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1.
Spinel LiMn 2O 4 cathode materials were coated with 1.0, 3.0 and 5.0?wt.% of MgF 2 by precipitation, followed by heat treatment at 400?°C for 5?h in air. The effects of MgF 2 coating on the structural and electrochemical properties of LiMn 2O 4 cathodes were investigated using XRD, SEM, and electrochemical tests. XRD and SEM results show that no significant bulk structural differences are observed between the coated and pristine LiMn 2O 4. The charge–discharge tests show that the discharge capacity of LiMn 2O 4 decreases slightly, but the cyclability of LiMn 2O 4 is clearly improved when the amount of the MgF 2 coated was increased to 3.0?wt.%. The 3.0?wt.% MgF 2-coated LiMn 2O 4 exhibits capacity retention of 80.1 and 76.7 % after 100 cycles at room temperature (25?°C) and elevated temperature (55?°C) at a rate of 1?C, respectively, much higher than those of the bare LiMn 2O 4 (70.1 and 61.6 %). The improvement of electrochemical performance is attributed to the suppression of Mn dissolution into the electrolyte via the MgF 2 coating layer. 相似文献
2.
Ultrathin ZnO, ZrO 2, and Al 2O 3 surface coatings are deposited via atomic layer deposition (ALD) with high conformality and atomic scale thickness control to enhance the electrochemical performance of LiMn 2O 4 for applications in lithium ion batteries. Two types of ALD-modified LiMn 2O 4 electrodes are fabricated: one is ALD-coated LiMn 2O 4 composite electrode and the other is electrode composed of ALD-coated LiMn 2O 4 particles and uncoated carbon/polyvinylidenefluoride network. Cycling performance and cyclic voltammetric patterns reveal that ZnO ALD coating is the most effective protective film for improving the electrochemical performance of LiMn 2O 4 at either 25 or 55 °C, followed by ZrO 2 and Al 2O 3. After 100 electrochemical cycles in 1 C at 55 °C, the electrode consisting of LiMn 2O 4 particles coated with six ZnO ALD layers (as thin as ~1 nm) delivers the highest final capacity, more than twice that of the bare electrode. It is also found that amphoteric oxide coating on LiMn 2O 4 particles can enhance the cycleability of LiMn 2O 4 more effectively than coating on the composite electrode. Furthermore, for ALD coating either on the composite electrode or on LiMn 2O 4 particles, the effect of oxide ALD modification for improving capacity retention and increasing specific capacity of LiMn 2O 4 is more phenomenal at elevated temperature than at room temperature. 相似文献
3.
The surface of the spinel LiMn 2O 4 was coated with AlF 3 by a chemical process to improve its electrochemical performance at high temperatures. The morphology and structure of the
original and AlF 3-coated LiMn 2O 4 samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM). All the samples exhibited
a pure cubic spinel structure without any impurities in the XRD patterns. It was found that the surfaces of the original LiMn 2O 4 samples were covered with a nanolayer AlF 3 after the treatment. The charge/discharge of the materials were carried at 220 mA/g in the range of 3.0 and 4.4 V at 55°C.
While the original LiMn 2O 4 showed 17.8% capacity loss in 50 cycles at 55°C, the AlF 3-coated LiMn 2O 4 (118.1 mA h/g) showed only 3.4% loss of the initial capacity (122.3 mA h/g) at 55°C. It is obvious that the improvement in
cycling performance of the coated-LiMn 2O 4 electrode at 55°C is attributed to the presence of AlF 3 on the surface of LiMn 2O 4.
Published in Russian in Elektrokhimiya, 2009, Vol. 45, No. 7, pp. 817–819.
The article is published in the original 相似文献
4.
LiMn 2O 4 microcubes with a size of 10–15 μm have been synthesized by a facile self-templating route starting from cubic MnCO 3. The LiMn 2O 4 microcubes exhibit a hierarchical structure, where the cubes are stacked from parallel plates with a thickness of 200 nm, where each plate is composed of interconnected nanoparticles with a size of around 200 nm. The cubic LiMn 2O 4 shows excellent rate capability and high-rate cycling stability. At 10 C, it can yield a discharge capacity of 108 mAh g ?1. A discharge capacity of 88 mAh g ?1 can be retained after 100 cycles at 10 C. The excellent electrochemical performance makes it a promising cathode for high-power Li-ion batteries. 相似文献
5.
We reported a new method for the preparation of morphology-controllable LiMn 2O 4 particles. In this method, dimension-different MnO 2 nanowires synthesized hydrothermally by adjusting the reaction temperature were used as the precursor. The morphology and structure of the resulting products were characterized with scanning electron microscope and X-ray diffraction, and the performances of the prepared LiMn 2O 4 samples as cathode material of lithium batteries were investigated by cyclic voltammetry and galvanostatic charge/discharge test. The results indicate that the morphology of LiMn 2O 4 transforms from tridimensional particle (TP) to unidimensional rod (UR) through quadrate lamina (QL) with increasing the diameter and length of MnO 2 nanowires. Although the cyclic stabilities of LiMn 2O 4-TP, LiMn 2O 4-QL, and LiMn 2O 4-UR are very close (the 0.1 C capacity after 50 cycles is 101, 93, and 99 mAh g ?1 at 25 °C, and 84, 78, and 82 mAh g ?1 at 50 °C, respectively), LiMn 2O 4-QL delivers much higher rate capacity (about 70 mAh g ?1 at 5 C and 30 mAh g ?1 at 10 C) than LiMn 2O 4-TP and LiMn 2O 4-UR (about 20 mAh g ?1 at 5 C, 3 mAh g ?1 at 10 C, 25 mAh g ?1 at 5 C, and 3 mAh g ?1 at 10 C). 相似文献
6.
LiMn 2O 4 cathode materials with high discharge capacity and good cyclic stability were prepared by a simple one-step hydrothermal treatment of KMnO 4, aniline and LiOH solutions at 120–180 °C for 24 h. The aniline/KMnO 4 molar ratio ( R) and hydrothermal temperature exhibited an obvious influence on the component and phase structures of the resulting product. The precursor KMnO 4 was firstly reduced to birnessite when R was less than 0.2:1 at 120–150 °C. Pure-phased LiMn 2O 4 was formed when R was 0.2:1, and the LiMn 2O 4 was further reduced to Mn 3O 4 when R was kept in the range of 0.2–0.3 at 120–150 °C. Moreover, LiMn 2O 4 was fabricated when R was 0.15:1 at 180 °C. Octahedron-like LiMn 2O 4 about 300 nm was prepared at 120 °C, and particle size decreased with an increase in hydrothermal temperature. Especially, LiMn 2O 4 synthesized at 150 °C exhibited the best electrochemical performance with the highest initial discharge capacity of 127.4 mAh g −1 and cycling capacity of 106.1 mAh g −1 after 100 cycles. The high discharge capacity and cycling stability of the as-prepared LiMn 2O 4 cathode for rechargeable lithium batteries were ascribed to the appropriate particle size and larger cell volume. 相似文献
7.
Porous LiMn 2O 4 microsheets with micro-nanostructure have been successfully prepared through a simple carbon gel-combustion process with a microporous membrane as hard template. The crystal structure, morphology, chemical composition, and surface analysis of the as-obtained LiMn 2O 4 microsheets are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscope (XPS). It can be found that the as-prepared LiMn 2O 4 sample presents the two-dimensional (2-D) sheet structure with porous structure comprised with nano-scaled particles. As cathode materials for lithium-ion batteries, the obtained LiMn 2O 4 microsheets show superior rate capacities and cycling performance at various charge/discharge rates. The LiMn 2O 4 microsheets exhibit a higher charge and discharge capacity of 137.0 and 134.7 mAh g ?1 in the first cycle at 0.5 C, and it remains 127.6 mAh g ?1 after 50 cycles, which accounts for 94.7% discharge capacity retention. Even at 10 C rate, the electrode also delivers the discharge capacity of 91.0 mAh g ?1 after 300 cycles (93.5% capacity retention). The superior electrochemical properties of the LiMn 2O 4 microsheets could be attributed to the unique microsheets with porous micro-nanostructure, more active sites of the Li-ions insertion/deinsertion for the higher contact area between the LiMn 2O 4 nano-scaled particles and the electrolyte, and better kinetic properties, suggesting the applications of the sample in high-power lithium-ion batteries. 相似文献
8.
The effect of Al 2O 3 -coating on Li 3V 2(PO 4) 3/C cathode material for lithium-ion batteries has been investigated. The crystalline structure and morphology of the synthesized powders have been characterized by XRD, SEM, and HRTEM, and their electrochemical performances are evaluated by CV, EIS, and galvanostatic charge/discharge tests. It is found that Al 2O 3 -coating modification stabilizes the structure of the cathode material, decreases the polarization of electrode and suppresses the rise of the surface film resistance. Electrochemical tests indicate that cycling performance and rate capability of Al 2O 3-coated Li 3V 2(PO 4) 3/C are enhanced, especially at high rates. The Al 2O 3-coated material delivers discharge capacity of 123.03 mAh g ?1 at 4 C rate, and the capacity retention of 94.15 % is obtained after 5 cycles. The results indicate that Al 2O 3 -coating should be an effective way to improve the comprehensive properties of the cathode materials for lithium-ion batteries. 相似文献
9.
A comparative study of nanocrystalline spinel LiMn 2O 4 powders prepared by two different soft chemical routes such as solution and sol-gel methods using lithium and manganese acetates
are the precursors under different calcination temperatures. The dependence of the physicochemical properties of the spinel
LiMn 2O 4 powder has been extensively investigated by using thermal analysis (TGA/DTA), FTIR, X-ray diffraction studies, SEM, specific
surface area (BET) and electrical conductivity measurements. The results show that pure LiMn 2O 4 can be prepared from acetate precursors as starting materials at a low temperature of 600°C from solution route and 500°C
from sol-gel method. The charge-discharge characteristics and the cycling behavior of Li/1M LiBF 4-EC/DEC electrolyte / LiMn 2O 4cells revealed that LiMn 2O 4 calcined at higher temperatures showed a high initial capacity, while the LiMn 2O 4calcined at lower temperatures exhibited a good cycling behavior. 相似文献
10.
The Li-rich Li 1.3[Ni 0.35Mn 0.65]O 2+x microspheres are firstly prepared and subsequently transferred into the Al 2O 3-coated Li-rich Li 1.3[Ni 0.35Mn 0.65]O 2+x microspheres by a simple deposition method. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. The results reveal that the Al 2O 3-coated Li-rich Li 1.3[Ni 0.35Mn 0.65]O 2+x sample has a typical α-NaFeO 2 layered structure with the existence of Li 2MnO 3-type integrated component, and the Al 2O 3 layer is uniformly coated on the surface of the spherical Li-rich Li 1.3[Ni 0.35Mn 0.65]O 2+x particles with a thickness of about 4 nm. Importantly, the Al 2O 3-coated Li-rich sample exhibits obviously improved electrochemical performance compared with the pristine one, especially the 2 wt.% Al 2O 3-coated sample shows the best electrochemical properties, which delivers an initial discharge capacity of 228 mAh g ?1 at a rate of 0.1 C in the voltage of 2.0–4.6 V, and the first coulombic efficiency is up to 90 %. Furthermore, the 2 wt.% Al 2O 3-coated sample represents excellent cycling stability with capacity retention of 90.9 % at 0.33 C after 100 cycles, much higher than that of the pristine one (62.2 %). Particularly, herein, the typical inferior rate capability of Li-rich layered cathode is apparently improved, and the 2 wt.% Al 2O 3-coated sample also shows a high rate capability, which can deliver a capacity of 101 mAh g ?1 even at 10 C. Besides, the thin Al 2O 3 layer can reduce the charge transfer resistance and stabilize the surface structure of active material during cycling, which is responsible for the improvement of electrochemical performance of the Li-rich Li 1.3[Ni 0.35Mn 0.65]O 2+x . 相似文献
11.
In this study, a novel method was presented to improve the cycle performance of the spinel LiMn 2O 4 This method is quite different from the traditional way of coating LiMn 2O 4 particle itself with inorganic and organic compounds. First we covered the current collector with the mixture of LiMn 2O 4 particle, conductive agents and binders, and then deposited an aluminum film onto it by means of vacuum evaporation. The pure electrode and the modified electrode were investigated using a combination of scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and charge–discharge tests. The enhancement of the capacity retention of modified electrode is significant, maintaining 93.5% of the maximum capacity after 200 cycles at charge–discharge rate of C/2, while pure electrode only 63.7%. It was found that the improvement of cycling performance is greatly ascribed to the good electrical conductivity of aluminum film deposited on the surface of spinel LiMn 2O 4. 相似文献
12.
Spinel LiMn 2O 4 and Sm, La co-substituted LiSm x La 0.2-x Mn 1.80O 4 ( x?=?0.05, 0.10 and 0.15) cathode materials were synthesized by sol–gel method using aqueous solutions of metal nitrates and tartaric acid as chelating agent at 600 °C for 10 h. The structure and electrochemical properties of the synthesized materials were characterized by using thermogravimetric/differential thermal analysis, X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, charge/discharge and electrochemical impedance spectroscopy studies. XRD analysis indicated that all the prepared samples were mainly belong to cubic crystal form with F d3 m space group. LiSm 0.10La 0.10Mn 1.80O 4 exhibits capacity retention of 90 % and 82 % after 100 cycles at room temperature (30 °C) and at elevated temperature (50 °C) at a rate of 0.5-C, respectively, much higher than those of the pristine LiMn 2O 4 (74 % and 60 %). Among all the compositions, LiSm 0.10La 0.10Mn 1.80O 4 cathode has improved the structural stability, high-capacity retention, better elevated temperature performance and excellent electrochemical performances of the rechargeable lithium-ion batteries. 相似文献
13.
We report the synthesis of electrochemically active LiMn2O4 nanoparticles at varied temperature and pH values by sol–gel method using urea as a chelating and combusting agent. The effect of pH and annealing temperature on the structure, morphology and electrochemical performance was evaluated. The results obtained by XRD, SEM, TEM, and FTIR show that LiMn2O4 has uniform porous morphology and highly crystalline particles that can be obtained at pH 7.0 and 8.0 and at a relatively lower temperature of 600°C. Cyclic voltammetry measurements showed reversible redox reactions with fast kinetics corresponding to Li ions intercalation/deintercalation at 600°C at neutral pH 7.0. Charge/discharge studies carried out at a current rate of 40 mA g–1 reveal that LiMn2O4 synthesized at 600°C and pH 7.0 has the best structural stability and excellent cycling performance. 相似文献
14.
Spinel cathode materials consisting of LiMn 2O 4@LiNi 0.5Mn 1.5O 4 hollow microspheres have been synthesized by a facile solution‐phase coating and subsequent solid‐phase lithiation route in an atmosphere of air. When used as the cathode of lithium‐ion batteries, the double‐shell LiMn 2O 4@LiNi 0.5Mn 1.5O 4 hollow microspheres thus obtained show a high specific capacity of 120 mA h g ?1 at 1 C rate, and excellent rate capability (90 mAhg ?1 at 10 C) over the range of 3.5–5 V versus Li/Li + with a retention of 95 % over 500 cycles. 相似文献
15.
In this paper, La 0.4Ca 0.6CoO 3-coated LiNi 1/3Mn 1/3Co 1/3O 2 is successfully prepared by the sol–gel method associated with microwave pyrolysis method. The structure and electrochemical properties of the La 0.4Ca 0.6CoO 3-coated LiNi 1/3Co 1/3Mn 1/3O 2 are investigated by using X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. XRD analyses show that the La 0.4Ca 0.6CoO 3 coating does not change the structure of LiNi 1/3Co 1/3Mn 1/3O 2. The electrochemical performance studies demonstrate that 2 wt.% La 0.4Ca 0.6CoO 3-coated LiNi 1/3Co 1/3Mn 1/3O 2 powders exhibit the best electrochemical properties, with an initial discharge capacity of 156.9 mAh g –1 and capacity retention of 98.9 % after 50 cycles when cycled at a current density of 0.2 C between 2.75 and 4.3 V. La 0.4Ca 0.6CoO 3 coating can improve the rate performance because of the enhancement of the surface electronic/ionic transportation by the coating layer. EIS results suggest that the coating La 0.4Ca 0.6CoO 3 plays an important role in suppressing the increase of cell impedance with cycling especially for the increase of charge-transfer resistance. 相似文献
16.
The effects of methylene methanedisulfonate(MMDS) on the high-temperature(~50℃) cycle performance of LiMn_2O_4/graphite cells are investigated.By addition of 2 wt%MMDS into a routine electrolyte,the high-temperature cycling performance of LiMn204/graphite cells can be significantly improved.The analysis of differential capacity curves and energy-dispersive X-ray spectrometry(EDX) indicates that MMDS decomposed on both cathode and anode.The three-electrode system of pouch cell is used to reveal the capacity loss mechanism in the cells.It is shown that the capacity fading of cells without MMDS in the electrolytes is due to irreversible lithium consumption during cycling and irreversible damage of LiMn_2O_4 material,while the capacity fading of cell with 2 wt%MMDS in electrolytes mainly originated from irreversible lithium consumption during cycling. 相似文献
17.
Li[Ni 0.5Co 0.2Mn 0.3]O 2 coated with LiFePO 4 was synthesized by a co-precipitation method. It consisted of the parent Li[Ni 0.5Co 0.2Mn 0.3]O 2 as the core and the LiFePO 4 as the coating material, with an average particle diameter of 500 nm. The LiFePO 4-coated Li[Ni 0.5Co 0.2Mn 0.3]O 2 showed no large initial capacity drop in the first cycle, which generally occurred with cathode materials bearing inactive
coating layers such as Al 2O 3, ZnO, and MgO. Furthermore, it presented a remarkably improved cycle retention rate of over 89% until 400 cycles at 50 °C.
We suggest that the LiFePO 4 coating technique is a very effective tool to improve the cycle performance of Li[Ni 0.5Co 0.2Mn 0.3]O 2 at high temperatures. 相似文献
18.
Strategies for countering the solubility of LiMn 2O 4 (spinel) electrodes at 50 °C and for suppressing the reactivity of layered LiMO 2 (M=Co, Ni, Mn, Li) electrodes at high potentials are discussed. Surface treatment of LiMn 2O 4 with colloidal zirconia (ZrO 2) dramatically improves the cycling stability of the spinel electrode at 50 °C in Li/LiMn 2O 4 cells. ZrO 2-coated LiMn 0.5Ni 0.5O 2 electrodes provide a superior capacity and cycling stability to uncoated electrodes when charged to a high potential (4.6 V vs Li 0). The use of Li 2ZrO 3, which is structurally more compatible with spinel and layered electrodes than ZrO 2 and which can act as a Li +-ion conductor, has been evaluated in composite 0.03Li 2ZrO 3 · 0.97LiMn 0.5Ni 0.5O 2 electrodes; glassy Li xZrO 2 + x/2 (0< x⩽2) products can be produced from colloidal ZrO 2 for surface coatings. 相似文献
19.
LiMn 2O 4 spinel nanorods prepared from nanowire MnO 2 templates were capped with polyvinyl pyrrolidone (PVP) and coated with ZrC 2O 4 precursors in aqueous solution. Upon annealing at 600 °C in air, an amorphous ZrO 2 nanoscale coating layer was obtained on the spinel nanoparticles with a particle size of <100 nm that formed from the splitting of the original spinel nanorods. The electrochemical cycling results clearly showed that nanoscale ZrO 2 coating significantly improved the rate capability and cycle life at 65 °C in spite of very high surface area of the spinel nanoparticles. 相似文献
20.
The electrochemical properties of nanoscale Al 2O 3-coated LiCoO 2 thin films were examined as a function of the coating coverage. Al 2O 3-coated LiCoO 2 films showed enhanced cycle-life performance with increasing degree of coating coverage, which was attributed to the suppression
of Co dissolution and F − concentration in the electrolyte. Moreover, an Al 2O 3-coating layer with partial coverage clearly improved the electrochemical properties, even at 60 °C or with a water-contaminated
electrolyte. Even though metal-oxide coating on LiCoO 2 has been actively investigated, the mechanisms of nanoscale coating have yet to be clearly identified. In this article, surface
analysis suggested that the Al 2O 3-coating layer had transformed to an AlF 3
∙3H 2O layer during cycling, which inhibited the generation of HF by scavenging H 2O molecules present in the electrolyte. 相似文献
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