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1.
The effects of Al substitution for Ni or (and) Mn in LiNi0.5Mn1.5O4 spinel on the structures and electrochemical properties are investigated. Powders of LiNi0.5Mn1.5O4, Li0.95Ni0.45Mn1.5Al0.05O4, LiNi0.475Mn1.475Al0.05O4 and Li1.05Ni0.5Mn1.45Al0.05O4 are synthesized by a thermopolymerization method. Their structures and electrochemical properties are studied by X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, cyclic voltammetry and galvanostatic charge–discharge testing. The introduction of Al in these LiNi0.5Mn1.5O4 samples has resulted in structure variation, and greatly improved their cyclic performance and rate capability. The effects of Al substitutions for Ni and Mn in the LiNi0.5Mn1.5O4 are different. Compared with LiNi0.5Mn1.5O4, Li0.95Ni0.45Mn1.5Al0.05O4 demonstrates higher specific capacity at room temperature but faster capacity fading at elevated temperatures. Li1.05Ni0.5Mn1.45Al0.05O4 displays a lower discharge capacity but better capacity retention at 55 °C. Moreover, the cyclic performance and rate capability of the Ni-substituted Li0.95Ni0.45Mn1.5Al0.05O4, Ni/Mn co-substituted LiNi0.475Mn1.475Al0.05O4 and Mn-substituted Li1.05Ni0.5Mn1.45Al0.05O4 at room temperature are similar, and have improved substantially compared with the Al-free LiNi0.5Mn1.5O4 sample.  相似文献   

2.
The feasibility of the Pechini method for the preparation of LiNi1/3Mn1/3Co1/3O2 with characteristics appropriate for Li-ion battery positive electrodes was investigated. The method involves formation of one single chemically homogenous precursor material and thus permits reduced calcination times and minimal lithium evaporation. The physical and electrochemical properties of the materials were investigated with variation in final calcination temperature. Chemical analysis showed that the materials could be prepared with high crystallinity and yet little or no loss of lithium. The material calcined at 1000 °C showed the highest specific capacity—180 mAh g−1 when cycled between 4.5 and 3 V, and it maintained its capacity over 50 cycles. The advantage of this material over those prepared at 800 and 900 °C can probably be attributed to the fact that the degree of crystallinity, crystallite size and size of the primary particles increase with calcination temperature, and that the powder attains a more suitable morphology which promotes electronic connectivity to all of the oxide material. A temperature above 1000 °C should however not be used as indicated by an abrupt change in lattice parameters and decrease in electronic conductivity when going from 1000 to 1050 °C. The Pechini method presents an attractive option for the preparation of LiNi1/3Mn1/3Co1/3O2 positive electrode material.  相似文献   

3.
We reported here on the synthesis, the crystal structure and the study of the structural changes during the electrochemical cycling of layered LiNi0.1Mn0.1Co0.8O2 positive electrode material. Rietveld refinement analysis shows that this material exhibits almost an ideal α-NaFeO2 structure with practically no lithium-nickel disorder. The SQUID measurements confirm this structural result and evidenced that this material consists of Ni2+, Mn4+ and Co3+ ions.Unlike LiNiO2 and LiCoO2 conventional electrode materials, there was no structural modification upon lithium removal in the whole 0.42 ≤ x ≤1.0 studied composition range. The peaks revealed in the incremental capacity curve were attributed to the successive oxidation of Ni2+ and Co3+ while Mn4+ remains electrochemically inactive.  相似文献   

4.
Li2ZnTi3O8 fibers are synthesized by thermally treating electrospun Zn(CH3COO)2/LiOAc/TBT/PVP fibers and utilized as an energy storage material for rechargeable lithium-ion batteries. The material is characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and thermal analysis. Scanning electron microscopy results show that the Li2ZnTi3O8 fibers have an average diameter of 200 nm. Electrochemical properties of the material are evaluated using cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy. The results show that as-prepared Li2ZnTi3O8 has a high specific discharge capacity of 227.6 mAh g−1 at the 2nd cycle. Its electrochemical performance at subsequent cycles shows good cycling capacity and rate capability. The obtained results thus strongly support that the electrospinning method is an effective method to prepare Li2ZnTi3O8 anode material with higher capacity and rate capability.  相似文献   

5.
The perovskite-type LaFe0.5Ni0.5O3 belonging to the rhombohedral (space group R-3c) crystal structure has been synthesized for which we have identified a magnetic transition at T1 =?8?K corresponding to the minimum observed in the derivative of temperature dependent magnetization. A bifurcation in the ZFC and FC curves is observed below T1 that suggests a frustrated magnetic behavior. The non-zero moment above T1 hints the possibility of the presence of a high-temperature magnetic transition in the material. The resistivity of LaFe0.5Ni0.5O3 evolves as a function of temperature similar to that of a semiconductor. Mott's variable range hopping governs the conduction mechanism of the material. Presence of various anisotropy terms and inhomogeneous magnetic interactions lead to the presence of antiferromagnetic and ferromagnetic interfaces, which eventually causes a magnetic exchange bias and magnetic hysteresis in resistivity. We have also observed direction dependent magnetoresistance in the material.  相似文献   

6.
A crystalline LiNi0.65Co0.25Mn0.10O2 electrode material was synthesized by the combustion method at 900 °C for 1 h. Rietveld refinement shows less than 3% of Li/Ni disorder in the structure. Lithium extraction involves only the Ni2+/Ni4+ redox couple while Co3+ and Mn4+ remain electrochemically inactive. No structural transition was detected during cycling in the whole composition range 0 < x < 1.0. Furthermore, the hexagonal cell volume changes by only 3% when all lithium was removed indicating a good mechanical stability of the studied compound. LiNi0.65Co0.25Mn0.10O2 has a discharge capacity of 150 mAh/g in the voltage range 2.5-4.5 V, but the best electrochemical performance was obtained with an upper cut-off potential of 4.3 V. Magnetic measurements reveal competing antiferromagnetic and ferromagnetic interactions - varying in strength as a function of lithium content - yielding a low temperature magnetically frustrated state. The evolution of the magnetic properties with lithium content confirms the preferential oxidation of Ni ions compared to Co3+ and Mn4+ during the delithiation process.  相似文献   

7.
The solid solutions LiCoO2-LiNi1/2Mn1/2O2-Li2MnO3 with higher Mn content have been prepared by a spray drying method between 750 and 950 °C and their electrochemical performances have also been characterized. The effects of the Li content on the structure and electrochemical performance of the samples have been studied. It was found that their lattice parameters a, c and V increase with the increase in Ni content and the decrease in Co content. The solid solutions xLiCoO2-yLiNi1/2Mn1/2O2-(1−xy)Li2MnO3 with x = 0.18, 0.27 and y = 0.2 have the largest discharge capacity, which is more than 200 mAh/g in the voltages of 3.0-4.6 V. It is believed that the optimum Co content x in xLiCoO2-yLiNi1/2Mn1/2O2-(1−xy)Li2MnO3 is between 0.2 and 0.3 in the charge-discharge voltage range of 3.0-4.6 V. The solid solutions xLiCoO2-yLiNi1/2Mn1/2O2-(1−xy)Li2MnO3 with x = 0.18-0.36 and y = 0.2 have the excellent cycling performance and the capacity retention attains to almost 100% after 50 cycles. Moreover, it is found that the discharge capacity gradually increases with the increment of cycle number especially in the initial 10 cycles. XRD showed that the layered structure has been kept all the time in 20 cycles, which is perhaps the reason why the sample has the excellent cycling performance.  相似文献   

8.
In this work the synthesis of a nickel doped cubic manganese spinel has been studied for application as cathode material in secondary lithium batteries. Six different experimental approaches have been tested in order to carry out a screening of the various possible synthetic routes. The used synthetic strategies were wet chemistry (WC), solid state (SS), combustion synthesis (CS), cellulose-based sol-gel synthesis (SG-C), ascorbic acid-based sol-gel synthesis (SG-AA) and resorcinol/formaldehyde-based sol-gel synthesis (SG-RF). The goal of our study is to obtain insights about how the synthesis conditions can be modified in order to achieve a material with improved electrochemical performances in such devices, especially in high current operating regimes. The synthesized materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), atomic absorption, inductively coupled plasma (ICP-MS) atomic emission spectroscopy, surface area measurements and tested as high voltage cathodes in Li-ion electrochemical devices.  相似文献   

9.
LiNi1/2Mn1/2O2 electrodes with layered structure were synthesized by solid-state reaction between lithium hydroxide and mixed Ni,Mn oxides obtained from co-precipitated Ni,Mn carbonates and hydroxides and freeze-dried Ni,Mn citrates. The temperature of the solid-state reaction was varied between 800 and 950 °C. This method of synthesis allows obtaining oxides characterized with well-crystallized nanometric primary particles bounded in micrometric aggregates. The extent of particle agglomeration is lower for oxides obtained from freeze-dried Ni,Mn citrates. The local Mn4+ surrounding in the transition metal layers was determined by X-band electron paramagnetic resonance (EPR) spectroscopy. It has been found that local cationic distribution is consistent with α,β-type cationic order with some extent of disordering that depends mainly on the precursors used. The electrochemical extraction and insertion of lithium was tested in lithium cells using Step Potential Electrochemical Spectroscopy. The electrochemical performance of LiNi1/2Mn1/2O2 oxides depends on the precursors used, the synthesis temperature and the potential range. The best electrochemical response was established for LiNi1/2Mn1/2O2 prepared from the carbonate precursor at 900 °C. The changes in local environment of Mn4+ ions during electrochemical reaction in both limited and extended potential ranges were discussed on the basis of ex situ EPR experiments.  相似文献   

10.
Layered LiNi0.6Co0.2Mn0.2O2 materials were synthesized at different sintering temperatures using spray-drying precursor with molar ratio of Li/Me = 1.04 (Me = transition metals). The influences of sintering temperature on crystal structure, morphology and electrochemical performance of LiNi0.6Co0.2Mn0.2O2 materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and charge-discharge test. As a result, material synthesized at 850 °C has excellent electrochemical performance, delivering an initial discharge capacity of 173.1 mAh g− 1 between 2.8 and 4.3 V at a current density of 16 mA g− 1 and exhibiting good cycling performance.  相似文献   

11.
LiNi0.5Mn0.5O2 was heat-treated under high oxygen-pressure and Ar-reducing conditions, and then the cathode properties, thermodynamic stability and average and local structures were investigated. From X-ray diffraction and ICP measurements, it was found that the pristine LiNi0.5Mn0.5O2 had a single phase of the layered rock-salt structure although the Ni content was slightly rich compared with the nominal one. These characteristics were kept even after the heat-treatments. Charge–discharge cycle tests clarified that the cycle performance of LiNi0.5Mn0.5O2 was improved by both the reducing and oxidizing treatments. From neutron diffraction and X-ray absorption fine structure measurements, the local distortion around the transition metal, especially Ni, was supposed to be one of the important factors to determine the cathode properties. It was also found that the sample with higher thermodynamic stability exhibited better capacity retention in the discharge–charge cycle tests.  相似文献   

12.
A series of LiNi0.5Mn0.5−xCoxO2 (0 ≤ x ≤ 0.5) compounds was prepared by a solid state reaction, and their structure, surface state and electrochemical characteristics were also investigated by XRD, XPS, EIS and charge-discharge cycling. The non-equivalent substitution of cobalt for manganese induced an increase in the average valence of nickel, thereby shrinking in the lattice volume. Moreover, Co non-equivalent substitution could not only reduce the impurity content but also significantly decreased the charge transfer resistance, thereby improving the rate capabilities.  相似文献   

13.
Layered Li(Ni1/3Co1/3Mn1/3)O2 was prepared by mixed hydroxide method and characterised by means of X-ray diffraction, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry and charge-discharge cycling. The hexagonal lattice parameters obtained for the compound are: a=2.864 and c=14.233 Å. XPS studies show that the predominant oxidation states of Ni, Co and Mn in the compound are 2+, 3+ and 4+, respectively with small content of Ni3+ and Mn3+ ions. Initial discharge capacity of 160 mAh/g was obtained in the range 2.5-4.4 V and at a specific current of 30 mA/g of which 143 mAh/g was retained at the end of 40 charge-discharge cycles. At lower current (10 mA/g) and in the voltage window 2.5-4.7 V, discharge capacity of 215 mAh/g is obtainable. From the voltage profile and cyclic voltammetry, the redox processes occurring at ∼3.8 and ∼4.6 V are assigned to the Ni2+/4+ and Co3+/4+ couples, respectively.  相似文献   

14.
G.Q. Liu  Qilu  W. Li 《Electrochimica acta》2005,50(9):1965-1968
Spinel compound LiNi0.5Mn1.5O4 was synthesized by a chemical wet method. Mn(NO3)2, Ni(NO3)2·6H2O, NH4HCO3 and LiOH·H2O were used as the starting materials. At first, Mn(NO3)2 and Ni(NO3)2·6H2O reacted with NH4HCO3 to produce a precursor, then the precursor reacted with LiOH·H2O to synthesize product LiNi0.5Mn1.5O4. The product showed a single spinel phase under appropriate calcination conditions, and exhibited a high voltage plateau at about 4.6-4.8 V in the charge/discharge process. The LiNi0.5Mn1.5O4 had a discharge specific capacity of 118 mAh/g at about 4.6 V and 126 mAh/g in total in the first cycle at a discharge current density of 2 mA/cm2. After 50 cycles, the total discharge capacity was above 118 mAh/g.  相似文献   

15.
Anatase TiO2 nanowires containing minor TiO2(B) phase were prepared by a hydrothermal chemical reaction followed by the post-heat treatment at 400 °C. The phase structure and morphology were analyzed by X-ray diffraction, Raman scattering, transmission electron microscope, and field-emission scanning electron microscopy. The electrochemical properties were investigated by employing constant current discharge-charge test, cyclic voltammetry, and electrochemical impedance techniques. These nanowires exhibited high rate capacity of 280 mAh g−1 even after 40 cycles, and the coulombic efficiency was approximately 98%, indicating excellent cycling stability and reversibility. The electrochemical impedance spectra showed a stable kinetic process of the electrode reaction. These results indicated that the TiO2 nanowires have promising application for high energy density lithium-ion batteries.  相似文献   

16.
Single phase Li9V3(P2O7)3(PO4)2 is synthesized at 750 °C via solid-state reaction method for the first time. The Rietveld refinement results show that the trigonal system (space group: ) with the lattice parameters a = 0.9724 nm, c = 1.3596 nm are obtained. Its intrinsic electrical conductivity of 1.43 × 10−8 S cm−1 is higher than that of LiFePO4 and as the same order of Li3V2(PO3)4. The electrochemical measurement results show that there are two plateaus (3.77 V and 4.51 V) and three plateaus (3.77 V, 4.51 V and 4.75 V) in the potential ranges of 2.0–4.6 V and 2.0–4.8 V, respectively. In the range of 2.0–4.6 V, two discharge plateaus (4.46 V and 3.74 V) can be observed and 110 mAh g−1 of discharge capacity is achieved. The Rietveld refinement result of the X-ray diffraction (XRD) data at the end of discharge after the first cycle suggests that the structural reversibility can be retained during electrochemical reactions in Li9V3(P2O7)3(PO4)2. In the range of 2.0–4.8 V, almost six lithium ions are extracted and the trigonal structure is still recovered after 30 cycles. Therefore, this novel layered vanadium monodiphosphate offers a promising candidate as cathode material for lithium-ion batteries.  相似文献   

17.
Layered Li[Ni0.5Mn0.5]O2 materials with high homogeneity and crystallinity were prepared using high speed ball milling. The Li[Ni0.5Mn0.5]O2 electrode delivered a high discharge capacity of 152 mA h g−1 between 2.8 and 4.3 V with excellent cycleability. The TEM analysis showed that the Li[Ni0.5Mn0.5]O2 electrode went through a considerable morphological change without altering its initial layered structure while the electrode retained its initial discharge capacity even after 50 cycles.  相似文献   

18.
The layered LiNi0.7Co0.3O2 cathode material was synthesized by the combustion method using sucrose as fuel at 800 °C for 1 h, which leads to homogeneous size distribution with sub-micron particle size. The characterization of this material was realized using X-ray diffraction, scanning electron microscopy and completed by magnetic measurements. The Rietveld refinement shows the presence of 2.6% extra nickel in the interslab space. The presence of nickel ions in the lithium layers was confirmed by magnetization measurements. The 90° Ni-O-Ni ferromagnetic coupling is the main magnetic interactions. Lithium extraction from this phase occurs without major structural modifications. Cycling tests have shown a very good cycling stability at various current rates. Furthermore, this material delivers high reversible capacity of about 150 mAh/g in the 2.8-4.4 V range at the C/20.  相似文献   

19.
A simple and effective method, ethylene glycol-assisted co-precipitation method, has been employed to synthesize LiNi0.5Mn1.5O4 spinel. As a chelating agent, ethylene glycol can realize the homogenous distributions of metal ions at the atomic scale and prevent the growth of LiNi0.5Mn1.5O4 particles. XRD reveals that the prepared material is a pure-phase cubic spinel structure (Fd3m) without any impurities. SEM images show that it has an agglomerate structure with the primary particle size of less than 100 nm. Electrochemical tests demonstrate that the as-prepared LiNi0.5Mn1.5O4 possesses high capacity and excellent rate capability. At 0.1 C rate, it shows a discharge capacity of 137 mAh g−1 which is about 93.4% of the theoretical capacity (146.7 mAh g−1). At the high rate of 5 C, it can still deliver a discharge capacity of 117 mAh g−1 with excellent capacity retention rate of more than 95% after 50 cycles. These results show that the as-prepared LiNi0.5Mn1.5O4 is a promising cathode material for high power Li-ion batteries.  相似文献   

20.
The presented work compared the etching behavior between combustion synthesized Ti3AlC2 (SHS-Ti3AlC2) and pressureless synthesized Ti3AlC2 (PLS-Ti3AlC2). Because the former had a more compact structure, it was harder to be etched than PLS-Ti3AlC2 under the same conditions. When served as anode material for Li-ion batteries, SHS-Ti3C2 showed much lower capacity than PLS-Ti3C2 at 1?C (52.7 and 87.4?mAh?g?1, respectively) due to the smaller d-spacing. Furthermore, Potentiostatic Intermittent Titration Technique (PITT) was used to determine the Li-ion chemical diffusion coefficient (DLi+) of Ti3C2 in the range of 10?10 ??10?9 cm2 s?1, indicating that Ti3C2 could exhibit an excellent diffusion mobility for Li-ion.  相似文献   

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