19 billion. It is estimated that the mass of the spent lithium ion batteries in China will exceed 500,000 t by 2020. The trouble is in the ingredients of these batteries. They contain Li, Co, Mn, Ni, Cu, Al and toxic and flammable electrolytes which have a harmful affection to the environment. Because of that, the recycling procedure attracts raising attention of researches. Several commercial spent Li-ion batteries were recycled by the relatively fast, economic and simple procedure. The three ways of separating the cathode material from Al collector were examined after the manual dismantling of the components of batteries with the Li(Co?Mn?Ni)O2 as cathode material. These were: 1. dissolution of the Al collector in the alkali medium, 2. peeling off with N-methylpyrrolidone and 3. thermal decomposition of the adhesive at 700?C. The procedure with the highest yield was the one with the dissolution in alkali medium. The chemical analysis of the single batteries'' components (the crust, Al/Cu collector, cathode material) were done by the atomic absorption spectrometry. The components, before the analysis, were dissolved. The re-synthesis of the cathode material by the method of the citrate gel combustion was done after the separating the cathode material and dissolving it in the nitric acid. The obtained product was, after annealing, characterized by the methods of X-ray diffraction and Raman spectroscopy. The recycled product was LiCo0.59Mn0.26Ni0.15O2 stoichiometry, with the hexagonal layered structure ?-NaFeO2 type. The functionalization of the resynthesized material was examined in the 1 M solution LiClO4 in the propylene carbonate, by galvanostatic charging, with the current density of 0.7C. The recycled material showed relatively good capacities of charging and discharging which are 94.9 i 64.8 mA h g?1, respectively.

Pressure induced topological phase transition in layered Bi2S3.

A large bulk band gap and tunable Dirac carriers are desired for practical device applications of topological insulators. However, most known topological insulators are narrow gap materials and the manipulation of their Dirac surface states is limited by residual bulk charge carriers originating from intrinsic defects. In this study, via density functional theory based first-principles calculations, we predict that a layered hexagonal structure of Bi2S3 is stable, and it becomes a topological insulator under a moderate compressive pressure of about 5.3 GPa. Interestingly, we find that the strength of the spin-orbit interaction in Bi2S3 can be effectively enhanced by the applied pressure. This leads to an increased inverted band gap with pressure, which can reach 0.4 eV with a pressure of 13.7 GPa. Compared to Bi2Se3, intrinsic defects are suppressed in Bi2S3 under both cation- and anion-poor growth conditions. Our calculations predict a new Bi-based topological insulator, and also shed light on control over spin-orbit interactions in Bi2S3 and tuning of its topological properties.

Study on the reversible capacity loss of layered oxide cathode during low-temperature operation

Abstract In this study, commercial Li(Ni1/3Co1/3Mn1/3)O2/graphite (NCM/C) lithium-ion batteries were cycled at −10 °C under different current rates ranging from 0.2 C to 1C. Electrochemical measurements and post-mortem analysis were performed to identify the root causes of the degradation in the electrochemical performance of the cells. The results reveal that apart from the increase of lithium plating on the anode, there is a considerable and abnormal capacity loss on the NCM cathode with the increase in current rate. The different degradation mechanisms including the loss of lithium inventory (LLI) and the specific capacity loss of NCM material (LAM) during cycling at −10 °C were analyzed quantitatively. It is shown that the evolution trend of LLI with the increase in current rate (8.6%, 35.0%, 55.8% for 0.2 C, 0.5 C and 1 C respectively) corresponds closely to that of the capacity loss of the full-cells (8.6%, 45.5%, 63.6% for 0.2 C, 0.5 C and 1 C, respectively), which is different to the trend of LAM (7.2%, 8.8%, 22.3% for 0.2 C, 0.5 C and 1 C, respectively). Further analysis by XRD and HR-TEM clearly indicates that the crystallinity of the hexagonal layered structure of NCM was greatly impaired after low-temperature cycling at −10 °C, and spinel phase can be observed among the layered structure.

Rapid preparation of nano hexagonal-shaped hydrocalumite via one-pot mechanochemistry method

Hexagonal-shaped hydrocalumite (Ca–Al layered double hydroxides) was successfully synthesized by one-step mechanochemistry method within only 30min. The product was characterized by X-ray diffraction, Fourier Transform Infrared spectroscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, elemental mapping analysis, transmission electron microscopy, X-ray fluorescence, and thermogravimetric analysis. The results showed that the formation of a well-defined hydrocalumite and the microstructural evolution were strongly dependent on the milling time. From XRD profiles, a well-crystallized hydrocalumite with higher peaks intensity was formed after 60min of milling, while the sharpness and intensity of LDH-derived XRD peaks decreased as milling time increased. Microscopic analysis showed that the product had hexagonal layered structure with lateral dimension of 100 to 200nm. In addition, the thermal decomposition of the product is reported in details. This study offers a low-cost approach to synthesis of hydrocalumite owing to simplicity and extremely short processing time.

High-pressure X-ray diffraction, Raman, and computational studies of MgCl2 up to 1 Mbar: Extensive pressure stability of the β-MgCl2 layered structure.

Magnesium chloride (MgCl2) with the rhombohedral layered CdCl2-type structure (α-MgCl2) has been studied experimentally using synchrotron angle-dispersive powder x-ray diffraction and Raman spectroscopy using a diamond-anvil cell up to 100 GPa at room temperature and theoretically using first-principles density functional calculations. The results reveal a pressure-induced second-order structural phase transition to a hexagonal layered CdI2-type structure (β-MgCl2) at 0.7 GPa: the stacking sequence of the Cl anions are altered resulting in a reduction of the c-axis length. Theoretical calculations confirm this phase transition sequence and the calculated transition pressure is in excellent agreement with the experiment. Lattice dynamics calculations also reproduce the experimental Raman spectra measured for the ambient and high-pressure phase. According to our experimental results MgCl2 remains in a 2D layered phase up to 100 GPa and further, the 6-fold coordination of Mg cations is retained. Theoretical calculations of relative enthalpy suggest that this extensive pressure stability is due to a low enthalpy of the layered structure ruling out kinetic barrier effects. This observation is unusual, as it contradicts with the general structural behavior of highly compressed AB2 compounds.

Self-Assembly of n-Shaped Rod–Coil Molecules into Thermoresponsive Nanoassemblies: Construction of Reversible Helical Nanofibers in Aqueous Environment

Amphiphilic coil–rod–coil molecules 1–3, consisting of an n-shaped rod building block and poly(ethylene oxide) (PEO) with a degree of polymerization of 5 linked through a biphenyl unit as the coil segment, were synthesized. Molecule 1 self-assembles into lamellar and hexagonal perforated layer structures, in the crystalline and liquid crystalline phases, respectively. Remarkably, molecule 2 incorporating lateral methyl groups between the rod and coil segments spontaneously self-organizes into hexagonal perforated layer and oblique columnar structures. The additional incorporation of a lateral butyl group at the center of the rod segment of molecule 2 generates molecule 3, which assumes an exclusively oblique columnar structure in the solid state. In aqueous solutions, molecule 1 self-assembles into fibrous aggregates, whereas molecules 2 and 3 exhibit a self-organizing capacity to form helical fibers. Additionally, circular dichroism (CD) experiments and atomic force microscope (AFM) measurements of molec...

Synthesis, structural and electrical properties of Li1.2Mn0.54Ni0.13Co0.13O2 synthesised by sol–gel method

In this present study, we have reported the synthesis of Li-rich Li1.2Mn0.54Ni0.13Co0.13O2 by sol–gel method which is used as cathode material in Li-ion batteries (LIBs). X-ray diffraction confirms the crystallisation of synthesised material in the hexagonal layered structure of space group R-3 m. Fourier transform infrared spectroscopy confirmed the functional groups. Field-emission scanning electron microscopy equipped with X-ray spectrometer attributed to the morphology and elemental composition of the material. Electric and dielectric properties were investigated in the frequency range of 50 Hz–5 MHz for the temperatures ranging from 313 to 773 K. Conduction mechanism of the cathode material in LIBs was investigated for the grain and grain boundaries in the material. Electric properties of the material were investigated in the framework of impedance, electric modulus and conductivity. Nyquist plot showed the non-Debye nature of the material. The important parameters such as Maxwell–Wagner relaxation, hopping mechanism, activation energy, ionic mobility in the material are investigated. The interfacial ion transport mechanism of conductivity is studied using Jonscher’s Power Law.

In Situ XRD Studty on Phase Transitions of NaNi1/3Fe1/3Mn1/3O2 Cathode Materials

Sodium is one of the more abundant elements on earth and exhibits similar chemical properties to lithium, which indicating that sodium-based batteries could provide an alternative chemistry to lithium batteries particularly in large scale energy storage. Furthermore, for positive electrode materials sodium intercalation chemistry is very similar to Li, and the electrochemical equivalent and standard potential of sodium, all of these are the most advantageous for sodium ion battery quickly develop and apply to commercialization. In this paper, the NaNi1/3Fe1/3Mn1/3O2 material was prepared using a large-scale synthesis process and its electrochemical characteristics were measured. In situ synchrotron XRD have been applied to identify phase transformation of NaNi1/3Fe1/3Mn1/3O2 materials during the sodium ions deintercalation. The morphology, crystal structure and electrochemical characteristics of the prepared NaNi1/3Fe1/3Mn1/3O2 were mesured. It can be found, the sample shows a typical spherical particle size of about 5 μm and composed of many dense and plate-like primary particles. The XRD pattern of the pristine sample confirms the O3-type NaNi1/3Fe1/3Mn1/3O2 could be successfully modeled as the hexagonal layered structure which can be indexed to R-3m space-group with the α-NaFeO2 structure, and the lattice parameters are a = b = 2.9684 Å and c =16.128 Å. The oxygen stacking is ABC and the closest packing arrangement is hexagonally closest-packed. The charge-discharge capacities of NaNi1/3Fe1/3Mn1/3O2 were 131.5 mAh g-1 and 134.7 mAh g-1 in the first cycle, and maintained at 135.3 mAh g-1 and 135.1 mAh g-1 after 10 cycles at 0.1 C rate, and the first cycle charge-discharge capacity reached at 122.3 mAh g-1 and 122.1 mAh g-1at 1C rate, respectively.In order to understand the metastable structure and phase transformation of NaNi1/3Fe1/3Mn1/3O2 materials during Na ion intercalation, we performed in situ synchrotron XRD on a NaNi1/3Fe1/3Mn1/3O2/C battery during charging process. In situ synchrotron x-ray powder diffraction measurements were carried out in transmission geometry at beamline 17-BM of the Advanced Photon Source at Argonne National Laboratory (wavelength 0.7270 Å, 500-mm-diameter beam).The synchrotron in-situ XRD results demonstrate the phase transformations in nanoparticulate NaNi1/3Fe1/3Mn1/3O2 proceed via a continuous change in structure during cycling, The structure changed from O3-type NaNi1/3Fe1/3Mn1/3O2 to hexagonal P3 type Na1- dNi1/3Fe1/3Mn1/3O2 via two layer hexagonal structures coexists with a monoclinic O’3 and P’3. ACKNOWLEDGMENT This work was supported by the Natural Science Foundation of China (21336003, 21573147 and 21506123), the 973 Program of China (2014CB239703), the US Department of Energy under contract DE-AC02-06CH11357 from the Vehicle Technologies Office, Department of Energy, Office of Energy Efficiency and Renewable Energy, and the Science and Technology Commission of Shanghai (14DZ2250800). References (1) Nagelberg A. S.; Worrell W. L. J. Solid State Chem.,1979, 29, 345–354. (2) Pan H.; Hu Y.S.; Chen L. Energy Environ. Sci., 2013, 6, 2338. (3) Komaba S.; Yabuuchi N.; Nakayama T.; Ogata A.; Toru Ishikawa T.; Nakai I. Inorg. Chem.2012, 51, 6211−6220. (4) Delmas, C.; Braconnier, J.-J.; Fouassier, C.; Hagenmuller, P. Solid State Ionics .1981, 3-4, 165–169. (5) Berthelot, R., Carlier, D. & Delmas, C. Nat. Mater. 2011, 10, 74–80. (6) Y. L. Cao, L. F. Xiao, W. Wang, D. W. Choi, Z. M. Nie, J. G. Yu, L. V. Saraf, Z. G. Yang and J. Liu, Adv. Mater. 2011, 23, 3155–3160. (7) Wang H; Liao X.Z.; Yang Y.;Yan X.;He Y.S; Ma Z.F. J . Electrochem . Soc. 2016, 163, A565-A570. (8) Wang H; Liao X.Z.; Xie Y.Y.; Wang M.; Zhou G.; Yang K.; Kang S.; Zhao Z.; Ma Z.F. Energy Storage Sci. Tech. 2016, 5, 65-68

Large-scale ordering of nanoparticles using viscoelastic shear processing.

Despite the availability of elaborate varieties of nanoparticles, their assembly into regular superstructures and photonic materials remains challenging. Here we show how flexible films of stacked polymer nanoparticles can be directly assembled in a roll-to-roll process using a bending-induced oscillatory shear technique. For sub-micron spherical nanoparticles, this gives elastomeric photonic crystals termed polymer opals showing extremely strong tunable structural colour. With oscillatory strain amplitudes of 300%, crystallization initiates at the wall and develops quickly across the bulk within only five oscillations. The resulting structure of random hexagonal close-packed layers is improved by shearing bidirectionally, alternating between two in-plane directions. Our theoretical framework indicates how the reduction in shear viscosity with increasing order of each layer accounts for these results, even when diffusion is totally absent. This general principle of shear ordering in viscoelastic media opens the way to manufacturable photonic materials, and forms a generic tool for ordering nanoparticles.

Experimental investigation of heat transfer enhancement and viscosity change of hBN nanofluids

Hexagonal boron nitride (hBN) is a highly stable dielectric ceramic material that exhibits versatile properties such as, exceptionally high thermal conductivity and good chemical inertness. Due to its layered hexagonal crystal structure, hBN is the softest form among the other polymorphs of BN. Preparation, stability and thermophysical properties of hBN containing DI water, ethylene glycol (EG) and EG–DI water mixture (by volume 50%) based nanofluids are investigated. For this purpose a series of well dispersed, stable nanofluids, containing hBN nanoparticles with a mean diameter of 70nm, are produced with a two-step method, relying on ultrasonication and use of surface active materials such as sodium dodecyl sulfate (SDS) and polyvinyl pyrrolidone (PVP). The effect of these surfactants on the base fluids’ thermophysical properties is measured. The stability is evaluated by quantitative methods such as, time dependent zeta potential, and thermal conductivity measurements. Morphological characterization of nanofluids is completed by qualitative methods such as, SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy). The thermal conductivity enhancement of nanofluids, with particle volume concentration varying between 0.03% and 3%, is investigated experimentally in accordance with their increase in viscosity. It is observed that the hBN nanofluids have remarkably higher thermal conductivity values than their corresponding base fluids, depending on the volume concentration of dispersed nanoparticles. Moreover, water based hBN nanofluids with relatively dilute particle suspensions, exhibits significant increase in thermal conductivity with respect to the viscosity increase.

Infrared-assisted Synthesis of Lithium Nickel Cobalt Alumina Oxide Powders as Electrode Material for Lithium-ion Batteries

This study explores an efficient infrared (IR) heating technique to synthesize highly-crystalline LiNi0.8Co0.15Al0.05O2 (NCA) cathode materials for Li-ion batteries. One home-made IR induction reactor, equipped with medium-wave IR emitter array, is adopted to prepare the NCA powders at 700°C for a calcination period of 1–5h. Two kinds of preparation routes, ball milling and rheological-phase method, are used to prepare NCA precursors. The as-prepared NCA powders display well ordering of hexagonal two-dimensional layer structure with low degree of cation mixing under appropriate conditions: IR heating time (5h) and rheological-phase method. The NCA cathode exhibits an improved discharge capacity, fast Li+ diffusion rate, high rate capability, and good cycling stability. This improved performance mainly originates from low cation mixing, low defect level, and homogeneous particle size of NCA crystals. The carbon-coated NCA cathode offers high capacities of ca. 213 and 115mAhg−1 at 0.1 and 5C, respectively. Analyzed by the Randles-Sevcik plots, the diffusion coefficients in the NCA cathodes increase up to 1.73×10−8 and 5.82×10−9cm2s−1 for Li-extraction and Li-insertion, respectively. Accordingly, the IR heating route turns on a commercial feasibility to synthesize NCA cathode materials for Li-ion battery application.

Li-ion storage performance and electrochemically induced phase evolution of layer-structured Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode material

Li-rich Li[Li0.2Mn0.54Ni0.13Co0.13]O2 (LMNC) powders were synthesized by a gel-combustion method. The related microstructure, electrochemical performance and electrochemically induced phase evolution were characterized. The 900°C calcined powders have a hexagonal layered structure with high ordered degree and low cationic mixing level. The calcined materials as cathode electrode for Li-ion battery deliver the high electrochemical properties with an initial discharge capacity of 243.5 mA•h•g–1 at 25 mA•g–1 and 249.2 mA•h•g–1 even after 50 cycles. The electrochemically induced phase evolution investigated by a transmission electron microscopy indicates that Li+ ions deintercalated first from the LiMO2 (M = Mn, Co, Ni) component and then from Li2MnO3 component in the LMNC during the charge process, while Li+ ions intercalated into Li1–xMO2 component followed by into MnO2 component during the discharge process.

The structure transformation and electrochemical mechanism of cathode material Li0.86V0.8O2

Li0.86V0.8O2 cathode materials were prepared by a simple hydrothermal route. The results showed the as-obtained product had a layered hexagonal structure with the Li/V site disorder. The electrochemical tests in the rechargeable lithium batteries presented a capacity fading during the cycling. The crystal structure and local structure of the material during the cycles were also studied by X-ray diffraction and infrared spectrum, which demonstrated the capacity fading during the electrochemical cycling could be attributed to small irreversible structure change in the first charging process, and the loss of the first discharge can be assigned to the short-range disorder of V ions in the oxygen layers.

Structures, Electrochemical Properties, and Phase Evolution Behaviors of LiNi1-xMnxO2-δ (0 ≤ x ≤ 1/2) as Cathode Materials for Secondary Lithium Batteries

In an attempt to get Co-free layered materials for cathode of secondary lithium batteries, LiNi1-xMnxO2-δ (0 ≤ x ≤ 1/2) samples were synthesized by co-precipitation reactions followed by heating in an O2 atmosphere. The optimum heating temperature to get a single-phase hexagonal layered structure increased with Mn contents in the compound. Oxygen vacancies could be gradually reduced with Mn-substitutions. While the lattice constants, M-O distance, and MO2 slab thickness increased with Mn contents, Li-O and inter-slab distances decreased. Electrical conductivities decreased with Mn contents because of the decreased carrier mobility that resulted from smaller primary particle sizes as well as lager amounts of cation mixing. Samples of x = 1/12 and 1/9 in LiNi1-xMnxO2-δ exhibited 0.1 C-rate discharge capacities of 216.2 and 208.9 mAh g−1 and first cycle efficiencies of 93.3 and 94.0%, respectively. The sample of x = 1/9 in LiNi1-xMnxO2-δ exhibited the highest rate capability. From the systematically investigated phase evolution behaviors, a higher activation energy as well as a slower rate of phase transition reaction for higher Mn contents phase were observed.