共查询到20条相似文献,搜索用时 15 毫秒
1.
Jun-Chao Zheng Xin-Hai LiZhi-Xing Wang Hua-Jun GuoQi-Yang Hu Wen-Jie Peng 《Journal of power sources》2009
The monoclinic-type Li3V2(PO4)3 cathode material was synthesized via calcining amorphous Li3V2(PO4)3 obtained by chemical reduction and lithiation of V2O5 using oxalic acid as reducer and lithium carbonate as lithium source in alcohol solution. The amorphous Li3V2(PO4)3 precursor was characterized by using TG–DSC and XPS. The results showed that the V5+ was reduced to V3+ by oxalic acid at ambient temperature and pressure. The prepared Li3V2(PO4)3 was characterized by XRD and SEM. The results indicated the Li3V2(PO4)3 powder had good crystallinity and mesoporous morphology with an average diameter of about 30 nm. The pure Li3V2(PO4)3 exhibits a stable discharge capacity of 130.08 mAh g−1 at 0.1 C (14 mA g−1). 相似文献
2.
Composites of monoclinic Li3−xM′xV2−yM″2y(PO4)3 (M′ = K, M″ = Sc, Mg + Ti) with carbon were synthesized by solid-state reaction using oxalic acid or 6% H2/Ar gas mixture as reducing agents at sintering temperature of 850 °C. The samples were characterized by X-ray diffraction (XRD), voltammetry and electrochemical galvanostatic cycling. The capacity of Li3V2(PO4)3 synthesized using hydrogen as the reducing agent was 127 mA h g−1 and decreased to 120 mA h g−1 after 20 charge-discharge cycles. The substitution of lithium and vanadium for other ions did not result in the improvement of the electrochemical characteristics of the samples. 相似文献
3.
Jun-chao Zheng Zhi-xing Wang De-rong Liu Ling-jun Li Hua-jun Guo 《Journal of power sources》2010,195(9):2935-2938
LiFePO4-Li3V2(PO4)3 composite cathode material is synthesized by aqueous precipitation of FeVO4·xH2O from Fe(NO3)3 and NH4VO3, following chemical reduction and lithiation with oxalic acid as the reducer and carbon source. Samples are characterized by XRD, SEM and TEM. XRD pattern of the compound synthesized at 700 °C indicates olivine-type LiFePO4 and monoclinic Li3V2(PO4)3 are co-existed. TEM image exhibits that LiFePO4-Li3V2(PO4)3 particles are encapsulated with a carbon shell 5-10 nm in thickness. The LiFePO4-Li3V2(PO4)3 compound cathode shows good electrochemical performance, and its discharge capacity is about 139.1 at 0.1 C, 135.5 at 1 C and 116 mA h g−1 at 3 C after 30 cycles. 相似文献
4.
Li1+x(Ni1/3Mn1/3Co1/3)1−xO2 layered materials were synthesized by the co-precipitation method with different Li/M molar ratios (M = Ni + Mn + Co). Elemental titration evaluated by inductively coupled plasma spectrometry (ICP), structural properties studied by X-ray diffraction (XRD), Rietveld analysis of XRD data, scanning electron microscopy (SEM) and magnetic measurements carried out by superconducting quantum interference devices (SQUID) showed the well-defined α-NaFeO2 structure with cationic distribution close to the nominal formula. The Li/Ni cation mixing on the 3b Wyckoff site of the interlayer space was consistent with the structural model [Li1−yNiy]3b[Lix+yNi(1−x)/3−yMn(1−x)/3Co(1−x)/3]3aO2 (x = 0.02, 0.04) and was very small. Both Rietveld refinements and magnetic measurements revealed a concentration of Ni2+-3b ions lower than 2%; moreover, for the optimized sample synthesized at Li/M = 1.10, only 1.43% of nickel ions were located into the Li sublattice. Electrochemical properties were investigated by galvanostatic charge-discharge cycling. Data obtained with Li1+x(Ni1/3Mn1/3Co1/3)1−xO2 reflected the high degree of sample optimization. An initial discharge capacity of 150 mAh g−1 was delivered at 1 C-rate in the cut-off voltage of 3.0-4.3 V. More than 95% of its initial capacity was retained after 30 cycles at 1 C-rate. Finally, it is demonstrated that a cation mixing below 2% is considered as the threshold for which the electrochemical performance does not change for Li1+x(Ni1/3Mn1/3Co1/3)1−xO2. 相似文献
5.
6.
Xiao-Jian Guo Yi-Xiao LiMin Zheng Jian-Ming ZhengJie Li Zheng-Liang GongYong Yang 《Journal of power sources》2008
A series of cathode materials with molecular notation of xLi[Li1/3Mn2/3]O2·(1 − x)Li[Ni1/3Mn1/3Co1/3]O2 (0 ≤ x ≤ 0.9) were synthesized by combination of co-precipitation and solid state calcination method. The prepared materials were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques, and their electrochemical performances were investigated. The results showed that sample 0.6Li[Li1/3Mn2/3]O2·0.4Li[Ni1/3Mn1/3Co1/3]O2 (x = 0.6) delivers the highest capacity and shows good capacity-retention, which delivers a capacity ∼250 mAh g−1 between 2.0 and 4.8 V at 18 mA g−1. 相似文献
7.
A series of Li deficient LiTi2(PO4)3 samples were prepared and sintered and the density was measured to determine the rate-controlling species for sintering of LiTi2(PO4)3. It was observed that as the Li content decreased the density decreased. This result suggests that oxygen does not control sintering. A comparison of the LiTi2(PO4)3 sintering data to sintering and diffusion data in olivine, which exhibits a similar framework structure to LiTi2(PO4)3, suggests that P is the species which controls sintering. This suggestion was confirmed by the density results of a Li excess LiTi2(PO4)3 sample. 相似文献
8.
A new type of Li1−xFe0.8Ni0.2O2–LixMnO2 (Mn/(Fe + Ni + Mn) = 0.8) material was synthesized at 350 °C in air atmosphere using a solid-state reaction. The material had an XRD pattern that closely resembled that of the original Li1−xFeO2–LixMnO2 (Mn/(Fe + Mn) = 0.8) with much reduced impurity peaks. The Li/Li1−xFe0.8Ni0.2O2–LixMnO2 cell showed a high initial discharge capacity above 192 mAh g−1, which was higher than that of the parent Li/Li1−xFeO2–LixMnO2 (186 mAh g−1). We expected that the increase of initial discharge capacity and the change of shape of discharge curve for the Li/Li1−xFe0.8Ni0.2O2–LixMnO2 cell is the result from the redox reaction from Ni2+ to Ni3+ during charge/discharge process. This cell exhibited not only a typical voltage plateau in the 2.8 V region, but also an excellent cycle retention rate (96%) up to 45 cycles. 相似文献
9.
Two iso-structural end members of the family of orthosilicates, i.e. Li2MSiO4 (M = Mn and Fe) and their solid solutions, were prepared and electrochemically characterized for potential use in Li-ion batteries. Due to the low specific conductivity (∼5 × 10−16 S cm−1 for Li2MnSiO4 and ∼6 × 10−14 S cm−1 for Li2FeSiO4 at room temperature), small particles in an intimate contact with a conducting phase (i.e. carbon) are needed. Li2MSiO4/C composites (M = Mn and/or Fe) prepared by the Pechini synthesis generally leads to 30–50 nm large particles embedded in a carbon matrix. The amount of carbon in the composite is close to 10 wt.% for the Li2FeSiO4/C composite and slightly more than 5 wt.% for the Li2MnSiO4/C composite. In situ XRD experiment confirms a structural collapse of Li2MnSiO4 and the observed structural stability is completely different for Li2FeSiO4, which undergoes a fully reversible two-phase transition. Solid solutions between Li2MnSiO4 and Li2FeSiO4 in principle lead to higher capacities (>1e− per transition metal is feasible). For a long-term operation the cut-off voltage should be properly chosen. Electrochemical characterisation and in situ XRD experiments suggest the use of cut-off voltage close to 4.2 V. 相似文献
10.
Deyu WangJie Xiao Wu XuZimin Nie Chongmin WangGordon Graff Ji-Guang Zhang 《Journal of power sources》2011,196(4):2241-2245
In this paper, we report the electrochemical characteristics of a novel cathode material, Li2CoPO4F, prepared by solid-state reactions. The solid-state reaction mechanism involved in synthesizing the Li2CoPO4F also is analyzed in this paper. When cycled between 2.0 V and 5.0 V during cyclic voltammetry measurements, the Li2CoPO4F samples present one, fully reversible anodic reaction at 4.81 V. When cycled between 2.0 V and 5.5 V, peaks occurring at 4.81 V and 5.12 V in the first anodic scan evolved to one broad oxidative, mound-like pattern in subsequent cycles. Correspondingly, the X-ray diffraction (XRD) pattern of the Li2CoPO4F electrode discharged from 5.5 V to 2.0 V is slightly different from the patterns exhibited by a fresh sample and the sample discharged from 5.0 V to 2.0 V. This difference may correspond to a structural relaxation that appears above 5 V. In the constant current cycling measurements, the Li2CoPO4F samples exhibited a capacity as high as 109 mAh g−1 and maintained a good cyclability between 2.0 V and 5.5 V vs. Li/Li+. XRD measurements confirmed that the discharged state is Li2CoPO4F. Combining these XRD results and electrochemical data proved that up to 1 mol Li+ is extractable when charged to 5.5 V. 相似文献
11.
Li Fang Jiao Ming ZhangHua Tang Yuan Ming ZhaoJian Guo Wei WangXing Di Zhou Yong Mei Wang 《Journal of power sources》2007
Prospective positive-electrode (cathode) materials for a lithium secondary battery, viz., Li[Li0.2Ni0.2−x/2Mn0.6−x/2Crx]O2 (x = 0, 0.02, 0.04, 0.06, 0.08), were synthesized using a solid-state pyrolysis method. The structural and electrochemical properties were examined by means of X-ray diffraction, cyclic voltammetry, SEM and charge–discharge tests. The results demonstrated that the powders maintain the α-NaFeO2-type layered structure regardless of the chromium content in the range x ≤ 0.08. The Cr doping of x = 0.04 showed improved capacity and rate capability comparing to undoped Li[Li0.2Ni0.2Mn0.6]O2. ac impedance measurement showed that Cr-doped electrode has the lower impedance value during cycling. It is considered that the higher capacity and superior rate capability of Cr-doping samples would be ascribed to the reduced resistance of the electrode during cycling. 相似文献
12.
Bulk conduction and relaxation of the [(ZrO2)1−x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions were studied using impedance spectroscopy at intermediate temperatures (200-500 °C). The bulk conductivity as a function of x shows a “V-shape” variation which is a competitive effect of the defect associates and the lattice parameter. In the ZrO2-rich region (x < 0.5) CeO2 doping increases the concentration of defect associates which limits the mobility of the oxygen vacancies; in the CeO2-rich region (x > 0.5) the increase of x increases the lattice parameter which enlarges the free channel for oxygen vacancy migration. Further analysis indicates the ionic radius of the tetravalent dopant determines the composition dependence of the ionic conductivity of the solid solutions. When doping YSZ with other tetravalent dopant with similar ionic radius with Zr4+, e.g., Hf4+, such “V-shape” composition dependence of the bulk conductivity cannot be observed. 相似文献
13.
A (Ni1/3Co1/3Mn1/3)CO3 precursor with an uniform, spherical morphology was prepared by coprecipitation using a continuously stirred tank reactor method. The as-prepared spherical (Ni1/3Co1/3Mn1/3)CO3 precursor served to produce dense, spherical Li1+x(Ni1/3Co1/3Mn1/3)1−xO2 (0 ≤ x ≤ 0.15) cathode materials. These Li-rich cathodes were also prepared by a second synthesis route that involved the use of an M3O4 (M = Ni1/3Co1/3Mn1/3) spinel compound, itself obtained from the carbonate (Ni1/3Co1/3Mn1/3)CO3 precursor. In both cases, the final Li1+x(Ni1/3Co1/3Mn1/3)1−xO2 products were highly uniform, having a narrow particle size distribution (10-μm average particle size) as a result of the homogeneity and spherical morphology of the starting mixed-metal carbonate precursor. The rate capability of the Li1+x(Ni1/3Co1/3Mn1/3)1−xO2 electrode materials, which was significantly improved with increased lithium content, was found to be better in the case of the denser materials made from the spinel precursor compound. This result suggests that spherical morphology, high density, and increased lithium content were key factors in enabling the high rate capabilities, and hence the power performances, of the Li-rich Li1+x(Ni1/3Co1/3Mn1/3)1−xO2 cathodes. 相似文献
14.
In order to search for cathode materials with better performance, Li3(V1−xMgx)2(PO4)3 (0, 0.04, 0.07, 0.10 and 0.13) is prepared via a carbothermal reduction (CTR) process with LiOH·H2O, V2O5, Mg(CH3COO)2·4H2O, NH4H2PO4, and sucrose as raw materials and investigated by X-ray diffraction (XRD), scanning electron microscopic (SEM) and electrochemical impedance spectrum (EIS). XRD shows that Li3(V1−xMgx)2(PO4)3 (x = 0.04, 0.07, 0.10 and 0.13) has the same monoclinic structure as undoped Li3V2(PO4)3 while the particle size of Li3(V1−xMgx)2(PO4)3 is smaller than that of Li3V2(PO4)3 according to SEM images. EIS reveals that the charge transfer resistance of as-prepared materials is reduced and its reversibility is enhanced proved by the cyclic votammograms. The Mg2+-doped Li3V2(PO4)3 has a better high rate discharge performance. At a discharge rate of 20 C, the discharge capacity of Li3(V0.9Mg0.1)2(PO4)3 is 107 mAh g−1 and the capacity retention is 98% after 80 cycles. Li3(V0.9Mg0.1)2(PO4)3//graphite full cells (085580-type) have good discharge performance and the modified cathode material has very good compatibility with graphite. 相似文献
15.
To prepare a high-capacity cathode material with improved electrochemical performance for lithium rechargeable batteries, Co3(PO4)2 nanoparticles are coated on the surface of powdered Li[Co0.1Ni0.15Li0.2Mn0.55]O2, which is synthesized by a simple combustion method. The coated powder prepared under proper conditions for Co3(PO4)2 content and annealing temperature shows an optimum coating layer that consists of a LixCoPO4 phase formed by reaction with lithium impurities during heat treatment. A sample coated with 3 wt.% Co3(PO4)2 and annealed at 800 °C proves to be the best in terms of specific capacity, cycle performance and rate capability. Thermal stability is also enhanced by the coating, as demonstrated a decrease in the onset temperature and/or the heat generated during thermal runaway. 相似文献
16.
Ji-Hwa JeongBong-Soo Jin Woo-Seong KimGuoxiu Wang Hyun-Soo Kim 《Journal of power sources》2011,196(7):3439-3442
Cathode materials prepared by a co-precipitation are 0.3Li2MnO3·0.7LiMn1−xNiyCo0.1O2 (0.2 ≤ x ≤ 0.4) cathode materials with a layered-spinel structure. In the voltage range of 2.0-4.6 V, the cathodes show more than one redox reaction peak during its cyclic voltammogram. The Li/0.3Li2MnO3·0.7LiMn1−xNiyCo0.1O2 (x = 0.3, y = 0.2) cell shows the initial discharge capacity of about 200 mAh g−1. However, when x = 0.2 and y = 0.1, the cell exhibits a rapid decrease in discharge capacity and poor cycle life. 相似文献
17.
Effect of CO2 on layered Li1+zNi1−x−yCoxMyO2 (M = Al,Mn) cathode materials for lithium ion batteries
We investigated the effect of CO2 on layered Li1+zNi1−x−yCoxMyO2 (M = Al, Mn) cathode materials for lithium ion batteries which were prepared by solid-state reactions. Li1+zNi(1−x)/2CoxMn(1−x)/2O2 (Ni/Mn mole ratio = 1) singularly exhibited high storage stability. On the other hand, Li1+zNi0.80Co0.15Al0.05O2 samples were very unstable due to CO2 absorption. XPS and XRD measurements showed the reduction of Ni3+ to Ni2+ and the formation of Li2CO3 for Li1+zNi0.80Co0.15Al0.05O2 samples after CO2 exposure. SEM images also indicated that the surfaces of CO2-treated samples were covered with passivation films, which may contain Li2CO3. The relationship between CO2-exposure time and CO32− content suggests that there are two steps in the carbonation reactions; the first step occurs with the excess Li components, Li2O for example, and the second with LiNi0.80Co0.15Al0.05O2 itself. It is well consistent with the fact that the discharge capacity was not decreased and the capacity retention was improved until the excess lithium is consumed and then fast deterioration occurred. 相似文献
18.
R. Dominko C. Vidal-Abraca GarridoM. Bele M. KuezmaI. Arcon M. Gaberscek 《Journal of power sources》2011,196(16):6856-6862
Li2−xVTiO4/C sample with a disordered rock salt structure was successfully prepared by annealing at a temperature of 850 °C. The electrochemical oxidation in the first cycle occurs at voltages above 4 V vs. metallic lithium, while the shapes of the electrochemical curves in consequent reduction-oxidation processes show a monotonous change of the potential between the selected cut-off voltages. A linear combination fit of individual XANES spectra was used for the determination of the oxidation states of as prepared sample and intermediate states during oxidation and reduction. In the as-prepared sample, vanadium was found to be in the average oxidation state of V3.5+ and was additionally oxidized to V3.8+ by the electrochemical charging. During the discharge process, the vanadium oxidation state was reduced to V3.0+. In situ X-ray diffraction patterns and EXAFS analysis suggest good structural stability during oxidation and reduction, which is also reflected in the cycling stability if batteries were cycled in the voltage window between 2.0 V and 4.4 V. Extension of the lower cut-off voltage to 1.0 V doubles the capacity retention with the improved capacity stability if compared with several high capacity vanadium based materials. 相似文献
19.
A two-dimensional sample array synthesis has been used to screen carbon-coated Li(1−x)Mgx/2FePO4 and LiFe(1−y)MgyPO4 powders as potential positive electrode materials in lithium ion batteries with respect to x, y and carbon content. The synthesis route, using sucrose as a carbon source as well as a viscosity-enhancing additive, allowed introduction of the Mg dopant from solution into the sol–gel pyrolysis precursor. High-throughput XRD and cyclic voltammetry confirmed the formation of the olivine phase and percolation of the electronic conduction path at sucrose to phosphate ratios between 0.15 and 0.20. Measurements of the charge passed per discharge cycle showed that the capacity deteriorated on increasing magnesium in Li(1−x)Mgx/2FePO4, but improved with increasing magnesium in LiFe(1−y) MgyPO4, especially at high scan rates. Rietveld-refined XRD results on samples of LiFe(1−y)MgyPO4 prepared by a solid-state route showed a single phase up to y = 0.1 according to progressive increases in unit cell volume with increases in y. Carbon-free samples of the same materials showed conductivity increases from 10−10 to 10−8 S cm−1 and a decrease of activation energy from 0.62 to 0.51 eV. Galvanostatic cycling showed near theoretical capacity for y = 0.1 compared with only 80% capacity for undoped material under the same conditions. 相似文献
20.
In this work structural and transport properties of layered Li1+x(Mn1/3Co1/3Ni1/3)1−xO2 oxides (x = 0; 0.03; 0.06) prepared by a “soft chemistry” method are presented. The excessive lithium was found to significantly improve transport properties of the materials, a corresponding linear decrease of the unit cell parameters was observed. The electrical conductivity of Li1.03(Mn1/3Co1/3Ni1/3)0.97O2 composition was high enough to use this material in a form of a pellet, without any additives, in lithium batteries and characterize structural and transport properties of deintercalated Li1.03−y(Mn1/3Co1/3Ni1/3)0.97O2 compounds. For deintercalated samples a linear increase of the lattice parameter c together with a linear decrease of the parameter a with the increasing deintercalation degree occurred, but only up to 0.4-0.5 mol of extracted lithium. Further deintercalation showed a reversal of the trend. Electrical conductivity measurements performed of Li1.03−y(Mn1/3Co1/3Ni1/3)0.97O2 samples (y = 0.1; 0.3; 0.5; 0.6) showed an ongoing improvement, almost two orders of magnitude, in relation to the starting composition. Additionally, OCV measurements, discharge characteristics and lithium diffusion coefficient measurements were performed for Li/Li+/Li1.03−y(Mn1/3Co1/3Ni1/3)0.97O2 cells. 相似文献