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.     

Simple co-precipitation synthesis of high-voltage spinel cathodes with different Ni/Mn ratios for lithium-ion batteries

The high-voltage spinel is a promising cathode material in next generation of lithium-ion batteries. Samples LiNi_0.5???xMn_1.5?+?xO₄ (x?=?0, 0.05, 0.1) are synthesized by a simple co-precipitation method, in which pH value and temperature conditions do not need control. In the simple co-precipitation method, NaHCO₃ solution is poured into transition metal solution to produce precursor. Ni and Mn are distributed uniformly in the products. The as-prepared samples are composed of ~?200 nm primary particles. Samples LiNi_0.5???xMn_1.5?+?xO₄ (x?=?0, 0.05, 0.1) are also tested to study the effects of different Ni/Mn ratios. Sample LiNi_0.5Mn_1.5O₄ delivers discharge capacities of 130 mAh g^?1 at 0.2 C. The decreasing of Ni/Mn ratio in samples reduces specific capacity. With the decreasing of Ni/Mn ratios in spinel, amount of Mn³⁺ are increased. Attributed to its high Mn³⁺ contents, sample LiNi_0.4Mn_1.6O₄ delivers the highest discharge capacity of 106 mAh g^?1 at a large current density of 15 C, keeping 84.5% of that at 0.2 C rate. With the increasing of Ni/Mn ratios in spinel, cycling performance is improved. Sample LiNi_0.5Mn_1.5O₄ shows the best cycling stability, keeping 94.4% and 90.4% of the highest discharge capacities after 500 cycles at 1 C and 1000 cycles at 5 C.     

Improving the rate performance and stability of LiNi<Subscript>0.6</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.2</Subscript>O<Subscript>2</Subscript> in high voltage lithium-ion battery by using fluoroethylene carbonate as electrolyte additive

Fluoroethylene carbonate (FEC) is investigated as the electrolyte additive to improve the electrochemical performance of high voltage LiNi_0.6Co_0.2Mn_0.2O₂ cathode material. Compared to LiNi_0.6Co_0.2Mn_0.2O₂/Li cells in blank electrolyte, the capacity retention of the cells with 5 wt% FEC in electrolytes after 80 times charge-discharge cycle between 3.0 and 4.5 V significantly improve from 82.0 to 89.7%. Besides, the capacity of LiNi_0.6Co_0.2Mn_0.2O₂/Li only obtains 12.6 mAh g^?1 at 5 C in base electrolyte, while the 5 wt% FEC in electrolyte can reach a high capacity of 71.3 mAh g^?1 at the same rate. The oxidative stability of the electrolyte with 5 wt% FEC is evaluated by linear sweep voltammetry and potentiostatic data. The LSV results show that the oxidation potential of the electrolytes with FEC is higher than 4.5 V vs. Li/Li⁺, while the oxidation peaks begin to appear near 4.3 V in the electrolyte without FEC. In addition, the effect of FEC on surface of LiNi_0.6Co_0.2Mn_0.2O₂ is elucidated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The analysis result indicates that FEC facilitates the formation of a more stable surface film on the LiNi_0.6Co_0.2Mn_0.2O₂ cathode. The electrochemical impedance spectroscopy (EIS) result evidences that the stable surface film could improve cathode electrolyte interfacial resistance. These results demonstrate that the FEC can apply as an additive for 4.5 V high voltage electrolyte system in LiNi_0.6Co_0.2Mn_0.2O₂/Li cells.     

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.     

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.     

An investigation on the unsatisfactory rate capability of spherical LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> particles prepared by using Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> as a precipitant

Spherical LiNi_1/3Co_1/3Mn_1/3O₂ particles were successfully synthesized using Na₂CO₃ as a precipitant. Electrochemical measurements indicate that the as-synthesized spherical particles deliver a high reversible capacity of above 180 mAh g^?1 at 0.1 C in the voltage range of 2.8–4.4 V and display an excellent cyclic performance at 0.5 C. However, unsatisfactory rate capability was detected for the as-prepared spherical particles. The reason for the unsatisfactory rate capability was investigated through a comparison of the properties of the as-synthesized spherical particles versus the ball-milled samples via a combination of specific surface areas test, electronic conductivity measurement, and electrochemical impedance spectroscopy. The results show that both the rate capabilities of cathode materials and the electronic conductivities of the mixtures of active material, conductive additive, and binder are highly improved when the secondary spherical particles were broken, indicating that the poor electronic conductivity of electrode caused by the large secondary spherical particles with a great amount of nano-pores is a significant factor for the unsatisfactory rate capability.     

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 and electrochemical properties of Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript> cathode material for lithium-ion battery

The layered Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ lithium-rich manganese-based solid solution cathode material has been synthesized by a simple solid-state method. The as-prepared material has a typical layered structure with R-3m and C2/m space group. The synthesized Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ has an irregular shape with the size range from 200 to 500 nm, and the primary particle of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ has regular sphere morphology with a diameter of 320 nm. Electrochemical performances also have been investigated. The results show that the cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ prepared at 900 °C for 12 h has a good electrochemical performance, which can deliver a high initial discharge capacity of 233.5, 214.2, 199.3, and 168.1 mAh g^?1 at 0.1, 0.2, 0.5, and 1 C, respectively. After 50 cycles, the capacity retains 178.0, 166.3, 162.1, and 155.9 mAh g^?1 at 0.1, 0.2, 0.5, and 1 C, respectively. The results indicate that the simple method has a great potential in synthesizing manganese-based cathode materials for Li-ion batteries.     

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.     

Facile synthesis of hierarchical porous Ni-rich LiNi<Subscript>0.6</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.2</Subscript>O<Subscript>2</Subscript> cathode material with superior high-rate capability

A hierarchical porous nickel-rich LiNi_0.6Co_0.2Mn_0.2O₂ cathode is successfully prepared for the first time using a facile ammonia-induced method, wherein ammonia molecules play a key role in fabricating the complex architecture, and neither templates nor precipitants are employed. Hierarchical flower-like precursor with ultra-thin nanosheets is formed during the ammonia-induced reaction, and then, the porous product is obtained during the sintering process. The X-ray diffraction pattern demonstrates that the sample has a well-defined α-NaFeO₂ structure with very low-cation disorder. The peculiar hierarchical porous morphology and ideal structure endow this material-enhanced electrochemical performance. It delivers discharge capacities of 173, 138, 111, 97, and 82 mAh g^?1 at 0.1 C, 1 C, 5 C, 10 C, and 20 C, respectively, and maintains 91 % of its initial discharge capacity after 100 cycles at 1 C. The results reveal that this method is facile and feasible to synthesize high-rate Nickel-rich material.