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.     

Enhanced electrochemical performances of LiNi0.5Co0.2Mn0.3O2 cathode material co-coated by graphene/TiO2

The electrochemical performances of LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) layered cathode material, such as poor rate capacity and cycling stability caused by undesirable intrinsic conductivity and low rate of lithium ion transportation, are not fairly good especially at elevated rate and cut-off voltage. To improve these properties, in this study, the co-coating layer of graphene and TiO₂ was constructed on NCM523 surface. The graphene/TiO₂ coating layer could effectively prevent hydrofluoric acid (HF) attacks, suppress the side reaction, accelerate the lithium ion diffusion and facilitate the electron migration. The enhancement of cycle performance and rate capacity was contributed to the uniform co-modified surface, interacting each other and thus exhibiting synergistic effects.     

Effects of Ca doping on the electrochemical properties of LiNi0.8Co0.2O2 cathode material

LiNi_0.8Co_0.2O₂ and Ca-doped LiNi_0.8Co_0.2O₂ cathode materials were synthesized via a rheological phase reaction method. It is found that the Ca doping significantly improves reversible capacity, cycling performance, thermal stability and rate capability. The Ca-doped LiNi_0.8Co_0.2O₂ cathode material maintains nearly its initial discharge capacity up to 100 cycles at room temperature. It also delivers an initial discharge capacity of 183 mA h g^− 1 and still keeps 131 mA h g^− 1 even after 120 cycles at 60 °C. These results, together with the X-ray diffraction and electrochemical impedance spectroscopy analysis, reveal that Ca²⁺ ions occupy Li⁺ ion sites to form Ca_Li defects and lithium vacancies (V_Li′), which reduce the resistance and increases conductivity of LiNi_0.8Co_0.2O₂.     

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.     

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%.     

Enhanced electrochemical performances of layered LiNi0.5Mn0.5O2 as cathode materials by Ru doping for lithium-ion batteries

Ionics - The pristine and Ru-doped LiNi0.5Mn0.5O2 cathode materials are synthesized by a wet chemical method, followed by a high-temperature calcination process. The influence of Ru substitution on...     

Structural, thermal and electrochemical properties of chromium-substituted LiNi0.8Co0.2O2

LiCr_yNi_0.8−yCo_0.2O₂ compositions, where y=0.000, 0.010, 0.025, 0.040, 0.050, 0.075 and 0.100, were synthesized via a conventional ceramic route. X-ray diffraction studies indicated cation mixing for the compositions with y ≥ 0.05. Cyclic voltammetric studies revealed that the systems were reversible only when y was lower than 0.05. High levels of substitutions with Cr resulted in highly irreversible systems, either due to cation mixing or the displacement of the substituent ions to the lithium inter-slab regions, or both. The charge-discharge characteristics of LiCr_yNi_0.8−yCo_0.2O₂ were similar to those of the unsubstituted material over ten cycles. All the other substituted compositions showed much lower capacities and reduced cyclability. LiCr_0.025Ni_0.775Co_0.2O₂ gave a first-cycle capacity of 169 mAh/g in the 3.0 to 4.4 V window at a 0.1 C rate, fading to 156 mAh/g in the tenth cycle. Differential scanning calorimetric studies revealed that substituting with chromium produced no benefit to thermal stability. The structural, thermal and electrochemical properties of the pristine and Cr-substituted LiNi_0.8Co_0.2O₂ compositions are discussed.     

Improvement of electrochemical properties of MgO-coated LiNi0.4Co0.2Mn0.4O2 cathode materials for lithium ion batteries

The surface of LiNi_0.4Co_0.2Mn_0.4O₂ cathode is coated using MgO coating materials. The electrochemical properties of the coated materials are investigated as a function of the pH value of the coating solution and the composition of coating materials. Their microscopic structural features have been investigated using scanning electron microscopy and X-ray diffraction. The electrochemical properties of the samples were monitored using coin-cell by galvanostatic charge–discharge cycling test, EDS test, EIS test, and cyclic voltammetry. The coating solution with pH?=?10.5 is found to be favorable for the formation of stable coating layers, which enhances the electrochemical properties. In contrast, 2 % MgO-coated LiNi_0.4Co_0.2Mn_0.4O₂ shows better cycle performance and rate capability than the bare sample. Such enhancements are attributed to the presence of a stable MgO layer which acts as the interfacial stabilizer on the surface of LiNi_0.4Co_0.2Mn_0.4O₂.     

Malonic acid-assisted synthesis of LiNi0.8Co0.2O2 cathode active material for lithium-ion batteries

Polycrystalline LiNi_0.8Co_0.2O₂ was synthesized by a solution route with malonic acid as the complexing agent. The effects of temperature, duration of heat treatment, pH of the precursor solution, and the nature of the solvent employed on the performance characteristics of the product were studied. It was observed that a 12-hour 800 °C heat treatment protocol was necessary to obtain products with optimal electrochemical characteristics. Furthermore, an excess lithium stoichiometry of 1.05 was found to be detrimental to the performance of the cathode material. The beneficial effect of ethanol as a solvent over water on the product characteristics is explained by the presence of solvent molecules in the coordination sphere of the cations. A pH of 7, at which malonic acid is complexed completely with the cations without interference from other nucleophiles, was found to be ideal for the synthesis of the cathode active material from aqueous solutions. With ethanol as the medium, the product formed by a 12-h calcination at 800 °C yielded a first-cycle capacity of 173 mAh/g and a tenth-cycle capacity of 169 mAh/g.     

Improving the cycle stability and rate performance of LiNi0.91Co0.06Mn0.03O2 Ni-rich cathode material by La2O3 coating for Lithium-ion batteries

In this wok, a uniform layer of La₂O₃ is coated on the surface of LiNi_0.91Co_0.06Mn_0.03O₂ Ni-rich cathode material by using a wet coating process. The XPS and EDX analysis confirms the presence of La₂O₃ coating on the surface of NCM. The coated samples deliver the superior electrochemical performance, 0.2 wt % La₂O₃ (LaO-0.2) NCM exhibits discharge capacity of 202.7 mAh g⁻¹ in 1^st cycle and delivered the cycle stability of 87.2% after 100 cycles. Besides, the enhanced capacity retention, LaO-0.2 has delivered very high discharge capacity of 80.3 mAh g⁻¹ at very high C-rate of 5C while the pristine sample shows very low discharge capacity (33.4 mAh g⁻¹). CV results shows the significant suppression in the intensity of H2–H3 which indicates the superior electrochemical stability of LaO-0.2 NCM. Thus, we can confirm that La₂O₃ coating is promising technique to achieve superior electrochemical performance in the long term cycling process.     

Synthesis of LiNi0.6Co0.2Mn0.2O2 cathode material by a carbonate co-precipitation method and its electrochemical characterization

Using Na₂CO₃ and Me(NO₃)₂ (Me = Ni, Co and Mn) as starting materials, the precursor of LiNi_0.6Co_0.2Mn_0.2O₂ cathode material for lithium rechargeable batteries has been synthesized by carbonate co-precipitation. The precursor was mixed with Li₂CO₃ and heated in air. Thermogravimetric analysis (TG–DTA), laser particle size analysis, X-ray diffraction (XRD) and electron scanning microscopy (SEM) were employed to study the reaction process and the structures of the powders. The D₅₀ of precursor was 2.509 μm and the distribution was relatively narrow. The optimum calcination temperature was 850–900 °C. Galvanostatic cell cycling and cyclic voltammetry were also used to evaluate the electrochemical properties. The initial discharge capacity for the powders calcined at 900 °C was about 180 mA h/g at room temperature when cycled between 2.8 and 4.3 V at 0.2 C rate.     

C-rate and temperature dependence of electrochemical performance of Li[Co0.1Ni0.15Li0.2Mn0.55]O2 cathode materials before and after Co3(PO4)2 coating

Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ was synthesized, as a cathode material with high capacity, by a simple combustion method followed by annealing at 800?°C. Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ cathode materials were coated with lithium-active Co₃(PO₄)₂ to improve the electrochemical performance of rechargeable lithium batteries. Morphologies and physical properties of Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ before and after the Co₃(PO₄)₂ coating were analyzed with a scanning electron microscope equipped with an energy dispersive X-ray spectroscope. Transmission electron microscopy, powder X-ray diffraction, and Brunauer?CEmmett?CTeller surface area analyses were also carried out. The electrochemical performances of Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ cathode material before and after Co₃(PO₄)₂ coating were evaluated by galvanostatic charge?Cdischarge testing at different charge and discharge densities. The temperature dependence of the cathode material before and after Co₃(PO₄)₂ coating was investigated at 0, 10, 20, 30, 40, and 50?°C at a rate of 0.1?C. Co₃(PO₄)₂-Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ exhibited good electrochemical performance under high C-rate and experimental temperature conditions. The enhanced electrochemical performances were attributed to the formation of a lithium-active Co₃(PO₄)₂-coating layer on Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂.     

Suppression of structural degradation of LiNi0.9Co0.1O2 cathode at 90 °C by AlPO4-nanoparticle coating

This study examined the electrochemical and structural stability of ∼1.5 wt.% AlPO₄-coated LiNi_0.9Co_0.1O₂. The AlPO₄-coated LiNi_0.9Co_0.1O₂ retained ∼60% of the original capacity after 50 cycles, compared with the ∼30% capacity retention of the bare LiNi_0.9Co_0.1O₂. The discharge profiles and cyclic voltammograms from 4.5 V at 90 °C for 4 h showed enhanced structural stability. Scanning electron microscopy and X-ray diffraction revealed that the AlPO₄-coated LiNi_0.9Co_0.1O₂ had less degradation than the bare LiNi_0.9Co_0.1O₂.     

Synthesis and electrochemical performance of LiNi0.6Co0.2Mn0.2O2/reduced graphene oxide cathode materials for lithium-ion batteries

A LiNi_0.6Co_0.2Mn_0.2O₂/reduced graphene oxide (RGO) composite with RGO content of 1.2 % was prepared by a simple spray-drying method instead of high-energy ball milling method. The composite has been characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, energy dispersive spectroscopy, and charge/discharge test. The X-ray diffractometry result showed that composite possessed a typical hexagonal structure. The RGO sheets served as efficient electronically conductive frameworks benefitting from its 2D structure and outstanding electronic conductivity. The scanning electron microscope and transmission electron microscopy verified that LiNi_0.6Co_0.2Mn_0.2O₂ particles were wrapped with RGO sheets, which facilitated electronic conductivity between particles. The electrochemical results indicated that composite delivered a higher discharge capacity at various discharge rates. The cycling performance was also evaluated. The composite exhibited better cycling performance than pristine sample. Electrochemical impedance spectroscopy showed that the RGO can greatly reduce the charge transfer resistance. The results here gave clear evidence of RGO to improve electrochemical performance.     

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.     

Characterization of Na-substituted LiNi1/3Co1/3Mn1/3O2 cathode materials for lithium-ion battery

Highly crystalline layered Li_1?xNa_xNi_1/3Co_1/3Mn_1/3O₂ (x?=?0, 0.001, 0.01, 0.03, 0.05) materials are synthesized by molten salts method and characterized by scanning electron microscopy, inductively coupled plasma (ICP), X-ray diffraction, Rietveld refinement, and electrochemical measurement, respectively. ICP, SEM, and EDS results show that Na ions are incorporated in LiNi_1/3Co_1/3Mn_1/3O₂. Rietveld refinement results show that suitable Na substitution leads to stable layered structure by full Na occupying in Li layer and further attributes to low cation mixing. Electrochemical studies demonstrate that the Na-substituted LiNi_1/3Co_1/3Mn_1/3O₂ shows improved rate capability and cycling performance compared to that of pure LiNi_1/3Co_1/3Mn_1/3O₂.     

Structural and electrochemical studies on thin film LiNi0.8Co0.2O2 by PLD for micro battery

Thin film of LiNi_0.8Co_0.2O₂ (LNCO) has been prepared by Pulsed Laser Deposition (PLD) technique at various post annealing temperatures. XRD results of LNCO thin film deposited on both Pt and Si substrates reveal relatively good crystalline nature at 500 °C which is in good agreement with the electrochemical results. ICP-AES composition analysis indicates 10 to 5% Li loss in the post annealed (400–700 °C) LNCO/Pt thin films; however the as prepared LNCO/Pt films show 17% excess of Li which are comparable with the LNCO target results. SEM analysis indicates phase separation at 600 °C and porous nature at 700–800 °C for LNCO/Pt films. Cyclic voltammetry (CV) scans of LiNi_0.8Co_0.2O₂ film post annealed at 500 °C show a pair of main cathodic and anodic peaks at 3.64 and 3.4 V, respectively with a narrow peak separation reveals good stability upon cycling. Whereas the LNCO films annealed at 600 °C and 700 °C indicate an additional anodic peak at lower potential besides a pair of major peaks which may be due to the phase separated morphology as evidenced from SEM analysis. Based on the structural and electrochemical results, a lithium-ion micro cell has been constructed with LNCO/Li_3.4V_0.6Si_0.4O₄(LVSO)/SnO configuration with the thickness of 1.535 µm and its electrochemical properties have been studied.     

Sonochemical synthesis of LiNi0.5Mn1.5O4 and its electrochemical performance as a cathode material for 5 V Li-ion batteries

LiNi_0.5Mn_1.5O₄ was synthesized as a cathode material for Li-ion batteries by a sonochemical reaction followed by annealing, and was characterized by XRD, SEM, HRTEM and Raman spectroscopy in conjunction with electrochemical measurements. Two samples were prepared by a sonochemical process, one without using glucose (sample-S1) and another with glucose (sample-S2). An initial discharge specific capacity of 130 mA h g⁻¹ is obtained for LiNi_0.5Mn_1.5O₄ at a relatively slow rate of C/10 in galvanostatic charge–discharge cycling. The capacity retention upon 50 cycles at this rate was around 95.4% and 98.9% for sample-S1 and sample-S2, respectively, at 30 °C.     

Vibrational spectroscopy and electrochemical properties of LiNi0.7Co0.3O2 cathode material for rechargeable lithium batteries

We are reporting the synthesis and characterization of solid solutions of the LiNiO₂ and LiCoO₂ system. Substitution of cobalt for nickel in the LiNi_1−yCo_yO₂ phases provides significant improvements in the two-dimensionality of the crystal lattice and ease the large scale synthesis. This structural effect improves the reversibility of the lithium intercalation-deintercalation process. We have evaluated the vibrational spectra and electrochemical properties of LiNi_0.7Co_0.3O₂ (charge-discharge profiles and cyclic voltammetry) and compared the results with those of the end members, i.e., LiNiO₂ and LiCoO₂. The local environment of cations against oxygen neighboring atoms has been determined. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997