Hydrothermal synthesis and electrochemical performance studies of Al2O3-coated LiNi1/3Co1/3Mn1/3O2 for lithium-ion batteries

LiNi_1/3Co_1/3Mn_1/3O₂ nanocrystallites were synthesized by a one-step hydrothermal method, and uniform second particles were formed by a subsequent calcination process. X-ray diffraction results indicate that the as-synthesized material can be indexed by α-NaFeO₂ layered structure with R-3 m space group. The results of Rietveld refinements show the I ₀₀₃/I ₁₀₄ value of the material is 2.032, and the nanostructured material presents low cation mixing, small cell volume, and a consequent suppression of lattice strain. The rate performances of the as-synthesized material can be further improved by coating Al₂O₃. The discharging capacity of Al₂O₃-coated material reaches 154.4 mAh g^?1, and the capacity retention maintains 80.3 % after 50 cycles at 5 C in the voltage range of 2.5 to 4.5 V, while those of the bare one is only 139.0 mAh g^?1 and 71.6 %, respectively. The transmission electron microcopy observation shows no zigzag layer exists on the surface of particle after cycles for Al₂O₃-coated LiNi_1/3Co_1/3Mn_1/3O₂. Compared to bare LiNi_1/3Co_1/3Mn_1/3O₂, the de-intercalation potential difference before and after cycles of Al₂O₃-coated one is smaller. This indicates that Al₂O₃ coating can reduce the electrochemistry polarization in the electrode bulk.     

Studies of the electrochemical properties and thermal stability of LiNi1/3Co1/3Mn1/3O2/LiFePO4 composite cathodes for lithium ion batteries

A series of LiNi_1/3Co_1/3Mn_1/3O₂/LiFePO₄ composite cathodes with the LiFePO₄ mass content ranging from 10 to 30 wt% were prepared by ball milling in order to combine the merits of layered LiNi_1/3Co_1/3Mn_1/3O₂ and olivine LiFePO₄. The structure and morphology of the samples were characterized by X-ray diffraction and scanning electron microscope. The composite cathodes exhibited improved electrochemical performance compared with pristine LiNi_1/3Co_1/3Mn_1/3O₂. Among all the composite cathodes, the one with 20 wt% of LiFePO₄ showed the best electrochemical performance in terms of discharge capacity, cycle stability, and rate capability. Electrochemical impedance spectroscopy showed that mixing of LiFePO₄ in LiNi_1/3Co_1/3Mn_1/3O₂ decreased the internal resistance of the electrode, retarded the formation of SEI film, and facilitated the charge transfer reaction. Differential scanning calorimetry showed that the composite cathode had better thermal stability than pristine LiNi_1/3Co_1/3Mn_1/3O₂.     

Synthesis of cation-substituted LiNi0.8Co0.1Mn0.1O2 from laterite

Cation-substituted LiNi_0.8Co_0.1Mn_0.1O₂ sample is synthesized from purified laterite lixivium, without any extraction process. ICP analysis shows that partial Cr, Mg, and Al element incorporate in the compound. XRD and Rietveld refinement shows that proper Cr, Mg, and Al co-substitution could lead to a synergistic reaction to form a kind of highly ordered layered LiNi_0.8Co_0.1Mn_0.1O₂ with low Ni/Li mixing degree. From EDAX and XPS studies, it could be found that Cr and Al may prefer to enrich on the surface of cathode material, and the surface concentration of unstable Ni ions decrease. Electrochemical studies confirm that the cation-substituted LiNi_0.8Co_0.1Mn_0.1O₂ sample, synthesized from laterite, exhibits improved rate ability and cycling property compared with the pristine sample. This method is a simple and effective way to utilize laterite and synthesize cathode material.     

ZrO2 coating of LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

ZrO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ materials were prepared by hydroxide precipitation. The structure and electrochemical properties of the ZrO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ were investigated using X-ray diffraction, scanning electron microscope, and charge–discharge tests, indicating that the lattice structure of LiNi_1/3Co_1/3Mn_1/3O₂ were unchanged after the coating but the cycling stability was improved. As the coating amount increased from 0.0 to 0.5 mol.%, the initial capacity of the coated LiNi_1/3Co_1/3Mn_1/3O₂ decreased slightly; however, the cycling stability increased remarkably over the cut-off voltages of 2.5~4.3 V and the capacity retention reached 99.5% after 30 cycles at the coating amount of 0.5 mol.%. ZrO₂ coating also improved the cycling stability of LiNi_1/3Co_1/3Mn_1/3O₂ over wider cut-off voltage of 2.5~4.6 V.     

LiNi1/3Co1/3Mn1/3O2 cathode materials for LIB prepared by spray pyrolysis I: the spectral, structural, and electro-chemical properties

Layered lithium ion battery cathode material LiNi_1/3Co_1/3Mn_1/3O₂ with uniform particle size of about 6 μm was synthesized by a spray pyrolysis method. Infrared and X-ray diffraction analyses show that the pyrolysis at 1,000 °C for 2 s in the tube furnace eliminates nearly all the organic components but is still not enough for the complete crystallization of LiNi_1/3Co_1/3Mn_1/3O₂ materials. Therefore, further annealing at 850 °C is needed. The prepared LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials show excellent electrochemical performances. By increasing the C-rates, the cell shows discharge capacities of 159.3, 148.2, 133.7, and 125.7 mAh g^?1 at 0.1, 0.2, 0.5, and 1C rates, respectively. Only 2.1 mAh g^?1 capacity loss is observed when back to 0.1C rate. Moreover, LiNi_1/3Co_1/3Mn_1/3O₂ cathode retains 96, 97.7, 97.1, 94.5, and 97.1 % of its initial discharge capacities after 20 cycles at 0.1, 0.2, 0.5, 1, and back to 0.1C rates, respectively. More than 97 % coulombic efficiencies are observed at all the current densities in 20 cycles.     

Synthesis of spherical LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

Spherical LiNi_1/3Co_1/3Mn_1/3O₂ was successfully prepared by controlled crystallization. The preparation started with the spherical coprecipitate of Ni_1/3Co_1/3Mn_1/3CO₃ from NiSO₄, CoSO₄, MnSO₄, NH₄HCO₃, and NH₃·H₂O, followed by pyrolysis of Ni_1/3Co_1/3Mn_1/3CO₃ at 600°C for 3 h. The X-ray diffraction analysis showed that the homogeneous cubic (Ni_1/3Co_1/3Mn_1/3)₃O₄ was obtained after the pyrolysis. Spherical LiNi_1/3Co_1/3Mn_1/3O₂ was obtained by sintering of the mixture of as-obtained (Ni_1/3Co_1/3Mn_1/3)₃O₄ and LiOH·H₂O at 900°C for 6 h in air. As-prepared spherical LiNi_1/3Co_1/3Mn_1/3O₂ presented initial discharge capacity of 162.9 mA h g⁻¹ and capacity retention of 98% at 50th cycle.     

Structural and electrochemical properties of LiNi1/3Co1/3Mn1/3O2 material prepared by a two-step synthesis via oxalate precursor

LiNi_1/3Co_1/3Mn_1/3O₂ (LNMCO) powders were formed by a two-step synthesis including preparation of an oxalate precursor by ??chimie douce?? followed by a solid-state reaction with lithium hydroxide. The product was characterized by TG-DTA, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), Raman spectroscopy, electron spin resonance (ESR), and SQUID magnetometry. XRD data revealed well-crystallized layered LNMCO with ??-NaFeO₂-type structure (R-3?m space group). Morphology studied by SEM and TEM shows submicronic particles of 400?C800?nm with a tendency to agglomerate. The local structure investigated by vibrational spectroscopy (FTIR, Raman), ESR, and SQUID measurements confirms the well-crystallized lattice with a cation disorder of 2.6% Ni²⁺ ions in Li(3b) sites. Electrochemical tests were carried out in the potential range 2.5?C4.5?V vs. lithium metal on samples heated at 900?°C for 12?h. Initial discharge capacity is 154 mAh/g at C/5, while a capacity of 82 mAh/g is still delivered at 10 C by the two-step synthesized LiNi_1/3Co_1/3Mn_1/3O₂ as cathode material.     

TiO2 coating of LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

TiO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ materials were prepared by the hydrolyzation of Ti(OBu)₄. The impact of TiO₂ coating on the structure and electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ was investigated using X-ray diffraction, scanning electron microscope, and charge–discharge tests. The results indicated that TiO₂ coating did not affect the lattice of LiNi_1/3Co_1/3Mn_1/3O₂, but exhibited obvious effects on its discharge capacity and cycling stability. As coated TiO₂ increased from 0.0 to 2.0 mol%, the initial capacity of samples decreased slightly, but the cycling stability over 2.5∼4.3 V increased remarkably. The capacity retention reached 99.5% at the 50th cycle at a coating amount of 2.0 mol%.     

Structural, transport and electrochemical properties of LiNi1 − yCoyMn0.1O2 and Al, Mg and Cu-substituted LiNi0.65Co0.25Mn0.1O2 oxides

LiNi_{1 - y − z}Co_yMn_zO₂ (y = 0.25, 0.35, 0.5, 0.6; z = 0.1, 0.2), LiNi_0.63Cu_0.02Co_0.25Mn_0.1O₂, LiNi_0.65Co_0.25Mn_0.08Al_0.02O₂, LiNi_0.65Co_0.25Mn_0.08Mg_0.02O₂ and LiNi_0.65Co_0.25Mn_0.08Al_0.01Mg_0.01O₂ cathode materials were synthesized by a soft chemistry EDTA-based method. Structural and transport properties of pristine and delithiated materials (Li_xNi_0.65Co_0.25Mn_0.1O₂, Li_xNi_0.55Co_0.35Mn_0.1O₂ and LiNi_0.63Cu_0.02Co_0.25Mn_0.1O₂ oxides) are presented. In the considered group of oxides there is no correlation between electrical conductivity and the a parameter (M-M distance in the octahedra layers). The results of electrochemical performance of cathode materials are presented. The best stability during first 10 cycles was obtained for Li/Li_xNi_0.63Cu_0.02Co_0.25Mn_0.1O₂ cell due to enhanced kinetics of intercalation process.     

LiNi1/3Co1/3Mn1/3O2 cathode materials for LIB prepared by spray pyrolysis. II. Li+ diffusion kinetics

Layered lithium ion battery cathode material LiNi_1/3Co_1/3Mn_1/3O₂ with a uniform particle size of about 6 μm was synthesized by a spray pyrolysis method. The lithium ion diffusion kinetics in LiNi_1/3Co_1/3Mn_1/3O₂ composite cathode were systematically studied by the ratio of potentio-charge capacity to galvano-charge capacity method, galvanostatic intermittent titration technique, electrochemical impedance spectroscopy, and potential step chronoamperometry methods. The variations of lithium ion diffusion coefficients obtained by the four methods show a close similarity. They vary in the range of 10^?8 to 10^?10 cm² s^?1, with a maximum at 4.1- to 4.2-V voltage level.     

The effects of copper and titanium co-substitution on LiNi<Subscript>0.6</Subscript>Co<Subscript>0.15</Subscript>Mn<Subscript>0.25</Subscript>O<Subscript>2</Subscript> for lithium ion batteries

The Li(Ni_0.6Co_0.15Mn_0.25)_1?x (CuTi) _x O₂ (x = 0.00, 0.01, 0.02, 0.03) cathode materials were synthesized via a hydroxide co-precipitation method followed by a solid-state reaction. The elementary composition, crystal structure features, morphology, and electrochemical performances of the powders were investigated in detail by inductively coupled plasma-atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), galvanostatic charge/discharge test, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), respectively. The results of XRD and Rietveld refinements demonstrate that Cu and Ti co-substitution does not destroy the crystal structure, but can decrease cation ordering level and improve structural integrity. Electrochemical results show that Cu and Ti addition also results in an improved rate and cycling performances compared to pristine LiNi_0.6Co_0.15Mn_0.25O₂. An increase in rate performance and cycle stability upon copper and titanium co-substitution is related to the better hexagonal structure and enhanced kinetics of the intercalation process. Especially, Li(Ni_0.6Co_0.15Mn_0.25)_0.99(CuTi)_0.01O₂ exhibits the best rate performance and cycle stability among all samples with discharge specific capacity of 178.8 mAh/g and capacity retention of 90.6% after 30 cycles at 0.2C, which are higher than those of other materials.     

High rate performance of Li[Ni1/3Co1/3Mn1/3]O2 synthesized via co-precipitation method by different precipitators

In the present study, we investigated the effect of three different precipitators (NaOH, Na₂CO₃ and (NH₄)₂CO₃) on the synthesized layered Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode materials via co-precipitation method. The obtained compounds were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and galvanostatic charge–discharge measurements. The XRD patterns analysis showed that all the resulted Li[Ni_1/3Co_1/3Mn_1/3]O₂ materials possess a layered hexagonal structure. It was found that at high discharge rate (2C), the prepared Li[Ni_1/3Co_1/3Mn_1/3]O₂ system using Na₂CO₃ as the precipitator exhibits better cycling performance in the charge–discharge tests compared to others, indicating that Na₂CO₃ is an optimum precipitator. After 100 cycles at 2C discharge rate in the voltage range from 2.8 to 4.5 vs. Li/Li⁺, the Li[Ni_1/3Co_1/3Mn_1/3]O₂ system using Na₂CO₃ as the precipitator retains 97% of its initial discharge capacity.     

The properties research of ferrum additive on Li [Ni<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>] O<Subscript>2</Subscript> cathode material for lithium ion batteries

Li[Ni_1/3Co_(1-x)/3Mn_1/3Fe _x/3] O₂(x?=?0.0, 0.1, 0.3, 0.5, 0.7, and 0.9) cathode materials have been synthesized via hydroxide co-precipitation method followed by a solid state reaction. Thermogravimetry (TG) and differential thermal analysis (DTA) measurements were utilized to determine the calcination temperature of precursor sample. The crystal structure features were characterized by X-ray diffraction (XRD). The electrochemical properties of Li[Ni_1/3Co_(1-x)/3Mn_1/3Fe _x/3]O₂ were compared by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy(EIS), and galvanostatic charge/discharge test. Electrochemical test results indicate that Li[Ni_1/3Co_0.9/3Mn_1/3Fe_0.1/3] O₂ decrease charge transfer resistance and enhance Li⁺ ion diffusion velocity and thus improve cycling and high-rate capability compared with Li[Ni_1/3Co_1/3Mn_1/3]O₂. The initial discharge specific capacity of Li[Ni_1/3Co_0.9/3Mn_1/3Fe_0.1/3] O₂ was 178.5 mAh/g and capacity retention was 87.11 % after 30 cycles at 0.1C, with the battery showing good cycle performance.     

Enhanced electrochemical properties and thermal stability of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> by surface modification with Eu<Subscript>2</Subscript>O<Subscript>3</Subscript>

Layered LiNi_1/3Co_1/3Mn_1/3O₂ cathode material is synthesized via a sol-gel method and subsequently surface-modified with Eu₂O₃ layer by a wet chemical process. The effect of Eu₂O₃ coating on the electrochemical performances and thermal stability of LiNi_1/3Co_1/3Mn_1/3O₂@Eu₂O₃ cells is investigated systematically by the charge/discharge testing, cyclic voltammograms, AC impedance spectroscopy, and DSC measurements, respectively. In comparison, the Eu₂O₃-coated sample demonstrates better electrochemical performances and thermal stability than that of the pristine one. After 100 cycles at 1C, the Eu₂O₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ cathode demonstrates stable cyclability with capacity retention of 92.9 %, which is higher than that (75.5 %) of the pristine one in voltage range 3.0–4.6 V. Analysis from the electrochemical measurements reveals that the remarkably improved performances of the surface-modified composites are mainly ascribed to the presence of Eu₂O₃-coating layer, which could efficiently suppress the undesirable side reaction and increasing impedance, and enhance the structural stability of active material.     

Improvement of cycling and thermal stability of LiNi<Subscript>0.8</Subscript>Mn<Subscript>0.1</Subscript>Co<Subscript>0.1</Subscript>O<Subscript>2</Subscript> cathode material by secondly treating process

(Ni_0.8Mn_0.1Co_0.1)(OH)₂ and Co(OH)₂ secondly treated by LiNi_0.8Mn_0.1Co_0.1O₂ have been prepared via co-precipitation and high-temperature solid-state reaction. The residual lithium contents, XRD Rietveld refinement, XPS, TG-DSC, and electrochemical measurements are carried out. After secondly treating process, residual lithium contents decrease drastically, and occupancy of Ni in 3a site is much lower and Li/Ni disorder decreases. The discharge capacity is 193.1, 189.7, and 182 mAh g^?1 at 0.1 C rate, respectively, for LiNi_0.8Mn_0.1Co_0.1O₂-AP, -NT, and -CT electrodes between 3.0 and 4.2 V in pouch cell. The capacity retention has been greatly improved during gradual capacity fading of cycling at 1 C rate. The noticeably improved thermal stability of the samples after being treated can also be observed.     

Synthesis and characterization of La0.7Sr0.3Mn1−x TixO3 manganites

The structural, electrical and magnetic properties of the La_0.7Sr_0.3Mn_1?x Ti_xO₃ system characterized by rhombohedral lattice distortions are studied. Substitution of titanium for manganese weakens ferromagnetism and leads to an increased resistivity. Using x-ray Rietveld full-profile refinement data and ferromagnetic resonance spectra, it is demonstrated that titanium substitution for manganese occurs with charge compensation according to the equation Mn⁴⁺ → Ti⁴⁺ and with a simultaneous decrease in the oxygen nonstoichiometry as the value of x increases.     

Factors limiting the electrochemical performance of oxide cathodes

An overview of the current understanding of the factors limiting the electrochemical performances of the layered, spinel, and olivine oxide cathodes is presented with a particular focus on the chemical and structural instabilities. The wide variations in the reversible capacity limits of LiMO₂ layered oxide cathodes (140 mA h/g for LiCoO₂ vs 160–200 mA h/g for LiNi_1/3Mn_1/3Co_1/3O₂ and LiNi_0.5Mn_0.5O₂) could be explained on the basis of differences in chemical instabilities arising from an overlap of M^n+/(n+1)+:3d and O²⁻:2p bands. Degree of cation disorder and lithium extraction rate are found to influence the type of phases formed for the chemically delithiated Li_1−xMO₂ and the electrochemical rate capability. On the other hand, the lattice parameter difference between the two cubic phases formed during the charge–discharge process is found to play a significant role on the capacity retention, rate capability, and storage characteristics of the spinel oxide cathodes in addition to the well-known Mn dissolution problem. Despite excellent structural and chemical stabilities, the olivine LiFePO₄ suffers from poor electrical conductivity and consequent low rate capability.     

Optical properties of bulk Zn1−xCoxO magnetic semiconductors

Polycrystalline Zn_1−xCo_xO (x=0, 0.02, 0.05, 0.10 and 0.15) oxides have been synthesized by solid state reaction via sintering ZnO and Co powders in open air. X-ray diffraction analyses using Rietveld refinement indicate that a stoichiometric single phase with a wurtzite-like structure was found in Zn_1−xCo_xO samples with x up to 0.10. The elemental mapping using energy dispersive X-ray spectroscopic analyses presents a uniform distribution of Co. Optical transmittance measurements show that several extra absorption bands appear in the Co-doped ZnO, which is due to the transitions between the crystal-field-split 3d levels of tetrahedral Co²⁺ substituting Zn²⁺ ions. Raman measurements show that limited host lattice defects are induced by Co doping. Magnetization measurements reveal that the Co-doped ZnO samples are paramagnetic due to the absence of free carriers and in low temperature the dominant magnetic interaction is nearest-neighbor antiferromagnetic.     

The studies on structural and thermal properties of delithiated LixNi1/3Co1/3Mn1/3O2 (0 < x ≤ 1) as a cathode material in lithium ion batteries

The structural and thermal properties of the delithiated Li_xNi_1/3Co_1/3Mn_1/3O₂ (0 < x ≤ 1) material have been investigated by using diffraction and thermoanalytical techniques such as XRD and TG-DSC methods. XRD result shows that the delithiated materials maintain the O3-type structure with defined stoichiometric number at the range of 0.24 < x ≤ 1, exhibiting good crystal structural stability. The cobalt and nickel ions in the delithiated materials change their valence state (i.e. Co³⁺ to Co⁴⁺ and Ni³⁺ to Ni⁴⁺) when x < 0.49; the irreversible changes of the transformation may affect the first cycle of charge–discharge efficiency of the materials. A comparison of the results of TG-DSC with TPD-MS shows that the irreversible change of oxygen species during the delithiation process of Li_xNi_1/3Co_1/3Mn_1/3O₂ have great influence on the structural and thermal stability and reversibility of the materials.     

Spin reversal and magnetization jumps in ErMexMn1−xO3 perovskites (Me=Ni,Co)

The erbium-based manganite ErMnO₃ has been partially substituted at the manganese site by the transition-metal elements Ni and Co. The perovskite orthorhombic structure is found from x(Ni)=0.2–0.5 in the nickel-based solid solution ErNi_xMn_1−xO₃, while it can be extended up to x(Co)=0.7 in the case of cobalt, provided that the synthesis is performed under oxygenation conditions to favor the presence of Co³⁺. Presence of different magnetic entities (i.e., Er³⁺, Ni²⁺, Co²⁺, Co³⁺, Mn³⁺, and Mn⁴⁺) leads to quite unusual magnetic properties, characterized by the coexistence of antiferromagnetic and ferromagnetic interactions. In ErNi_xMn_1−xO₃, a critical concentration x_crit(Ni)=1/3 separates two regimes: spin-canted AF interactions predominate at x<x_crit, while the ferromagnetic behavior is enhanced for x>x_crit. Spin reversal phenomena are present both in the nickel- and cobalt-based compounds. A phenomenological model based on two interacting sublattices, coupled by an antiferromagnetic exchange interaction, explains the inversion of the overall magnetic moment at low temperatures. In this model, the ferromagnetic transition-metal lattice, which orders at T_c, creates a strong local field at the erbium site, polarizing the Er moments in a direction opposite to the applied field. At low temperatures, when the contribution of the paramagnetic erbium sublattice, which varies as T⁻¹, gets larger than the ferromagnetic contribution, the total magnetic moment changes its sign, leading to an overall ferrimagnetic state. The half-substituted compound ErCo_0.50Mn_0.50O₃ was studied in detail, since the magnetization loops present two well-identified anomalies: an intersection of the magnetization branches at low fields, and magnetization jumps at high fields. The influence of the oxidizing conditions was studied in other compositions close to the 50/50=Mn/Co substitution rate. These anomalies are clearly connected to the spin inversion phenomena and to the simultaneous presence of Co²⁺ and Co³⁺ magnetic moments. Dynamical aspects should be considered to well identify the high-field anomaly, since it depends on the magnetic field sweep rate.