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1.
By employment of nano-sized pre-prepared Mn3O4 as precursor, LiMn2O4 particles have been successfully prepared by facile solid state method and sol-gel route, respectively. And the reaction mechanism of the used precursors of Mn3O4 is studied. The structure, morphology, and element distribution of the as-synthesized LiMn2O4 samples are characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Compared with LiMn2O4 synthesized by facile solid state method (SS-LMO), LiMn2O4 synthesized by modified sol-gel route (SG-LMO) possesses higher crystallinity, smaller average particle size (~175 nm), higher lithium chemical diffusion coefficient (1.17 × 10?11 cm2 s?1), as well as superior electrochemical performance. For example, the cell based on SG-LMO can deliver a capacity of 85.5 mAh g?1 at a high rate of 5 °C, and manifests 88.3% capacity retention after 100 cycles at 0.5 °C when cycling at 45 °C. The good electrochemical performance of the cell based on SG-LMO is ascribed mainly to its small particle size, high degree of dispersion, and uniform element distribution in bulk material. In addition, the lower polarization potential accelerates Li+ ion migration, and the lower atom location confused degree maintains integrity of crystal structure, both of which can effectively improve the rate capability and cyclability of SG-LMO.  相似文献   

2.
Pure LiMn2O4 samples with high crystallinity (LMO-1# and LMO-2#) were successfully synthesized by a facile hydrothermal method using δ-MnO2 nanoflowers and α-MnO2 nanowires as the precursors. The as-prepared samples were analyzed by XRD, SEM, and Brunauer-Emmett-Teller (BET), and their capacitive properties were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge test. Two LiMn2O4 samples showed good capacitive behavior in aqueous hybrid supercapacitors. AC//LMO-1# and AC//LMO-2# delivered the initial specific capacitance of 45.4 and 40.7 F g?1 in 1 M Li2SO4 electrolyte at a current density of 200 mA g?1 in the potential range of 0~1.5 V, respectively. After 1000 cycles, the capacitance retention was 97.6% for AC//LMO-1# and 93.7% for AC//LMO-2#. Obviously, LMO-1# from δ-MnO2 nanoflowers exhibited higher specific capacitance and better cycling performance than LMO-2#, so LMO-1# was more suitable as the positive electrode material in hybrid supercapacitors.  相似文献   

3.
Lithium manganese oxide (LiMn2O4) has been prepared using sol-gel technique under acidic (pH = 5.8) and alkaline (pH = 9) conditions with tartaric acid as chelating agent. X-ray studies show that under acidic condition, an Mn2O3 peak was observed indicating the presence of impurities. No impurity was observed for LiMn2O4 under alkaline conditions. The particle size is mostly in the range of 124 to 185 nm from HR-TEM. The lithium diffusion coefficient, D Li+ in LiMn2O4 is of the order 10?9 cm2 s?1. By using density functional theory (DFT) calculations, structural properties have been obtained. The specific discharge capacity of the cells with LiMn2O4 prepared under alkaline condition and with LiMn2O4 prepared under acidic condition discharged at 0.5 C is in the ranges of 132 to 142 and 128 to 139 mAh g?1, respectively.  相似文献   

4.
A simple one-step solid state reaction way of preparing nanosized LiMn2O4 powders with high-rate properties is investigated. Oxalic acid is used as a functional material to lose volatile gases during the process of calcining in order to control the morphology and change the particle size of materials. The results of X-ray diffraction and scanning electron microscopy show that particle size of materials decreases with the increase of the oxalic acid content. The electrochemical test results indicate that optimal LiMn2O4 particles (S0.5) is synthesized when the molar ratios of oxalic acid and total Mn source are 0.5:1. It also manifests that LiMn2O4 sample with middle size has the optimal electrochemical performance among five samples instead of the smallest LiMn2O4 sample. The obtained sample S0.5 with middle size exhibits a high initial discharge capacity of 125.8 mAh g?1 at 0.2C and 91.4% capacity retention over 100 cycles at 0.5C, superior to any one of other samples. In addition, when cycling at the high rate of 10C, the optimal S0.5 in this work could still reach a discharge capacity of 80.8 mAh g?1. This observation can be addressed to the fact that the middle size particles balance the contradictory of diffusion length in solid phase and particle agglomeration, which leads to perfect contacts with the conductive additive, considerable apparent Li-ion diffusion rate, and the optimal performance of S0.5.  相似文献   

5.
ZnO-coated LiMn2O4 cathode materials were prepared by a combustion method using glucose as fuel. The phase structures, size of particles, morphology, and electrochemical performance of pristine and ZnO-coated LiMn2O4 powders are studied in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge test, and X-ray photoelectron spectroscopy (XPS). XRD patterns indicated that surface-modified ZnO have no obvious effect on the bulk structure of the LiMn2O4. TEM and XPS proved ZnO formation on the surface of the LiMn2O4 particles. Galvanostatic charge/discharge test and rate performance showed that the ZnO coating could improve the capacity and cycling performance of LiMn2O4. The 2 wt% ZnO-coated LiMn2O4 sample exhibited an initial discharge capacity of 112.8 mAh g?1 with a capacity retention of 84.1 % after 500 cycles at 0.5 C. Besides, a good rate capability at different current densities from 0.5 to 5.0 C can be acquired. CV and EIS measurements showed that the ZnO coating effectively reduced the impacts of polarization and charge transfer resistance upon cycling.  相似文献   

6.
In order to overcome the severe capacity decay of LiMn2O4 at high temperature, TiN is used as an active materials additive in this paper. The XRD and XPS test results indicate that the TiN can effectively prevent Mn from dissolving in electrolyte; galvanostatic charge-discharge test shows that LiMn2O4 electrode with TiN exhibits remarkably improved capacity retention at high temperature with capacity of 105.1 mAh g?1 at 1 C in the first cycle at 55 °C and the capacity maintains 88.9% retention after 150 cycles. And the electrochemical impedance spectroscopy result demonstrates TiN’s effectiveness in easing the increase of charge-transfer resistance during cycling. Therefore, we can conclude that TiN, as an addictive, made obvious contribution to the greatly improved electrochemical cycling performance of LiMn2O4.  相似文献   

7.
Antimony trioxide (Sb2O3) nanoparticles with particle size range from 2 to 12 nm were successfully synthesized by chemical reducing method. Antimony trichloride was reduced by hydrazine with the presence of sodium hydroxide (NaOH) as catalyst in ethylene glycol at 120 °C for 1 h. Effects of hydrazine concentration ([N2H5OH]/[Sb3+] = 0.75, 5, 10, 20, and 30, when concentration of NaOH was fixed [NaOH]/[Sb3+] = 3) and NaOH concentration ([NaOH]/[Sb3+] = 0, 1, 3, and 5, when concentration of hydrazine was fixed [N2H5OH]/[Sb3+] = 10) on the particle size and shape of the Sb2O3 nanoparticles were investigated. Transmission electron microscope, selected area electron diffraction pattern, and high resolution electron microscope were employed to study the morphology and crystallinity of the nanoparticles. It was observed that the particle size decreased and remained constant when [N2H5OH]/[Sb3+]) ≥ 10 and [NaOH]/[Sb3+] = 3. Further study on the crystallinity and phase of the nanoparticles was assisted by X-ray diffractometer (XRD). XRD revealed a cubic phase of Sb2O3 (ICDD file no. 00-043-1071) with preferred plane of (622) and lattice spacing of 1.68 Å. Correlation between UV–visible absorption wavelengths of the nanoparticles and their sizes was established.  相似文献   

8.
A novel facile approach to coat LiMn2O4 by lithium polyacrylate (PAALi) is demonstrated. The PAALi-coated LiMn2O4 (LMO@2%PAALi) and LiMn2O4 (LMO) are characterized by charge–discharge tests, X-ray diffraction (XRD), PAALi dissolving experiment, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), and inductively coupled plasma optical emission spectrometer (ICP-OES). XRD and FTIR analyses indicate that there are no clear differences between LMO@2%PAALi and LMO. PAALi dissolving experiment indicates that PAALi is indissolvable in LiPF6-EC/DMC/EMC electrolyte. TEM results reveal that LiMn2O4 particles are coated by PAALi. ICP-OES results indicate that this stable PAALi coating can prevent the Mn ions dissolving from active LiMn2O4 materials and then the stability of LiMn2O4 crystals in electrolyte are greatly enhanced. These unique features ensure that LMO@2%PAALi possesses much better rate performance, higher discharge capacity, better cycling performance, and lower charge transfer resistance over LMO. The discharge capacity of LMO@2%PAALi at 0.2 C reaches up to 127.2 mAh g?1 at room temperature.  相似文献   

9.
A series of Li3V2(PO4)3/C composite cathodes have been prepared by the organic solvent replacement drying method. Five kinds of organic solvent including ethyl alcohol, butyl alcohol, 2-methoxyethanol, 1,2-propylene glycol, and ethylene glycol were used in the drying process to replace the water respectively. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge tests were employed to analyze the crystal structure, morphology, and electrochemical properties of the as-prepared materials. The results show that the organic solvent has a great influence on the secondary particle size of the as-synthesized materials. Special emphasis is placed on the sample prepared with 1,2-propylene glycol, which has the smallest average particle size and uniform distribution, thus leading to the best high rate performance and long-term cycling stability. The electrode exhibits average specific discharge capacities of 127.6, 128.3, 127.7, 126.7, 125.5, 124.4, 121.9, and 117.0 mAh g?1 at 0.1, 0.2, 0.5, 1, 3, 5, 10, and 20C, respectively. More encouragingly, this sample delivers an outstanding cycle life with capacity retention of up to 94.68% even after 1000 cycles at 20C. Moreover, EIS results demonstrate that this sample has the minimum resistance and the largest apparent lithium ion diffusion coefficient (1.569 × 10?7 cm2 s?1) which can facilitate to the Li+ diffusion during the charge/discharge process. Our results indicate that this preparation strategy can be facile and versatile for the synthesis of other high-rate and high-capacity intercalation materials.  相似文献   

10.
In this study, well-crystallized Li4Mn5O12 powder was synthesized by a self-propagating combustion method using citric acid as a reducing agent. Various conditions were studied in order to find the optimal conditions for the synthesis of pure Li4Mn5O12. The precursor obtained was then annealed at different temperatures for 24 h in a furnace. X-ray diffraction results showed that Li4Mn5O12 crystallite is stable at relatively low temperature of 400 °C but decompose to spinel LiMn2O4 and monoclinic Li2MnO3 at temperatures higher than 500 °C. The prepared samples were also characterized by FESEM and charge-discharge tests. The result showed that the specific capacity of 70.7 mAh/g was obtained within potential range of 4.2 to 2.5 V at constant current of 1.0 mA. The electrochemical performances of Li4Mn5O12 material was further discussed in this paper.  相似文献   

11.
Rare earth elements (RE = Eu3+& Dy3+)and Bi3+ doped Y2O3 nanoparticles were synthesized by urea hydrolysis method in ethylene glycol, which acts as reaction medium as well as a capping agent, at a low temperature of 140 °C,followed by calcination of the obtained product. Transmission electron microscope (TEM) images reveals that ovoid shaped Y2O3 nanoparticles of around 22–24 nm size range were obtained in this method. The respective RE and Bi3+ doped Y2O3 precursor nanoparticles when heated at 600 and 750 °C, retains the same shape as that of the as-synthesized Y2O3 precursor samples. From EDAX spectra, the incorporation of RE ions into the host has been studied. XRD pattern reveals the crystalline nature of the heated nanoparticles and indicate the absence of any impurity phase other than cubic Y2O3.However, the as-synthesized nanoparticles were highly amorphous without the presence of any sharp XRD peaks. Photoluminescence study suggests that the synthesized samples could be used as red (Eu3+), yellow (Dy3+), blue and green (Bi3+)emitting phosphors.  相似文献   

12.
Cathode material LiMn2O4 nanorod was prepared by annealing of the mixed precursor which was synthesized by low heating solid state coordination method using lithium acetate, manganese acetate and oxalic acid as starting materials. The structures and morphologies of the LiMn2O4 nanorod were investigated as a function of annealing temperature and time. The results showed that all samples in different annealing temperatures and time have the same spinel structure. The higher the annealing temperature is, the more complete the crystal structure forms, and the larger the particle size is. In addition, the electrochemical properties of the LiMn2O4nanorod were studied in this paper.  相似文献   

13.
Yan-Rong Zhu  Ting-Feng Yi 《Ionics》2016,22(10):1759-1774
High-voltage spinel LiNi0.5Mn1.5O4 has been considered one of the most promising cathode materials for lithium-ion power batteries used in electrical vehicles (EVs) or hybrid electrical vehicles (HEVs) because the high voltage plateau at around 4.7 V makes its energy density (658 Wh kg?1) 30 and 25 % higher than that of conventional pristine spinel LiMn2O4 (440 Wh kg?1) or olivine LiFePO4 (500 Wh kg?1) materials, respectively. Unfortunately, LiNi0.5Mn1.5O4-based batteries with LiPF6-based carbonate electrolytes always suffer from severe capacity deterioration and poor thermostability because of the oxidization of organic carbonate solvents and decomposition of LiPF6, especially at elevated temperatures and water-containing environment. The major goal of this review is to highlight the recent advancements in the development of advanced electrolytes for improving the cycling stability and rate capacity of LiNi0.5Mn1.5O4-based batteries. Finally, an insight into the future research and further development of advanced electrolytes for LiNi0.5Mn1.5O4-based batteries is discussed.  相似文献   

14.
This report discusses the preparation and microstructure of Co/Ni co-doped MgGa2O4 nanoparticles. The nanoparticles with the size of 20–55 nm were synthesized by sol-gel method. The phase and crystallinity were confirmed by X-ray powder diffraction (XRD) pattern. The particle size was estimated according to XRD data and transmission electron microscopy. The electronic structure was studied using X-ray photoelectron spectroscopy (XPS). The XPS studies showed that Ga3+ ions possess tetrahedral and octahedral sites of spinel structure and the inverse degree (two times of the fraction of tetrahedral Ga3+ ions) has increased with the increase of the doping concentration of Co2+ and Ni2+ ions. For Co/Ni co-doped MgGa2O4, two broad absorption bands of 350~500 and 550~700 nm were observed in the absorption spectra. The broad band at 350~500 nm was assigned to the combination of the absorption of octahedral Co2+ and Ni2+ ions, whereas the absorption band at 550~700 nm is mainly due to tetrahedrally coordinated Co2+ ions and octahedrally coordinated Ni2+ ions.  相似文献   

15.
LiNi0.5Co0.2Mn0.3O2 particles of uniform size were prepared through carbonate co-precipitation method with acacia gum. The precursor of carbonate mixture was calcined at 800 °C, and a well-crystallized Ni-rich layered oxide was got. The phase structure and morphology were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The micro-sized particles delivered high initial discharge capacity of 164.3 mA h g?1 at 0.5 C (1 C?=?200 mA g?1) between 2.5 and 4.3 V with capacity retention of 87.5 % after 100 cycles. High reversible discharge capacities of 172.4 and 131.4 mA h g?1 were obtained at current density of 0.1 and 5 C, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed to further study the LiNi0.5Co0.2Mn0.3O2 particles. Anyway, the excellent electrochemical performances of LiNi0.5Co0.2Mn0.3O2 sample should be attributed to the use of acacia gum.  相似文献   

16.
The hierarchical LiMn0.5Fe0.5PO4/C (LMFP) nanorods were first successfully synthesized by rheological phase method using polyethylene glycol 4000 (PEG 4000) as a template reagent. The physical and electrochemical properties of the LiMn0.5Fe0.5PO4/C were characterized by TG-DTG, XRD, FTIR, SEM, TEM, EIS and galvanostatic charge-discharge measurements. The results reveal that the PEG-LMFP/C synthesized with the assistance of PEG 4000 shows unique bundle-type shape assembled of nanorods, while the LMFP/C synthesized without PEG 4000 presents a platelet-like shape with some agglomeration. Besides, a uniformly carbon layer coating on the surface of the PEG-LMFP/C can be seen from TEM images. The PEG-LMFP/C exhibits high specific capacity and superior rate performance with discharge capacities of 162, 133, 108, 95, and 78 mAh?·?g?1 at 0.1, 1, 5, 10, and 20 C rates, respectively. It is demonstrated that the synthesis of LMFP/C with PEG 4000 can significantly decrease the characteristic sizes of the crystals, resulting in improved electrochemical performance.  相似文献   

17.
Nanoparticles of the pure and Ni–Cr co-doped lithium manganese oxides Li[NixCryMn2-x-y]O4 (x = y = 0.01–0.05) have been synthesized by sol–gel method using citric acid as a chelating agent. The effect of low-content doping was noted reflecting the faster ionic movement in the cathode material. The phase structure and morphology of the materials are characterized by XRD, FTIR, SEM and TEM. Electrochemical and impedance measurements established that low-content Ni–Cr substitution substantially improves the structural stability and high rate cycling performance of LiMn2O4. Among all the investigated compositions, LiNi0.01Cr0.01Mn1.98O4 demonstrated the best electrochemical performance. At a substantially high current rate of 5 C, 82% of the initial discharge capacity at 0.1 C is retained. Remarkably, after deep cycling at high rates, a discharge capacity of 104 mAhg?1 is resumed upon reducing the current rate to 0.1 C which is 91% of the specific capacity in the first cycle.  相似文献   

18.
The high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) with submicron particle size (LNMO-8505P70010) has been synthesized based on nickel-manganese compound, which is obtained from pre-sintering the nickel-manganese hydroxide precipitation at 850 °C. The LNMO materials based on nickel-manganese hydroxide (LNMO-70010, LNMO-850570010, and LNMO-8501070010) have also been synthesized for comparison to study the pre-sintering impact on the properties of LiNi0.5Mn1.5O4 material. The morphologies and structures of the obtained samples have been analyzed by X-ray powder diffraction and scanning electron microscopy. The nickel-manganese compound has a spinel structure with high crystallinity, making it a good precursor to form high-performance LNMO with lower content of Mn3+ and impurity. The obtained LNMO-8505P70010 delivers discharge capacities of 125.4 mA h g?1 at 0.2 C, and the capacity retention of 15 C reaches 73.8 % of the capacity retention of 0.2? C. Furthermore, it shows a superior cyclability with the capacity retention of 96.4 % after 150 cycles at 5 ?C. Compared with the synthesis method without pre-sintering, the synthesis method with pre-sintering can save energy while reaching the same discharge specific capacity.  相似文献   

19.
A novel approach of double hydroxide-mediated synthesis of nickel cobaltite (NiCo2O4) electro-active material by the hydrothermal method is reported. The obtained NiCo2O4 electro-active material displays the spinel cubic phase and hexagonal-like morphology. Thermogravimetry analysis confirms the thermal stability of the electrode material. The functional groups and phase formation of NiCo2O4 have been confirmed by FT-IR and Raman spectral analysis. The modified NiCo2O4 electrode exhibits the highest specific capacitance of 767.5 F g?1 at a current density of 0.5 A g?1 in 3 M KOH electrolyte and excellent cyclic stability (94 % capacitance retention after 1000 cycles at a high current density of 5 A g?1). The excellent electrochemical performance of the electrode is attributed to the hexagonal-like morphology, which contributes to the rich surface electro-active sites and easy transport pathway for the ions during the electrochemical reaction. The attractive Faradic behavior of NiCo2O4 electrode has been ascribed to the redox contribution of Ni2+/Ni3+ and Co2+/Co3+ metal species in the alkaline medium. The symmetrical two-electrode cell has been fabricated using the NiCo2O4 electro-active material with excellent electrochemical properties for supercapacitor applications.  相似文献   

20.
The lithiated transition metal oxide precursor (LNCMO) with typical α-NaFeO2 structure and imperfect crystallinity, obtained from a hydrothermal process, was pretreated at 500 °C and then subjected to sintering at 800–920 °C to synthesize the ternary layered LiNi0.5Co0.2Mn0.3O2 (NCM523). X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge testing were used for investigating the effect of the high-temperature crystallization on the properties of the NCM523 cathode materials. The results show that the materials heated at 880–900 °C possess superior cation ordering, perfect crystallinity, and excellent electrochemical performances, among which the material heated at 900 °C delivers better performances, with the initial discharge capacity of 152.6 mAh g?1 at 0.5 C over 3.0 to 4.3 V and the capacity retention of 95.5% after 50 cycles. Furthermore, the effect of the high-temperature crystallization on the Li+ diffusion coefficient, potential polarization, and electrochemical resistance are discussed.  相似文献   

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