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1.
<正>Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4-δ are investigated using densityfunctional theory calculations.Results indicate that nonstoichiometric LiNi0.5Mn1.5O4-δ and stoichiometric LiNi0.5Mn1.5O4 exhibit two different structures,i.e.,the face-centred cubic(Fd-3m) and primitive,or simple,cubic (P4332) space groups,respectively.It is found that the magnetic ground state of LiNi0.5Mn1.5O4(P4332 and Fd-3m) is a ferrimagnetic state in which the Ni and Mn sublattices are ferromagnetically ordered along the[110]direction whereas they are antiferromagnetic with respect to each other.We demonstrate that it is the presence of an O-vacancy in LiNi0.5Mn1.5O4-δ with the Fd-3m space group that results in its superior electronic conductivity compared with LiNi0.5Mn1.5O4 with the P4332 space group.  相似文献   

2.
The cycling performances of LiNi0.5Mn1.5O4 (LNMO) were investigated and the reasons of capacity fading were discussed. The results show that LNMO can deliver about 115 mAh?g?1 at 1C at different temperatures; however, it retains only 61.57 % of its initial capacity after 130th cycles at 60 °C, which is much lower than 94.46 % of LNMO at 25 °C, and the cycling performance at 1C is better than that at 0.5C. The reason of capacity fading of LNMO at 60 °C is mainly due to the lower decomposition voltage of 4.3 V with commercial electrolyte and the larger decomposition current, of which the electrolyte decomposes and interacts with active materials to lead to the larger irreversible capacity loss. While the worse cycling performance at low rate is attributed to the longer interaction time between the electrolyte with the decomposition voltage of 4.5 V and the active materials.  相似文献   

3.
Li1.1Ni0.25Mn0.75O2.3 and Li1.5Ni0.25Mn0.75O2.5 have been synthesized by co-precipitation method. The effect of the LiNi0.5Mn1.5O4 spinel structure on physical and electrochemical properties is discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and electrochemical performance tests. The LiNi0.5Mn1.5O4 spinel structure is detected in the XRD pattern, TEM image, first discharge, and CV curves of the Li1.1Ni0.25Mn0.75O2.3 electrode. The rate, cyclic performance, and first coulomb efficiency of Li1.1Ni0.25Mn0.75O2.35 are higher than those of Li1.5Ni0.25Mn0.75O2.5. The first coulomb efficiencies of Li1.1Ni0.25Mn0.75O2.3 and Li1.5Ni0.25Mn0.75O2.5 are 86.2 and 74.7 %, and the capacity retentions are 98.7 and 94.1 % after 50 cycles, respectively. EIS results indicate that the charge-transfer reaction resistance of Li1.1Ni0.25Mn0.75O2.3 is lower than that of Li1.5Ni0.25Mn0.75O2.5, which is responsible for the better rate capacity of Li1.1Ni0.25Mn0.75O2.3.  相似文献   

4.
LiNi0.5Mn1.5O4 was synthesized as a cathode material for Li-ion batteries by a sonochemical reaction followed by annealing, and was characterized by XRD, SEM, HRTEM and Raman spectroscopy in conjunction with electrochemical measurements. Two samples were prepared by a sonochemical process, one without using glucose (sample-S1) and another with glucose (sample-S2). An initial discharge specific capacity of 130 mA h g−1 is obtained for LiNi0.5Mn1.5O4 at a relatively slow rate of C/10 in galvanostatic charge–discharge cycling. The capacity retention upon 50 cycles at this rate was around 95.4% and 98.9% for sample-S1 and sample-S2, respectively, at 30 °C.  相似文献   

5.
采用共沉淀法制备了LiNi0.5Mn0.5O2.XRD,Raman测试都表明材料是六方结构.XPS检测得出镍主要以正二价存在,锰元素主要以正四价存在.合成的LiNi0.5Mn0.5O2得到了50次的循环,但比容量较低.充放电循环性能比较研究表明,经过40次循环后,0.3,0.6,1.5 C的放电比容量分别是65.88,61.56,52.23 mA.h.g-1.  相似文献   

6.
M.W. Raja  S. Mahanty  R.N. Basu 《Solid State Ionics》2009,180(23-25):1261-1266
LiMn2O4 and LiNi0.5Mn1.5O4 powders have been synthesized by a novel cost-effective carbon exo-templating process. It has been observed that controlled nucleation in the pores of highly surface active carbon produces a distinct effect on the powder morphology and crystallinity. Quantitative X-ray phase analyses show single phase spinel structure having Fd3m symmetry for both samples. Field emission electron microscopy reveals particles of size 0.5–1.0 µm with well defined multi-faceted crystals. Cyclic voltammetry results show well separated distinct redox peaks at 4.05/3.92 and 4.17/4.08 V for LiMn2O4/Li and 4.91/4.61 V for LiNi0.5Mn1.5O4/Li coin cells indicating good crystallinity and reversibility of the cathodes compared to that of pristine LiMn2O4 synthesized by conventional combustion process. The LiMn2O4/Li and LiNi0.5Mn1.5O4/Li cells deliver an initial discharge capacity of 110 mA h/g and 122 mA h/g respectively at a current density of 0.05 mA/cm2 and when cycled at 0.2 mA/cm2, the cells maintain 81% and 96% of their initial discharge capacity respectively even after 20 cycles. On the other hand, at the same current density, LiMn2O4 synthesized by conventional combustion process suffers from severe capacity fading (only 37.5% capacity retention after the 25th cycle). The capacity fading rate is found to be very less even at further higher current densities (0.4–0.8 mA/cm2) for both LiMn2O4/Li and LiNi0.5Mn1.5O4/Li cells synthesized by the templating process. The present study reveals that high crystallinity along with multi-faceted morphology shows a remarkable enhancement in capacity as well as rate performance of pristine LiMn2O4 and its Ni derivative.  相似文献   

7.
We present the synthesis, characterization, and electrode behavior of LiNi0.5Mn1.5O4 spinels prepared by the wet-chemical method via citrate precursors. The phase evolution was studied as a function of nickel substitution and upon intercalation and deintercalation of Li ions. Characterization methods include X-ray diffraction, SEM, Raman, Fourier transform infrared, superconducting quantum interference device, and electron spin resonance. The crystal chemistry of LiNi0.5Mn1.5O4 appears to be strongly dependent on the growth conditions. Both normal-like cubic spinel [Fd3m space group (SG)] and ordered spinel (P4 1 32 SG) structures have been formed using different synthesis routes. Raman scattering and infrared features indicate that the vibrational mode frequencies and relative intensities of the bands are sensitive to the covalency of the (Ni, Mn)-O bonds. Scanning electron microscopy (SEM) micrographs show that the particle size of the LiNi0.5Mn1.5O4 powders ranges in the submicronic domain with a narrow grain-size distribution. The substitution of the 3d8 metal for Mn in LiNi0.5Mn1.5O4 oxides is beneficial for its charge–discharge cycling performance. For a cut-off voltage of 3.5–4.9 V, the electrochemical capacity of the Li//LiNi0.5Mn1.5O4 cell is ca. 133 mAh/g during the first discharge. Differences and similarities between LiMn2O4 and LiNi0.5Mn1.5O4 oxides are discussed.  相似文献   

8.
LiNi0.5Mn1.5O4 (LMNO) has attracted considerable attention as a Li-ion battery cathode material, owing to its high discharge voltage of 4.7 V (vs. Li/Li+) and high energy density. However, the electronic conductivity of LMNO is low, resulting in a low discharge capacity at high current density. To overcome this limitation, we deposited Au nanoparticles (NPs), which have a high conductivity and chemical stability at high battery voltages, on carbon-coated LMNO (LMNO/C) using ultrasound irradiation. Consequently, Au NPs that are ∼16 nm in size were deposited on LMNO/C, and ultrasound irradiation was reported to disperse the NPs on LMNO/C more effectively than stirring. Furthermore, the deposition of Au NPs on LMNO/C using ultrasound irradiation improved its electronic conductivity, which is related to an increase in the discharge capacity due to the reduction of Ni4+ to Ni2+ in LMNO/C at a high current density.  相似文献   

9.
Layered cathode Li1.5Ni0.25Mn0.75O2.5 has been synthesized and coated by Li4Ti5O12. The pristine and coated Li1.5Ni0.25Mn0.75O2.5 powders are characterized by X-ray diffraction (XRD), indicating the materials remained the layered structure before and after coating. The coated Li4Ti5O12 has been detected by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (DEX). The electrochemical performance, especially rate performance of Li1.5Ni0.25Mn0.75O2.5 electrode, is improved effectively after Li4Ti5O12 coating. The first discharge capacity, coulombic efficiency, and capacity retention of Li4Ti5O12-coated Li1.5Ni0.25Mn0.75O2.5 electrode are 244 mA h g?1, 81.5 %, and 98.3 % after 50 cycles, respectively. The Li4Ti5O12-coated Li1.5Ni0.25Mn0.75O2.5 electrode exhibits 108 mA h g?1 at 10 °C rate. Electrochemical impedance spectroscopy (EIS) results show that the charge transfer resistance (R ct) of Li1.5Ni0.25Mn0.75O2.5 electrode decreases after coating, which is due to the existence of Li4Ti5O12 with high lithium ion diffusion coefficient and suppression of the solid electrolyte interfacial (SEI) layer development and is responsible for the excellent rate capability and cyclic performance.  相似文献   

10.
Sun  Chun-Feng  Amruthnath  Nagdev  Yu  Jin-Shuai  Li  Wen-Jun 《Ionics》2016,22(8):1501-1508
Ionics - The pristine and Ru-doped LiNi0.5Mn0.5O2 cathode materials are synthesized by a wet chemical method, followed by a high-temperature calcination process. The influence of Ru substitution on...  相似文献   

11.
《Current Applied Physics》2019,19(4):440-446
A series of Mo doped Ni-Mn-Zn ferrites compounds with the formula Ni0.5Zn0.5Mn0.5-xMoxFe1.5O4 (x = 0, 0.025, 0.05, 0.075 and 0.1) were first synthesized by sol-gel auto-combustion method. The X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM) analysis were carried out to characterize the microstructural and magnetic properties of ferrites. Rietveld refinement of X-ray diffraction data confirmed the formation of cubic spinel structure and the emergence of FeMoO4 phase with the substitution of Mo6+ contents. The grain size increased remarkably due to the formation of the liquid phase. The saturation magnetization (Ms) increased while the coercivity (Hc) decreased from 67.3 to 12.1 Oe due to the decrease of magneto-crystalline anisotropy constant. The initial permeability (μi) increased significantly from 34 (x = 0) to 114 (x = 0.075) and later decreased for x = 0.1. In our experiment, Ni0.5Zn0.5Mn0.425Mo0.075Fe1.5O4 ferrite presented the best microstructure and soft magnetic properties.  相似文献   

12.
A cathode material, 0.5Li2MnO3 0.5LiNi0.5Mn0.5O2, was prepared by citric acid-assisted sol–gel method and its electrochemical performance was investigated. It delivered a charge capacity of 270 mAh g?1 and a discharge capacity of 189 mAh g?1 in the first cycle. With the increase of current density from 14 to 28 mA g?1, the discharge capacity dropped severely to 130 mA g?1. Obviously, the rate capability of the material was inferior to most of the oxide cathode materials. The diffusion coefficient of this material was calculated to be 6.04?×?10?12 cm2 s?1 from the results of cyclic voltammetry measurements. Moreover, diffusion coefficients between 3.13?×?10?12 and 1.22?×?10?10 cm2 s?1 in the voltage range of 3.8–4.7 V were obtained by capacity intermittent titration technique. This, together with the localized Li2MnO3 domains in the crystal structure, may validate the poor rate capability.  相似文献   

13.
The electrochemical performances of LiNi0.5Co0.2Mn0.3O2 (NCM523) layered cathode material, such as poor rate capacity and cycling stability caused by undesirable intrinsic conductivity and low rate of lithium ion transportation, are not fairly good especially at elevated rate and cut-off voltage. To improve these properties, in this study, the co-coating layer of graphene and TiO2 was constructed on NCM523 surface. The graphene/TiO2 coating layer could effectively prevent hydrofluoric acid (HF) attacks, suppress the side reaction, accelerate the lithium ion diffusion and facilitate the electron migration. The enhancement of cycle performance and rate capacity was contributed to the uniform co-modified surface, interacting each other and thus exhibiting synergistic effects.  相似文献   

14.
LiNi0.05Mn1.95O4 powders were prepared by manganese tetraoxide (MTO) and electrolytic manganese dioxide (EMD). The phase identification, surface morphology, and electrochemical properties of the prepared powders were studied by X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and galvanostatic charge?Cdischarge experiments. Compared to LiNi0.05Mn1.95O4 powders prepared by EMD, LiNi0.05Mn1.95O4 powders prepared by MTO show better crystallinity. Both powders possess a typical cubic structure with uniform particle size. The specific capacity and coulombic efficiency of LiNi0.05Mn1.95O4 powders prepared by MTO are higher than the one prepared by EMD. The capacity retention of LiNi0.05Mn1.95O4 powders prepared by MTO cycled 30 times at room temperature and 55?°C are 98.3% and 90.6%, respectively, which are much higher than those of 86.63% and 77.7% for the one prepared by EMD. LiNi0.05Mn1.95O4 powders prepared by MTO show higher specific capacity and better cycling performance than the one prepared by EMD.  相似文献   

15.
《Solid State Ionics》2006,177(1-2):113-119
LiNi0.4Mn1.6O4 was prepared under air and oxygen atmospheres using fine Mn3O4 particle and large MnO2 particle at various temperatures. The sample prepared from Mn3O4 at 750 °C under air or oxygen atmosphere exhibited an ideal electrochemical behavior, which was based on three redox couples of Mn3+/Mn4+, Ni2+/Ni3+, and Ni3+/Ni4+. On the other hand, the sample prepared from MnO2 had a larger capacity at 4 V plateau and smaller one at 5 V plateau. However, when using oxygen atmosphere, the sample exhibited more ideal behavior, which is similar to the sample prepared from Mn3O4. This means that some defects exist in LiNi0.4Mn1.6O4, depending on preparation conditions. In order to confirm this point, the chemical composition and the valence state of Mn of the prepared sample was analyzed. From these results, it can be said that electrochemical reactions of LiNi0.4Mn1.6O4 are well explained based on three redox couples of Mn3+/Mn4+, Ni2+/Ni3+, and Ni3+/Ni4+ by considering a presence of oxygen defects.  相似文献   

16.
Mn0.5Zn0.5Fe2O4 Magnetic nanofibers were fabricated by calcining electrospun polymer/inorganic composite nanofibers and characterized by thermogravimetric and differential thermal analysis, x-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy and a vibrating sample magnetometer. The experimental results show that the pure spinel structure is basically formed when the composite nanofibers are calcined at 450°C for 2h. With the increasing calcination temperature, both the saturation magnetization and coercivity of nanofiber samples increase initially along with the growth of Mn0.5Zn0.5Fe2O4 nanocrystals contained in the nanofibers. However, when the calcination temperature reaches 550°C, the saturation magnetization of nanofibers starts to dramatically decrease owing to the formation of the α-Fe2O3 phase at this temperature. The prepared Mn0.5Zn0.5Fe2O4 nanofibers calcined at 500°C for 2h have diameters ranging from 100 to 200nm. Their saturation magnetization and coercivity are 12.37emu/g and 4.81kA/m at room temperature, respectively.  相似文献   

17.
A LiNi0.6Co0.2Mn0.2O2/reduced graphene oxide (RGO) composite with RGO content of 1.2 % was prepared by a simple spray-drying method instead of high-energy ball milling method. The composite has been characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, energy dispersive spectroscopy, and charge/discharge test. The X-ray diffractometry result showed that composite possessed a typical hexagonal structure. The RGO sheets served as efficient electronically conductive frameworks benefitting from its 2D structure and outstanding electronic conductivity. The scanning electron microscope and transmission electron microscopy verified that LiNi0.6Co0.2Mn0.2O2 particles were wrapped with RGO sheets, which facilitated electronic conductivity between particles. The electrochemical results indicated that composite delivered a higher discharge capacity at various discharge rates. The cycling performance was also evaluated. The composite exhibited better cycling performance than pristine sample. Electrochemical impedance spectroscopy showed that the RGO can greatly reduce the charge transfer resistance. The results here gave clear evidence of RGO to improve electrochemical performance.  相似文献   

18.
l-Lysine was employed as additive to prepare face-centered cubic spinel Li4Mn5O12. During the process, l-lysine played important roles such as complexing agent as well as combusting agent and adjusting the pH values of solution. The physical characteristics of Li4Mn5O12 were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical capacitance performance of Li4Mn5O12 electrode was characterized by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. These analyses indicated that Li4Mn5O12 was able to deliver 168 F?g?1 within the potential range of 0–1.4 V at a scan rate of 5 mV?s?1 in 1 mol?L?1 Li2SO4. Nine hundred cycles later, the capacitance faded to 165 F?g?1 with cutting down by 0.003 F?g?1 per cycling period and also can remain 98.2 % of original value, displaying a good cycling performance.  相似文献   

19.
In this paper, we synthesize the MoO 3 modified LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode (denoted as M-NCM81) and compare with pristine LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode (denoted as P-NCM81). The M-NCM81 cathode delivers good cation ordering and typical spherical form. The M-NCM81 cathode shows initial discharge capacity of 203.8 mAh g −1 at 0.1 C, capacity retention of 79.8% under the 5.0 C. In addition, the M-NCM81 cathode still retain a discharge capacity of 172.2 mAh g −1after 100 cycles. Such electrochemical performances are significantly improved compared to those of P-NCM81. It can be elucidated that MoO 3 coating layer acts as a HF inhibitor/scavenger. The MoO 3 modification plays an important role in inhibiting severe structural degradation, derived from a harmful side reaction with electrolyte. It effectively suppresses the increase in charge-transfer resistance, leading to superior electrochemical performances.  相似文献   

20.
This paper reports on the first study of the magnetic properties of polycrystalline films of CoCr2O4 and CoFe0.5Cr1.5O4 multiferroics. The study covered, in particular, magnetization reversal curves and temperature dependences of the magnetization at temperatures ranging from 4.2 to 300 K in magnetic fields of up to 10 kOe. It has been shown that the Curie temperature and the pattern of the temperature dependence of the magnetization depend on the cation composition of the multiferroic. The temperature dependence of the magnetization of polycrystalline CoCr2O4 films has revealed an anomaly in the temperature range 10–70 K.  相似文献   

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