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1.
Layered Li0.7[M1/6Mn5/6]O2 (M=Li, Ni) was synthesized using a sol-gel method. P2-Na0.7[M1/6Mn5/6]O2 precursor was first synthesized by a sol-gel method, and then O2-Li0.7[M1/6Mn5/6]O2 was prepared by an ion exchange of Li for Na in P2-Na0.7[M1/6Mn5/6]O2 precursor. From charge/discharge curves, it was seen that Li0.7[Li1/6Mn5/6]O2 has two plateaus similar to those observed from a spinel structure, but Li0.7[Ni1/6Mn5/6]O2 holds a single plateau as observed from a typical layered structure. It was considered that Li0.7[Li1/6Mn5/6]O2 undergoes a phase transformation from layered to spinel structure during the charge/discharge cycle, but Li0.7[Ni1/6Mn5/6]O2 maintains O2-layered structure after the cycles. Li0.7[Ni1/6Mn5/6]O2 was higher in discharge capacity and retention rate than Li0.7[Li1/6Mn5/6]O2.  相似文献   

2.
Li0.7[Li1/12Ni1/12Mn5/6]O2 and Li0.7[Li1/12Ni1/12Mn5/6]O2-ySy (y=0.1, 0.2, 0.3) powders were synthesized by using a sol-gel method. As-prepared samples showed typical rhombohedral O3 layered structure. The shape of the initial discharge curve for the samples was almost equal to that of the layered structure. However, the electrode materials were transferred from layered to spinel structures with cycling. At the first cycle, Li0.7[Li1/12Ni1/122Mn25/6]O2 and Li0.7[Li1/12Ni1/12 Mn5/6]O1.9S0.1, Li0.7[Li1/12Ni1/12Mn5/6]O1.8S0.2, and Li0.7[Li1/12Ni1/12Mn5/6]O1.7S0.3 delivered the discharge capacities of 238, 230,224, and 226 mAh/g, respectively, with their capacity fading rates of 0.34, 0.21, 0.12, 0.25%/cycle, respectively. The partial substitutions of Ni and S for Mn and O in Li0.7[Li1/12Ni1/12Mn1/12]O2 significantly enhanced the electrochemical properties of the lithium manganese oxide materials.  相似文献   

3.
Li0.7[Li1/6Mn5/6]O2 and Li0.7[Li1/12Ni1/12Mn5/6]O2 powders were synthesized by a sol-gel method. The powders had a typically rhombohedral layered O3 structure. Both the samples were nanometer-sized powders and the size of Li0.7[Li1/12Ni1/12Mn5/6]O2 was smaller than that of Li0.7[Li1/6Mn5/6]O2. The discharge curve shape of both the sample electrodes was almost equal to that of the layered structure. However, the electrode materials were transferred from layered to spinel structures with increasing the cycle number. Li/Li0.7[Li1/6Mn5/6]O2 and Li0.7[Li1/12Ni1/12Mn5/6]O2 cells initially delivered a discharge capacity of 261 and 238 mAh/g, respectively. The capacities of Li/Li0.7[Li1/6Mn5/6]O2 and Li0.7 [Li1/12Ni1/12Mn5/6]O2 after the 45th cycle were 174 and 221 mAh/g, respectively, corresponding to the retentions of 67% and 93%. The nanostructure of the synthesized powders seems to result in high initial discharge capacity as well as in the suppression of the discharge capacity fading by providing high surface area needed for Li ion reaction. In Ni doped-Li0.7[Li1/12Ni1/12Mn5/6]O2, the capacity fading was reduced by suppressing the oxidation state of Mn from 4+ to 3+ due to the role of Ni ion doped.  相似文献   

4.
Recently, there have been many reports on efforts to improve the rate capability and discharge capacity of lithium secondary batteries in order to facilitate their use for hybrid electric vehicles and electric power tools. In the present work, we present a ZrO2-coated Li[Li1/6Mn1/2Co1/6Ni1/6]O2. The bare Li[Li1/6Mn1/2Co1/6Ni1/6]O2 shows a high initial discharge capacity of 224 mAh g−1 at a 0.2 C rate. Owing to the stability of ZrO2, it was possible to enhance the rate capability and cyclability. After 1 wt% ZrO2 coating, the ZrO2-coated Li[Li1/6Mn1/2Co1/6Ni1/6]O2 showed a high discharge capacity of 115 mAh g−1 after 50 cycles under a 6 C rate, whereas the bare Li[Li1/6Mn1/2Co1/6Ni1/6]O2 showed a discharge capacity of only 40 mAh g−1 and very poor cyclability under the same conditions. Based on results of XRD and EIS measurements, it was found that the ZrO2 suppressed impedance growth at the interface between the electrodes and electrolyte and prevented collapse of the layered hexagonal structure.  相似文献   

5.
Layered metastable lithium manganese oxides, Li2/3[Ni1/3−xMn2/3−yMx+y]O2 (x = y = 1/36 for M = Al, Co, and Fe and x = 2/36, y = 0 for M = Mg) were prepared by the ion exchange of Li for Na in P2-Na2/3[Ni1/3−xMn2/3−yMx+y]O2 precursors. The Al and Co doping produced the T#2 structure with the space group Cmca. On the other hand, the Fe and Mg doped samples had the O6 structure with space group R-3m. Electron diffraction revealed the 1:2 type ordering within the Ni1/3−xMn2/3−yMx+yO2 slab. It was found that the stacking sequence and electrochemical performance of the Li cells containing T#2-Li2/3[Ni1/3Mn2/3]O2 were affected by the doping with small amounts of Al, Co, Fe, and Mg. The discharge capacity of the Al doped sample was around 200 mAh g−1 in the voltage range between 2.0 and 4.7 V at the current density of 14.4 mA g−1 along with a good capacity retention. Moreover, for the Al and Co doped and undoped oxides, the irreversible phase transition of the T#2 into the O2 structure was observed during the initial lithium deintercalation.  相似文献   

6.
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   

7.
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   

8.
In this research, we studied the first cycle characteristics of Li[Ni1/3Co1/3Mn1/3]O2 charged up to 4.7 V. Properties, such as valence state of the transition metals and crystallographic features, were analyzed by X-ray absorption spectroscopy and X-ray and neutron diffractions. Especially, two plateaus observed around 3.75 and 4.54 V were investigated by ex situ X-ray absorption spectroscopy. XANES studies showed that the oxidation states of transition metals in Li[Ni1/3Co1/3Mn1/3]O2 are mostly Ni2+, Co3+ and Mn4+. Based on neutron diffraction Rietveld analysis, there is about 6% of all nickel divalent (Ni2+) ions mixed with lithium ions (cation mixing). Meanwhile, it was found that the oxidation reaction of Ni2+/Ni4+ is related to the lower plateau around 3.75 V, but that of Co3+/Co4+ seems to occur entire range of x in Li1−x[Ni1/3Co1/3Mn1/3]O2. Small volume change during cycling was attributed to the opposite variation of lattice parameter “c” and “a” with charging-discharging.  相似文献   

9.
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   

10.
Spinel Li4Mn5O12 was prepared by a sol–gel method. The manganese oxide and activated carbon composite (MnO2-AC) were prepared by a method in which KMnO4 was reduced by activated carbon (AC). The products were characterized by XRD and FTIR. The hybrid supercapacitor was fabricated with Li4Mn5O12 and MnO2-AC, which were used as materials of the two electrodes. The pseudocapacitance performance of the Li4Mn5O12/MnO2-AC hybrid supercapacitor was studied in various aqueous electrolytes. Electrochemical properties of the Li4Mn5O12/MnO2-AC hybrid supercapacitor were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the hybrid supercapacitor has electrochemical capacitance performance. The charge/discharge test showed that the specific capacitance of 51.3 F g−1 was obtained within potential range of 0–1.3 V at a charge/discharge current density of 100 mA g−1 in 1 mol L−1 Li2SO4 solution. The charge/discharge mechanism of Li4Mn5O12 and MnO2-AC was discussed.  相似文献   

11.
《Ceramics International》2021,47(24):34611-34618
An O3 type Li0.6[Li0.2Mn0.8]O2 lithium-rich material has a high reversible capacity due to the synergistic oxidation and reduction of anion and cation. However, the anion oxidation reaction that compensates the charge leads to a partial release of oxygen and the collapse of the structure inevitably. Here, we improve the structural stability of Li0.6[Li0.2Mn0.8]O2 by simultaneously introducing Al ions and B ions. Al ions and B ions randomly occupy octahedral and tetrahedral positions, hindering the migration of Mn ions and expanding the unit cell, resulting in a stable structure and promoting Li+ migration. The co-doped sample has better electrochemical performance than the bare material, and the capacity retention increases from 62.48% to 82.48% after 80 cycles at 0.1C rate, and still provides a capacity of 226 mAh g−1 between 2 and 4.8 V.  相似文献   

12.
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   

13.
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   

14.
LiCo2/3Ni1/6Mn1/6O2 layered oxide was synthesized by the combustion method that led to a crystalline phase with good homogeneity and low particles size. The structural properties of the prepared positive electrode material were investigated by performing XRD Rietveld refinement. Practically no Li/Ni mixing was detected evidencing that the studied compound adopts almost an ideal α-NaFeO2 type structure. The Li||LiCo2/3Ni1/6Mn1/6O2 cell showed a discharge capacity of 199 mAh g−1 when cycled in the 2.7–4.6 V potential range while the best cycling performances were recorded when the upper cut off is fixed at 4.5 V. Structural changes in LixCo2/3Ni1/6Mn1/6O2 with lithium electrochemical de-intercalation were studied using X-ray diffraction. This study clearly shows the existence of a solid solution domain in the 0.1 < x < 1.0 composition range while for x = 0.1, a new phase appears explaining the decrease of the electrochemical performance when the cell is cycled at high upper cut off voltage.  相似文献   

15.
In order to afford a possible way to avoid manganese dissolution during Li+ extraction/insertion of spinel-type LiMn2O4, the elution properties of HCl, (NH4)2S2O8, and Na2S2O8 were studied and the adsorption performance of Li+-extracted samples was characterized in Li+-containing solution. The results showed that Li+ was extracted by two different pathways: with manganese loss and without manganese loss. In the Li+ extraction process with manganese loss, ionic sieve was obtained after extracting Li+ from its precursor LiMn2O4, with accompanying partial transformation of Mn3+ to Mn4+ and Mn2+ by disproportionation reaction. This change caused the destruction of the framework and weight loss of ionic sieve due to the dissolution of Mn2+ in the solution. In the Li+ extraction process without manganese loss, Li+ was extracted with the reaction that part of Mn3+ was oxidized to Mn4+ by S2O82-. The Li+-extracted sample contained a small number of H+ which should exchange Li+ during this type of elution. The two Li+ extraction pathways also indicated that Li+ could not be completely eluted from the ionic sieve precursor. The uptake of Li+ on the ionic sieve was incomplete.  相似文献   

16.
The stress changes Δσ generated during lithium transport through the sol-gel derived LixMn2O4 film electrodes annealed at 773 and 873 K were quantitatively determined as a function of the lithium stoichiometry x using a laser beam deflection method (LBDM). Δσ generated during a real potential step between an initial electrode potential and a final applied potential was uniquely specified by the Δσ versus x curve. The LixMn2O4 film annealed at 773 K for 24 h (low temperature (LT)-LixMn2O4) showed larger capacity than the LixMn2O4 film annealed at 873 K for 6 h (high temperature (HT)-LixMn2O4) and this result is ascribed to the fact that the smaller the grain size is, the more increases the electrochemically active area of the film electrode. From the analysis of the normalised Δσ transient measured simultaneously along with the cyclic voltammogram in the potential range of 2.5-3.4 VLi/Li+, it is found that normalised Δσ generated in the LT-LixMn2O4 was smaller than that in the HT-LixMn2O4 during the lithium intercalation/de-intercalation around 3.0 VLi/Li+ region. This result gives an experimental evidence for the fact that the Jahn-Teller distortion is suppressed by the increase in the average oxidation state of manganese with decreasing in annealing temperature.  相似文献   

17.
《Ceramics International》2016,42(16):18620-18630
The development of Li-rich layer cathode materials has been limited by poor cycle, rate performance, phase transformation and voltage decay. To improve these properties, a facile and low-cost wet method is employed to fabricate Pr6O11 coating layer on Li[Li0.2Mn0.54Co0.13Ni0.13]O2 nanoparticles. The 3–6 nm Pr6O11 coating layer is observed on the surface of Li[Li0.2Mn0.54Co0.13Ni0.13]O2 by HRTEM. Interestingly, HAADF-STEM and EDS analyses show that the transition metal ions and the praseodymium ions mutually infiltrate in the Pr6O11 coating layer and Li[Li0.2Mn0.54Co0.13Ni0.13]O2 nanoparticles during calcination. A combination of HAADF-STEM with EDS and XPS studies reveals that Pr6O11 coating layer is bridged to Li[Li0.2Mn0.54Co0.13Ni0.13]O2 nanoparticles by the chemical bonds of transition phase Li1.2MXPr1−xO2. XRD patterns show that all samples are indexed to the layered structure α-NaFeO2, but the lattice parameters are influenced lightly after Pr6O11 coating. HRTEM and SAED analyses elucidate that the super large Pr ions surface-doping and the Pr6O11 coating are verified to suppress the transformation of layer to spinel structure in the bulk nanoparticles after cycles. The sample coated with 3 wt% Pr6O11 exhibits wonderful electrochemical performance with the first coulomb efficiency of 85.6%, the capacity retention ratio of 97.9% after 50 cycles and the discharge capacity of 162.2 mAh g−1 at 5 C. The resistant of charge transfer and the electrodes polarization are reduced by Pr6O11 coating according to EIS. Therefore, Pr6O11, which contains the super large Pr ions, plays two roles: the first one, it is coated on the Li[Li0.2Mn0.54Co0.13Ni0.13]O2 nanoparticles to optimize the environment of the interface reaction between electrodes and electrolyte; the other one, its Pr ions surface-doping stabilizes the structure in the superficial region of Li[Li0.2Mn0.54Co0.13Ni0.13]O2 nanoparticles and suppresses the voltage decay. The multifunctional Pr6O11 can play a significant role in accelerating development of new materials with excellent stabilization and high capacity.  相似文献   

18.
Relatively low capacity is a technological bottleneck of the development of sodium ion batteries. Herein, we present a series of hybrid layered cathode materials NaxLi1.5-xNi0.167Co0.167Mn0.67O2 (x?=?0.5, 0.6, 0.7, 0.8, 0.9, 1) with composite crystalline structures, which are prepared by co-precipitation method. The combined analysis of XRD, SEM and TEM reveals that the materials are composed of P2 structure, α-NaFeO2 structure and small amount of Li2MnO3. Among the as-prepared materials, Na0.6Li0.9Ni0.167Co0.167Mn0.67O2 delivers an initial reversible capacity of 222?mA?h?g?1 at 20?mA?g?1. Even at 100?mA?g?1, it shows a remarkable discharge capacity of 125?mA?h?g?1 in the first cycle and remains 60?mA?h?g?1 after 300 cycles. Such high capacity is achieved by the specific composite structure and sodium ions are proved to be able to intercalate/deintercalate in Li1.5Ni0.167Co0.167Mn0.67O2 with α-NaFeO2 structure. The Ex-situ XRD results of Na0.6Li0.9Ni0.167Co0.167Mn0.67O2 in the first cycle show that the P2 structure is well maintained along with irreversible phase transition of α-NaFeO2 structure, which is responsible for the long-term capacity fading. Owing to the high discharge capacity, the novel hybrid layered oxides NaxLi1.5-xNi0.167Co0.167Mn0.67O2 with composite structures can be considered as promising cathode materials to promote progress toward sodium-ion batteries.  相似文献   

19.
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   

20.
Li[Co1−zAlz]O2 (0 ≤ z ≤ 0.5) samples were prepared by co-precipitation and solid-state methods. The lattice constants varied smoothly with z for the co-precipitated samples but deviated for the solid-state samples above z = 0.2. The solid-state method may not produce materials with a uniform cation distribution when the aluminum content is large or when the duration of heating is too brief. Non-stoichiometric Lix[Co0.9Al0.1]O2 samples were synthesized by the co-precipitation method at various nominal compositions x = Li/(Co + Al) = 0.95, 1.0, 1.1, 1.2, 1.3. XRD patterns of the Lix[Co0.9Al0.1]O2 samples suggest the solid solution limit is between Li/(Co + Al) = 1.1 and 1.2. Electrochemical studies of the Li[Co1−zAlz]O2 samples were used to measure the rate of capacity reduction with Al content, found to be about −250 ± 30 (mAh/g)/(z = 1). Literature work on Li[Ni1/3Mn1/3Co1/3−zAlz]O2, Li[Ni1−zAlz]O2 and Li[Mn2−yAly]O4 demonstrates the same rate of capacity reduction with Al/(Al + M) ratio. These studies serve as baseline characterization of samples to be used to determine the impact of Al content on the thermal stability of delithiated Li[Co1−zAlz]O2 in electrolyte.  相似文献   

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