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1.
Spherical (Ni0.5Mn0.5)(OH)2 with different secondary particle size (3 μm, 10 μm in diameter) was synthesized by co-precipitation method. Mixture of the prepared hydroxide and lithium hydroxide was calcined at 950 °C for 20 h in air. X-ray diffraction patterns revealed that the prepared material had a typical layered structure with space group. Spherical morphologies with mono-dispersed powders were observed by scanning electron microscopy. It was found that the layered Li[Ni0.5Mn0.5]O2 delivered an initial discharge capacity of 148 mAh g−1 (3.0-4.3 V) though the particle sizes were different. Li[Ni0.5Mn0.5]O2 having smaller particle size (3 μm) showed improved area specific impedance due to the reduced Li+ diffusion path, compared with that of Li[Ni0.5Mn0.5]O2 possessing larger particle size (10 μm). Although the Li[Ni0.5Mn0.5]O2 (3 μm) was electrochemically delithiated to Li0.39[Ni0.5Mn0.5]O2, the resulting exothermic onset temperature was around 295 °C, of which the value is significantly higher than that of highly delithiated Li1−δCoO2 (∼180 °C).  相似文献   

2.
A novel Li[Ni0.67Co0.15Mn0.18]O2 cathode material encapsulated completely within a concentration-gradient shell was successfully synthesized via co-precipitation. The Li[Ni0.67Co0.15Mn0.18]O2 has a core of Li[Ni0.8Co0.15Mn0.05]O2 that is rich in Ni, a concentration-gradient shell having decreasing Ni concentration and increasing Mn concentration toward the particle surface, and a stable outer-layer of Li[Ni0.57Co0.15Mn0.28]O2. The electrochemical and thermal properties of the material were investigated and compared to those of the core Li[Ni0.8Co0.15Mn0.05]O2 material alone. The discharge capacity of the concentration-gradient Li[Ni0.67Co0.15Mn0.18]O2 electrode increased with increasing upper cutoff voltage to 4.5 V, and cells with this cathode material delivered a very high capacity, 213 mAh/g, with excellent cycling stability even at 55 °C. The enhanced thermal and lithium intercalation stability of the Li[Ni0.67Co0.15Mn0.18]O2 was attributed to the gradual increase in tetravalent Mn concentration and decrease in Ni concentration in the concentration-gradient shell layer.  相似文献   

3.
Sen Zhang 《Electrochimica acta》2007,52(25):7337-7342
Li[Ni1/3Co1/3Mn1/3]O2 cathode material for lithium ion batteries was prepared by mixing metal hydroxide, (Ni1/3Co1/3Mn1/3)(OH)2, with 6% excess LiOH followed by calcinations. The (Ni1/3Co1/3Mn1/3)(OH)2 with secondary particle of about 12 μm was prepared by hydroxide co-precipitation. The tap density of the obtained Li[Ni1/3Co1/3Mn1/3]O2 powder was 2.56 ± 0.21 g cm−3. The powder was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), particle size distribution (PSD) and galvanostatic charge-discharge cycling. The XRD pattern of Li[Ni1/3Co1/3Mn1/3]O2 revealed a well ordered hexagonal layered structure with low cation mixing. Secondary particles with size of 13-14 μm and primary particles with size of about 1 μm can be identified from the SEM observations. In the voltage range of 2.8-4.3 V, the initial discharge capacity of the Li[Ni1/3Co1/3Mn1/3]O2 electrode was 166.6 mAh g−1, and 96.5% of the initial capacity was retained after 50 charge-discharge cycling.  相似文献   

4.
Layered Li[Ni1/2Mn1/2]O2 was synthesized by an ultrasonic spray pyrolysis method. The Li[Ni1/2Mn1/2]O2 powder was characterized by means of X-ray diffraction, charge/discharge test, and cyclic voltammetry. The discharge capacity increases linearly with increase of the upper cut-off voltage limit and attains a high discharge capacity of 187 mA h g–1 between 2.8 and 4.6 V with excellent cyclability. A cyclic voltammetric study of the Li[Ni1/2Mn1/2]O2 electrode showed only one redox peak implying no structural phase change during cycling.  相似文献   

5.
In order to get homogeneous layered oxide Li[Ni1/3Mn1/3Co1/3]O2 as a lithium insertion positive electrode material, we applied the metal acetates decomposition method. The oxide compounds were calcined at various temperatures, which results in greater difference in morphological (shape, particle size and specific surface area) and the electrochemical (first charge profile, reversible capacity and rate capability) differences. The Li[Ni1/3Mn1/3Co1/3]O2 powders were characterized by means of X-ray diffraction (XRD), charge/discharge cycling, cyclic voltammetry and SEM. XRD experiment revealed that the layered Li[Ni1/3Mn1/3Co1/3]O2 material can be best synthesized at temperature of 800 °C. In that synthesized temperature, the sample showed high discharge capacity of 190 mAh g−1 as well as stable cycling performance at a current density of 0.2 mA cm−2 in the voltage range 2.3-4.6 V. The reversible capacity after 100 cycles is more than 190 mAh g−1 at room temperature.  相似文献   

6.
Layered Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) have been prepared by the mixed hydroxide and molten-salt synthesis method. The individual particles of synthesized materials have a sub-microsize range of 200-500 nm, and LiNi0.475Mn0.475Zr0.05O2 has a rougher surface than that of LiNi0.5Mn0.5O2. The Li/Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) electrodes were cycled between 4.5 and 2.0 V at a current density of 15 mA/g, the discharge capacity of both cells increased during the first ten cycles. The discharge capacity of the Li/LiNi0.475Mn0.475Zr0.05O2 cell increased from 150 to 220 mAh/g, which is 50 mAh/g larger than that of the Li/LiNi0.5Mn0.5O2 cell. We found that the oxidation of oxygen and the Mn3+ ion concerned this phenomenon from the cyclic voltammetry (CV). Thermal stability of the charged Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) cathode was improved by Zr doping.  相似文献   

7.
S. Zhang  C. Deng  B.L. Fu  L. Ma 《Powder Technology》2010,198(3):373-400
A carbonate co-precipitation method was employed to prepare spherical Li[Ni1/3Co1/3Mn1/3]O2 cathode material. The precursor, [Ni1/3Co1/3Mn1/3]CO3, was prepared using ammonia as chelating agent under CO2 atmosphere. The spherical Li[Ni1/3Co1/3Mn1/3]O2 was prepared by mixing the precalcined [Ni1/3Co1/3Mn1/3]CO3 with LiOH followed by high temperature calcination. The preparation conditions such as ammonia concentration, co-precipitation temperature, calcination temperature and Li/[Ni1/3Co1/3Mn1/3] ratio were varied to optimize the physical and electrochemical properties of the prepared Li[Ni1/3Co1/3Mn1/3]O2. The structural, morphological, and electrochemical properties of the prepared LiNi1/3Co1/3Mn1/3O2 were characterized by XRD, SEM, and galvanostatic charge-discharge cycling. The optimized material has a spherical particle shape and a well ordered layered structure, and it also has an initial discharge capacity of 162.7 mAh g− 1 in a voltage range of 2.8-4.3 V and a capacity retention of 94.8% after a hundred cycles. The optimized ammonia concentration, co-precipitation temperature, calcination temperature, and Li/[Ni1/3Co1/3Mn1/3] ratio are 0.3 mol L− 1, 60 °C, 850 °C, and 1.10, respectively.  相似文献   

8.
A positive electrode material for lithium ion battery applications was successfully synthesized using microwave irradiation. This microwave synthesis has several merits such as homogeneity of final product and much shorter reaction time compared to conventional synthetic methods. We synthesized spherical [Ni0.4Co0.2Mn0.4](OH)2 as a precursor by a co-precipitation method. The pelletized mixture of the precursor and lithium hydroxide was calcined under different reaction times and temperatures by applying 1200 W of microwave irradiation at 2.45 GHz. We determined the optimum conditions of microwave synthesis for positive electrode materials. The powders were characterized by X-ray diffraction, scanning electron microscopy, and electrochemical testing. The capacity, its retention, and thermal stability of Li[Ni0.4Co0.2Mn0.4]O2 synthesized by the microwave synthesis were comparable to the Li[Ni0.4Co0.2Mn0.4]O2 prepared by the high temperature calcination method.  相似文献   

9.
Synthetic optimization of Li[Ni1/3Co1/3Mn1/3]O2 via co-precipitation   总被引:1,自引:0,他引:1  
Li[Ni1/3Co1/3Mn1/3]O2 powders were synthesized from co-precipitated spherical metal hydroxide, (Ni1/3Co1/3Mn1/3)(OH)2. The preparation of metal hydroxide was significantly dependent on synthetic conditions, such as pH, amount of chelating agent, stirring speed, etc. The optimized condition resulted in (Ni1/3Co1/3Mn1/3)(OH)2, of which the particle size distribution was uniform and the particle shape was spherical, as observed by scanning electron microscopy. Calcination of the uniform metal hydroxide with LiOH at higher temperature led to a well-ordered layer-structured Li[Ni1/3Co1/3Mn1/3]O2, as confirmed by Rietveld refinement of X-ray diffraction pattern. Due to the homogeneity of the metal hydroxide, (Ni1/3Co1/3Mn1/3)(OH)2, the final product, Li[Ni1/3Co1/3Mn1/3]O2, was also significantly uniform, i.e., the average particle size was of about 10 μm in diameter and the distribution was relatively narrow. As a result, the corresponding tap-density was also high approximately 2.39 g cm−3, of which the value is comparable to that of commercialized LiCoO2. In the voltage range of 2.8-4.3, 2.8-4.4, and 2.8-4.5 V, the discharge capacities of Li[Ni1/3Co1/3Mn1/3]O2 electrode were 159, 168, and 177 mAh g−1, respectively. For elevated temperature operation (55 °C), the resulted capacity was of about 168 mAh g−1 with an excellent cyclability.  相似文献   

10.
Spherical Li[Ni1/3Co1/3Mn1/3]O2 powders were synthesized from LiOH·H2O and coprecipitated spherical metal hydroxide, (Ni1/3Mn1/3Co1/3)(OH)2 and coated with Al(OH)3. The Al(OH)3-coated Li[Ni1/3Co1/3Mn1/3]O2 showed a capacity retention of 80% at 320 mA g−1 (2 C-rate) based on 20 mA g−1 (0.1 C-rate), while the pristine Li[Ni1/3Co1/3Mn1/3]O2 delivered only 45% at the same current density. Also, unlike pristine Li[Ni1/3Co1/3Mn1/3]O2, the Al(OH)3-coated Li[Ni1/3Co1/3Mn1/3]O2 cathode exhibits excellent rate capability and good thermal stability.  相似文献   

11.
The layered Li[Li0.07Ni0.1Co0.6Mn0.23]O2 materials were synthesized by sol-gel method with glycine or citric acid as chelating agent. The prepared materials were characterized by means of XRD, SEM and Raman spectroscopy. Li/Li[Li0.07Ni0.1Co0.6Mn0.23]O2 cells were assembled and subjected to charge-discharge studies at different C rates, viz 0.2, 1, 2 and 4 C. Although the samples showed less discharge capacity at 4 C rate the fade in capacity per cycle is lesser than that of capacity fade at 0.2 C rate. The citric acid assisted sample is found to be superior in terms of discharge capacity, capacity retention rate and also in thermal stability to that of sample prepared with glycine as chelating agent.  相似文献   

12.
Layered Li[Li0.2Ni0.2Mn0.6]O2 powder was modified by coating its surface with amorphous Al(OH)3. Energy dispersive spectroscopy (EDS) showed that nano-sized Al(OH)3 powders were homogeneously dispersed in the parent Li[Li0.2Ni0.2Mn0.6]O2 powders. Al(OH)3 coated Li[Li0.2Ni0.2Mn0.6]O2 exhibited an greater retention capacity at higher rates compared to uncoated Li[Li0.2Ni0.2Mn0.6]O2. The low area specific impedance (ASI) value of the Al(OH)3 is the major factor for its higher rate performance. The 1.4 wt.% Al(OH)3 coated sample had an impedance of 41 Ω cm2 while uncoated Li[Li0.2Ni0.2Mn0.6]O2 had a 57 Ω cm2 at 30-80% state of charge. Electrochemical impedance spectroscopy (EIS) also showed that the Al(OH)3 coated sample had a lower charge transfer resistance (Rct) than the uncoated sample. Differential scanning calorimetry (DSC) analysis showed that Al(OH)3 coating improved the thermal stability. Al(OH)3 coating increased the onset temperature of thermal decomposition and reduced the amount of heat for the exothermic peak.  相似文献   

13.
Li[Li0.2Mn0.54Ni0.13Co0.13]O2 as a cathode material for Li-ion battery has been successfully prepared by co-precipitation (CP), sol–gel (SG) and sucrose combustion (SC) methods. The prepared materials were characterized by XRD, SEM, BET and electrochemical measurements. The XRD result shows that the Li[Li0.2Mn0.54Ni0.13Co0.13]O2 materials prepared by different methods all form a pure phase with good crystallinity. SEM images and BET data present that the SC-material exhibited the smallest particle size (ca. 0.1 μm) and the highest surface area (7.4635 m2 g−1). The tap density of SC-material is lower than that of CP- and SG-materials. The result of rate performance tests indicates that the SC-material showed the best rate capability with the highest discharge capacity of 178 mAh g−1 at 5.0 C, followed by SG-material and then CP-material. However, the cycling stability of SC-material tested at 0.1 and 0.5 C is relatively poor as compared to that of SG-material and CP-material. The result of EIS measurements reveals that large surface area and small particle size of the SC-electrode result in more SEI layer formation because of the increased side reactions with the electrolyte during cycling, which deteriorates the electrode/electrolyte interface and thus leads to the faster capacity fading of the SC-material.  相似文献   

14.
In attempts to prepare layered Li[Ni1/3Co1/3Mn1/3]O2, hydrothermal method was employed. The hydrothermal precursor, [Ni1/3Co1/3Mn1/3](OH)2, was synthesized via a coprecipitation route. The sphere-shaped powder precursor was hydrothermally reacted with LiOH aqueous solution at 170 °C for 4 days in autoclave. From X-ray diffraction and scanning electron microscopic studies, it was found that the as-hydrothermally prepared powders were crystallized to layered α-NaFeO2 structure and the particles had spherical shape. The as-prepared Li[Ni1/3Co1/3Mn1/3]O2 delivered an initial discharge of about 110 mA h g−1 due to lower crystallinity. Heat treatment of the hydrothermal product at 800 °C was significantly effective to improve the structural integrity, which consequently affected the increase in the discharge capacity to 157 (4.3 V cut-off) and 182 mA h g−1 (4.6 V cut-off) at 25 °C with good reversibility.  相似文献   

15.
The layered Li[Ni1/3Co1/3Mn1/3]O2 materials were synthesized by a spray pyrolysis method using citric acid as a polymeric agent. The Li[Ni1/3Co1/3Mn1/3]O2 powders were characterized by means of X-ray diffraction (XRD), charge/discharge cycling, cyclic voltammetry, and high-resolution transmission electron microscopy (TEM). The discharge capacity increases linearly with the increase of the upper cut-off voltage limit. TEM analysis showed that particles in the as-prepared powder possessed a polycrystalline structure. During cycling, the particle structure is mostly preserved although some surface grains on the polycrystalline particle became separated and transformed to the spinel phase.  相似文献   

16.
Hui Xia  M.O. Lai 《Electrochimica acta》2009,54(25):5986-5991
Kinetic and transport parameters of Li ion during its extraction/insertion into thin film LiNi0.5Mn0.5O2 free of binder and conductive additive were provided in this work. LiNi0.5Mn0.5O2 thin film electrodes were grown on Au substrates by pulsed laser deposition (PLD) and post-annealed. The annealed films exhibit a pure layered phase with a high degree of crystallinity. Surface morphology and thin film thickness were investigated by field emission scanning electron microscopy (FESEM). The charge/discharge behavior and rate capability of the thin film electrodes were investigated on Li/LiNi0.5Mn0.5O2 cells at different current densities. The kinetics of Li diffusion in these thin film electrodes were investigated by cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT). CV was measured between 2.5 and 4.5 V at different scan rates from 0.1 to 2 mV/s. The apparent chemical diffusion coefficients of Li in the thin film electrode were calculated to be 3.13 × 10−13 cm2/s for Li intercalation and 7.44 × 10−14 cm2/s for Li deintercalation. The chemical diffusion coefficients of Li in the thin film electrode were determined to be in the range of 10−12-10−16 cm2/s at different cell potentials by GITT. It is found that the Li diffusivity is highly dependent on the cell potential.  相似文献   

17.
A Li[Ni0.4Co0.3Mn0.3]O2 cathode was modified by applying a La2/3−XLi3XTiO3 (LLT) coating. Transmission electron microscope (TEM) images reveal that the coating layer consists of nanoparticles. The coated cathode demonstrated an enhanced rate capability, discharge capacity, and cyclic performance than the uncoated cathode. However, the influence of the coating upon these electrochemical properties is highly dependent upon the composition of the LLT coating layer. Coating layers having high La and low Li contents, such as La0.67TiO3, effectively improved the rate capability of the cathode. However, coating layers with a low La and high Li content greatly enhanced the discharge capacity of the cathode under high cut-off voltage (4.8 V) conditions. Overall, the thermal stability of the Li[Ni0.4Co0.3Mn0.3]O2 electrode was improved by the LLT coating. Storage tests confirmed that the La2/3−XLi3XTiO3 coating dramatically suppressed the dissolution of transition metals into the electrolyte.  相似文献   

18.
The layered LiNi0.5Mn0.5O2 was synthesized by wet-chemical method and characterized by X-ray diffraction and SQUID magnetometry. The powders adopted the α-NaFeO2 structure. The ferromagnetism observed below Tc = 140 K is attributed to the linear Ni2+(3a)-O-Mn4+(3b)-O-Ni2+(3a) magnetic paths, from which we derive that 7% of the nickel occupies the (3a) Wyckoff position in place of Li, constituting a Ni2+(3a) defect. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie-Weiss law agrees well with the combination of Ni2+ (S = 1) and Mn4+ (S = 3/2) spin-only values. Results of structural and magnetic properties of chemically delithiated sample are consistent with the electronic state Mn4+/Ni4+ and the high-spin configuration for Ni4+ ions. The LiNi0.5Mn0.5O2 electrode sintered at 900 °C delivers a capacity 166 mAh/g at 0.1C rate which is capacity retention of 95%.  相似文献   

19.
Layered Li[Li0.12NizMg0.32−zMn0.56]O2 oxide cathodes containing lithium atoms in the transition metal layers were synthesized and characterized using X-ray diffraction (XRD), galvanostatic cycling, and differential scanning calorimetry (DSC). The Li[Li0.12NizMg0.32−zMn0.56]O2 cathodes deliver a specific discharge capacity of about 190 mAh/g at room temperature and 236 mAh/g at 55 °C when cycled between 2.7 and 4.6 V versus Li/Li+. Excellent capacity retention and smooth potential profiles at room and elevated temperatures over extended cycles suggest that this material does not convert into a spinel structure.  相似文献   

20.
This work provides kinetic and transport parameters of Li-ion during its extraction/insertion into thin film LiNi0.5Mn1.5O4 free of binder and conductive additive. Thin films of LiNi0.5Mn1.5O4 (0.2 μm thick) were prepared on electronically conductive gold substrate utilizing the electrostatic spray deposition technique. High purity LiNi0.5Mn1.5O4 thin film electrodes were observed with cyclic voltammetry, to exhibit very sharp peaks, high reversibility, and absence of the 4 V signal related to the Mn3+/Mn4+ redox couple. The electrode subjected to 100 CV cycles of charge/discharge delivered a capacity of 155 mAh g−1 on the first cycle and sustained a good cycling behavior while retaining 91% of the initial capacity after 50 cycles. Kinetics and mass-transport of Li-ion extraction at LiNi0.5Mn1.5O4 thin film electrode were investigated by means of electrochemical impedance spectroscopy. The apparent chemical diffusion coefficient (Dapp) value determined from EIS measurements changed depending on the electrode potential in the range of 10−10-10−12 cm2 s−1. The Dapp profile shows two minimums at the potential values close to the peak potentials of the corresponding cyclic voltammogram.  相似文献   

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