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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.
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   

3.
Herein, we reported the synthesis of uniform LiMn2O4 submicroparticles by surfactant-assisted preparation of spherical MnCO3 precursor followed by solid-state reaction. Polyethylene glycol (Mw = 1000) was used as surfactant to control the morphology and size of the MnCO3 precursor as well as the MnO2 intermediate and LiMn2O4 product. The influence of particle size, homogeneity, and crystallinity on the electrochemical performance of LiMn2O4 was intensively investigated. The test results indicate that the LiMn2O4 sample using polyethylene glycol with weight as 10% of reactants shows the best rate capability and long-term cyclability. Due to the homogeneous particles with the average size of ca. 250 nm and high crystallinity, the discharge capacities are as high as 125, 118, 114, and 100 mAh g?1 at 1, 10, 20, and 50 C rates, respectively, along with high capacity retention of 74% after 1000 cycles at 20 C.  相似文献   

4.
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   

5.
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   

6.
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   

7.
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   

8.
Li2Mn4O9 and molybdenum-doped Li2Mn4O9 have been prepared by simple solid-state method. Molybdenum is used as a dopant since it is resistant to both corrosion and high-temperature creep deformation. The structural, morphological, and electrical performances of the samples have been analyzed. The material exhibits a cubic structure with the fd3m space group. Using EDAX, the chemical compositions of the samples have been identified. The dc electrical conductivity of the Mo-doped (LM2) sample is found to be increased to 7.44?×?10?6 S cm?1 at 393 K. The enhanced electrical property of the molybdenum-doped Li2Mn4O9 reveals it as a feasible cathode material for rechargeable Li-ion batteries.  相似文献   

9.
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   

10.
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   

11.
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   

12.
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   

13.
Carbon encapsulated Li4Ti5O12 (C/Li4Ti5O12) anode material for lithium ion battery was prepared by using the pre-coat method of two steps, and the TiO2 was pre coated before the reaction with Li2CO3. The structure and morphology of the resultant C/Li4Ti5O12 materials were characterized by X-ray diffraction (XRD) and scanning microscopy (SEM). Electrochemical tests showed that at 0.1 C, the initial discharge capacity was 169.9 mAh g?1, and the discharge capacity was 80 mAh g?1 at 5 C. After 100 cycles at 2 C, the discharge specific capacity was 108.5 mAh g?1. Compare with one step coating method, results showed the C/Li4Ti5O12 prepared by pre-coat method can reduce the particle’s size and effectively improve the electrochemical performance.  相似文献   

14.
A Co3O4/vapor-grown carbon fiber (VGCF) hybrid material is prepared by a facile approach, namely, via liquid-phase carbonate precipitation followed by thermal decomposition of the precipitate at 380 °C for 2 h in argon gas flow. The material is characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller specific surface area analysis, and carbon elemental analysis. The Co3O4 in the hybrid material exhibits the morphology of porous submicron secondary particles which are self assembled from enormous cubic-phase crystalline Co3O4 nanograins. The electrochemical performance of the hybrid as a high-capacity conversion-type anode material for lithium-ion batteries is investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic discharge/charge methods. The hybrid material demonstrates high specific capacity, good rate capability, and good long-term cyclability, which are far superior to those of the pristine Co3O4 material prepared under similar conditions. For example, the reversible charge capacities of the hybrid can reach 1100–1150 mAh g?1 at a lower current density of 0.1 or 0.2 A g?1 and remain 600 mAh g?1 at the high current density of 5 A g?1. After 300 cycles at 0.5 A g?1, a high charge capacity of 850 mAh g?1 is retained. The enhanced electrochemical performance is attributed to the incorporated VGCFs as well as the porous structure and the smaller nanograins of the Co3O4 active material.  相似文献   

15.
Pr-doped Li4Ti5O12 in the form of Li4?x/3Ti5?2x/3PrxO12 (x = 0, 0.01, 0.03, 0.05, and 0.07) was synthesized successfully by an electrospinning technique. ICP shows that the doped samples are closed to the targeted samples. XRD analysis demonstrates that traces of Pr3+ can enlarge the lattice parameter of Li4Ti5O12 from 8.3403 to 8.3765 Å without changing the spinel structure. The increase of lattice parameter is beneficial to the intercalation and de-intercalation of lithium-ion. XPS results identify the existence form of Ti is mainly Ti4+ and Ti3+ in minor quantity in Li4?x/3Ti5?2x/3PrxO12 (x = 0.05) samples due to the small amount of Pr3+. The transition from Ti4+ to Ti3+ is conducive to the electronic conductivity of Li4Ti5O12. FESEM images show that all the nanofibers are well crystallized with a diameter of about 200 nm and distributed uniformly. The results of electrochemical measurement reveal that the 1D Li4?x/3Ti5?2x/3PrxO12 (x = 0.05) nanofibers display enhanced high-rate capability and cycling stability compared with that of undoped nanofibers. The high-rate discharge capacity of the Li4?x/3Ti5?2x/3PrxO12 (x = 0.05) samples is excellent (101.6 mAh g?1 at 50 °C), which is about 58.48 % of the discharge capacity at 0.2 °C and 4.3 times than that of the bare Li4Ti5O12 (23.5 mA g?1). Even at 10 °C (1750 mA g?1), the specific discharge capacity is still 112.8 mAh g?1 after 1000 cycles (87.9 % of the initial discharge capacity). The results of cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) illustrate that the Pr-doped Li4Ti5O12 electrodes possess better dynamic performance than the pure Li4Ti5O12, further confirming the excellent electrochemical properties above.  相似文献   

16.
Manganese oxides of spinel structure, LiMn2O4, Li1-x Ni x Mn2O4 (0.25 ≤ x≤ 0.75), and NiMn2O4, were studied by EDS, XRD, SEM, magnetic (M-H, M-T), and XPS measurements. The samples were synthesized by an ultrasound-assisted sol-gel method. EDS analysis showed good agreement with the formulations of the oxides. XRD and Rietveld refinement of X-ray data indicate that all samples crystallize in the Fd3m space group characteristic of the cubic spinel structure. The a-cell parameter ranges from a = 8.2276 Å (x = 0) to a = 8.3980 Å (x = 1). SEM results showed particle agglomerates ranging in size from 2.3 μm (x = 0) down to 0.8 μm (x = 1). Hysteresis magnetization vs. applied field curves in the 5–300K range was recorded. ZFC-FC measurements indicate the presence of two magnetic paramagnetic-ferrimagnetic transitions. The experimental Curie constant was found to vary from 5 to 7.1 cm3 K mol?1 for the range of compositions studied (0 ≤ x ≤ 1). XPS studies of these oxides revealed the presence of Ni2+, Mn3+, and Mn4+. The experimental Ni/Mn atomic ratios obtained by XPS were in good agreement with the nominal values. A linear relationship of the average oxidation state of Mn with Ni content was observed. The oxide’s cation distributions as a function of Ni content from x = 0 ?Li+[Mn3+Mn4+]O4 to x = 1 \( {\mathrm{Ni}}_{0.35}^{2+}{\mathrm{Mn}}_{0.65}^{3+}\left[{\mathrm{Ni}}_{0.65}^{2+}\right.\left.{\mathrm{Mn}}_{1.35}^{3+}\right]{\mathrm{O}}_4 \) were proposed.  相似文献   

17.
Fast oxide-ion conductors La2Mo2-xWxO9 (x = 0–1) have been prepared using mechanochemical activation (MA) of starting oxides in a high-power planetary ball mill. Studies of La2Mo2-xWxO9 genesis and structural properties using thermal analysis, XRD, SEM, IR, and Raman spectroscopy have revealed that MA results in the formation of an amorphous precursor, while the cubic β-phase is formed after calcination at 700–900 °C. Due to a high dispersion of powders, high-density pellets of W-LAMOX ceramics have been obtained already after sintering at 950 °C. Their electrical conductivity measured by the impedance spectroscopy depends on the W concentration being sufficiently high (up to 5.6?10?3 S/cm at 630 °C) at temperatures below 650 °C.  相似文献   

18.
A series of spherical LiNi0.8Co0.15Ti0.05O2 cathode materials were synthesized through co-oxidation-controlled crystallization method followed by solid-state reaction at different calcination temperatures under oxygen flowing. The crystal structure and particles morphology of the as-prepared powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. All samples correspond to the layered α-NaFeO2 structure with R-3m space group. The LiNi0.8Co0.15Ti0.05O2 prepared at 800 °C presents a better hexagonal ordering structure and better spherical particles and possesses a high tap density of 3.22 g cm?3. Meanwhile, the NCT-2 sample exhibits an advanced electrochemical performance with an initial discharge capacity of 174.2 mAh g?1 and capacity retention of 86.7 % after 30 cycles at 0.2 C.  相似文献   

19.
Yuan Xia  Hui Wang 《Ionics》2016,22(2):159-166
Different particle sizes of dodecahedron precursors are synthesized by controlling the polarity of the solution. Through the results of scanning electron microscope (SEM) images, it can be found that different particle sizes of precursors present obvious edge angles and their morphology can be well retained after annealing. X-ray diffraction (XRD) measurements suggest that the annealed polyhedral products are pure single-phase NiCo2O4. When tested as lithium-ion battery anode, 0.5 μm NiCo2O4 polyhedra exhibits a specific capacity of 1050 mAh g?1 at 0.1 C at the 60th cycle, which was higher than theoretical capacity of single metal oxide (NiO 718 mAh g?1 and Co3O4 890 mAh g?1). It also exhibits the highest rate capability with an average discharge capacity of 890, 700, 490, 330, and 300 mAh g?1 at 0.5, 2, 4, 8, and 10 C, respectively. Those advantages are attributed to that small-sized particle with great surface areas decrease the actual current density at the surface and inner of the prepared electrode.  相似文献   

20.
Lithium vanadium-borate glasses with the composition of 0.3Li2O–(0.7-x)B2O3xV2O5 (x?=?0.3, 0.325, 0.35, 0.375, 0.4, 0.425, 0.45, and 0.475) were prepared by melt-quenching method. According to differential scanning calorimetry data, vanadium oxide acts as both glass former and glass modifier, since the thermal stability of glasses decreases with an increase in V2O5 concentration. Fourier transform infrared spectroscopy data show that the vibrations of [VO4] structural units occur at V2O5 concentration of 45 mol%. It is established that the concentration of V4+ ions increases exponentially with the growth of vanadium oxide concentration. Direct and alternative current measurements are carried out to estimate the contribution both electronic and ionic conductivities to the value of total conductivity. It is shown that the electronic conductivity is predominant in the total one. The glass having the composition of 0.3Li2O-0.275B2O3-0.475V2O5 shows the highest electrical conductivity that has the value of 7.4?×?10?5 S cm?1 at room temperature.  相似文献   

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