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1.
The carbon coated nanoflower-like Li4Ti5O12/C composites were prepared via hydrothermal method followed by surface modification using sucrose or polyvinylidene fluoride (PVDF) as carbon sources. X-ray diffraction, SEM, TEM, Raman spectroscopy, TGA, and the electrochemical measurements were used for the materials characterization. Such modification leads to the formation of a high-conductive carbon coating. In the case of polyvinylidene fluoride use, fluorination of Li4Ti5O12 surface takes place also. As a result, electrochemical performance of the obtained composites is improved. In the potential range of 1–3 V, Li4Ti5O12, Li4Ti5O12/CPVDF, and Li4Ti5O12/Csucrose exhibit, respectively, the discharge capacities of 142.5, 154.3, and 170.4 mAh/g at a current of 20 mA/g and 57.2, 82.1, and 89.3mAh/g at a current of 3200 mA/g. When cycled in a potential range of 0.01–3 V, the discharge capacity of Li4Ti5O12/CPVDF increases up to 252 mAh/g at 20 mA/g.  相似文献   

2.
Three kinds of LiFePO4 materials, mixed with carbon (as LiFePO4/C), doped with Ti (as Li0.99Ti0.01FePO4), and treated both ways (as Li0.99Ti0.01FePO4/C composite), were synthesized via ball milling by solid-state reaction method. The crystal structure and electrochemical behavior of the materials were investigated using X-ray diffraction, SEM, TEM, cyclic voltammetry, and charge/discharge cycle measurements. It was found that the electrochemical behavior of LiFePO4 could be increased by carbon coating and Ti-doping methods. Among the materials, Li0.99Ti0.01FePO4/C composite presents the best electrochemical behavior, with an initial discharge capacity of 154.5 mAh/g at a discharge rate of 0.2 C, and long charge/discharge cycle life. After 120 cycles, its capacity remains at 92% of the initial capacity. The Li0.99Ti0.01FePO4/C composite developed here can be used as the cathode material for lithium ion batteries.  相似文献   

3.
Li0.97Er0.01FePO4/C composite was prepared by solid-state reaction, using particle modification with amorphous carbon from the decomposition of glucose and lattice doping with supervalent cation Er3+. All samples were characterized by X-ray diffraction, scanning electron microscopy, multi-point Brunauer Emmett and Teller methodes. The electrochemical tests show Li0.97Er0.01FePO4/C composite obtains the highest discharge specific capacity of 154 mAh g−1 at C/10 rate and the best rate capability. Its specific capacity reaches 131 mAh g−1 at 2C rate. Its capacity loss is only 14.9 % when the rate varies from C/10 to 2C.  相似文献   

4.
Olivine-type LiFePO4 is a very promising polyanion-type cathode material for lithium-ion batteries. In this work, LiFePO4 with high specificity capacity is obtained from a novel precursor NH4FePO4·H2O via microwave processing. The grains grow up in the duration of sintering until they reach the decomposition temperature. The apparent conductivity of the samples rises rapidly with the irradiation time and influences the electrochemical performance of the material greatly at high current density. As a result, the LiFePO4 cathode material obtained with a sintering time of 15 min has good electrochemical performance. Between 2.5 and 4.2 V versus Li, a reversible capacity is as high as 156 mAh g−1 at 0.05 C.  相似文献   

5.
Carbon-coated Na2FePO4F is synthesized by a simple solid-state method with ascorbic acid as carbon source. Structural characterization of Na2FePO4F by synchrotron X-ray diffraction, scanning/transmission electron microscopy, and Raman spectroscopy reveals that ascorbic acid effectively suppresses the particle growth of Na2FePO4F, forming the nano-sized carbon coated materials. Electrode performance of Na2FePO4F for rechargeable sodium batteries is also examined. The carbon-coated Na2FePO4F sample (1.3 wt% carbon) delivers initial discharge capacity of 110 mAh g-1 at a rate of 1/20 C (6.2 mA g-1) with well-defined voltage plateaus at 3.06 and 2.91 V vs. Na metal. The sample also shows acceptable capacity retention and rate capability as the positive electrode materials for rechargeable Na batteries, which is operable at room temperature.  相似文献   

6.
Summary TG-DSC-MS (thermogravimetry-differential scanning calorimetry-mass spectrometry) coupling techniques were used to make a simultaneous characterizing study for the thermal decomposition process of the carbon nanotube (CNT)/SiO2precursor powders prepared by rapid sol-gel method. The thermal stability of the CNT and the SiO2pure gel were investigated by TG-DSC. The results showed that the oxidation of CNT began from 530 and combusted at about 678°C at the heating rate of 10°C min-1in air. Moreover, the faster the heating rate, the higher the temperature of CNT combustion. The appropriate calcinations temperature of the CNT/SiO2precursor powders should be held for 1 h at 500°C.  相似文献   

7.
LiNi0.80Co0.15Al0.05O2 (NCA) is explored to be applied in a hybrid Li+/Na+ battery for the first time. The cell is constructed with NCA as the positive electrode, sodium metal as the negative electrode, and 1 M NaClO4 solution as the electrolyte. It is found that during electrochemical cycling both Na+ and Li+ ions are reversibly intercalated into/de-intercalated from NCA crystal lattice. The detailed electrochemical process is systematically investigated by inductively coupled plasma-optical emission spectrometry, ex situ X-ray diffraction, scanning electron microscopy, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The NCA cathode can deliver initially a high capacity up to 174 mAh g?1 and 95% coulombic efficiency under 0.1 C (1 C?=?120 mA g?1) current rate between 1.5–4.1 V. It also shows excellent rate capability that reaches 92 mAh g?1 at 10 C. Furthermore, this hybrid battery displays superior long-term cycle life with a capacity retention of 81% after 300 cycles in the voltage range from 2.0 to 4.0 V, offering a promising application in energy storage.  相似文献   

8.
A solid-state reaction process with poly(vinyl alcohol) as the carbon source is developed to synthesize LiFePO4-based active powders with or without modification assistance of a small amount of Li3V2(PO4)3. The samples are analyzed by X-ray diffraction, scanning/transmission electron microscopy, and Raman spectroscopy. It is found that, in addition to the minor effect of a lattice doping in LiFePO4 by substituting a tiny fraction of Fe2+ ions with V3+ ions, the change in the form of carbon coating on the surface of LiFePO4 plays a more important role to improve the electrochemical properties. The carbon changes partially from sp3 to sp2 hybridization and thus causes the significant rise in electronic conductivity in the Li3V2(PO4)3-modified LiFePO4 samples. Compared with the carbon-coated baseline LiFePO4, the composite material 0.9LiFePO4·0.1Li3V2(PO4)3 shows totally different carbon morphology and much better electrochemical properties. It delivers specific capacities of 143.6 mAh g?1 at 10 C rate and 119.2 mAh g?1 at 20 C rate, respectively. Even at the low temperature of ?20 °C, it delivers a specific capacity of 118.4 mAh g?1 at 0.2 C.  相似文献   

9.
Self-supported and binder-free electrodes based on homogeneous Co3O4/TiO2 nanotube arrays enhanced by carbon layer and oxygen vacancies (Co3O4/co-modified TiO2 nanotube arrays (m-TNAs)) are prepared via a simple and cost-effective method in this paper. The highly ordered TNAs offer direct pathways for electron and ion transport and can be used as 3D substrate for the decoration of electroactive materials without any binders. Then, by a facile one-step calcination process, the electrochemical performance of the as-obtained carbon layer and oxygen vacancy m-TNAs is approximately 83 times higher than that of pristine TNAs. In addition, Co3O4 nanoparticles are uniformly deposited onto the m-TNAs by a universal chemical bath deposition (CBD) process to further improve the supercapacitive performance. Due to the synergistic effect of m-TNAs and Co3O4 nanoparticles, a maximum specific capacitance of 662.7 F g?1 can be achieved, which is much higher than that of Co3O4 decorated on pristine TNAs (Co3O4/TNAs; 166.2 F g?1). Furthermore, the specific capacitance retains 86.0 % of the initial capacitance after 4000 cycles under a high current density of 10 A g?1, revealing the excellent long-term electrochemical cycling stability of Co3O4/m-TNAs. Thus, this kind of heterostructured Co3O4/m-TNAs could be considered as promising candidates for high-performance supercapacitor electrodes.  相似文献   

10.
The key parameters related to cathode materials for commercial use are a high specific capacity, good cycling stability, capacity retention at high current rates, as well as the simplicity of the synthesis process. This study presents a facile synthesis of a composite cathode material, Li2FeSiO4 with carbon, under extreme conditions: rapid heating, short dwell at 750 °C and subsequent quenching. The water-soluble polymer methylcellulose was used both as an excellent dispersing agent and a carbon source that pyrolytically degrades to carbon, thereby enabling the homogeneous deployment of the precursor compounds and the control of the Li2FeSiO4 particle growth from the earliest stage of processing. X-ray powder diffraction reveals the formation of Li2FeSiO4 nanocrystallites with a monoclinic structure in the P21/n space group (#14). The composite’s electrochemical performance as a cathode material in Li-ion batteries was examined. The influence of the amount of methylcellulose on the microstructural, morphological, conductive, and electrochemical properties of the obtained powders has been discussed. It has been shown that the overall electrochemical performance is improved with an increase of carbon content, through both the decrease of the mean particle diameter and the increase of electrical conductivity.  相似文献   

11.
Olivine LiFePO4 is challenged by its poor electronic and ionic conductivities for lithium-ion batteries. Polyethylene glycol (PEG) has been applied for LiFePO4 preparation by different research groups, but there is no consensus on the influence of the mean molecular weight of PEG on the structure and electrochemical performances of LiFePO4/C composites. In this work, LiFePO4/C composites were prepared by using micronsized FePO4·2H2O powder as starting material, PEG (mean molecular weight of 200, 400, 4000 or 10000) and citric acid as complex carbon source. The structure and electrochemical performances of LiFePO4/C composites would be decided considerably by the mean molecular weight of PEG, and the sample using PEG200 exhibited the least inter-particle agglomeration, the smallest charge transfer resistance and the highest discharge capacity. A probable growth mechanism is also proposed based on SEM images and electrochemical results: with the assistance of citric acid, PEG molecule with small molecular weight tends to cover one or only a few micron-sized FePO4·2H2O particles, significantly suppress the agglomeration of primary LiFePO4 particles and thus result in uniform particle-size distribution and carbon coating.  相似文献   

12.
Natural graphite treated by mechanical activation can be directly applied to the preparation of Li3V2(PO4)3. The carbon-coated Li3V2(PO4)3 with monoclinic structure was successfully synthesized by using natural graphite as carbon source and reducing agent. The amount of activated graphite is optimized by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectrum, galvanostatic charge/discharge measurements, cyclic voltammetry, and electrochemical impedance spectroscopy tests. Our results show that Li3V2(PO4)3 (LVP)-10G exhibits the highest initial discharge capacity of 189 mAh g?1 at 0.1 C and 162.9 mAh g?1 at 1 C in the voltage range of 3.0–4.8 V. Therefore, natural graphite is a promising carbon source for LVP cathode material in lithium ion batteries.  相似文献   

13.
Spinel LiNi0.5Mn1.5O4 cathode material is a promising candidate for next-generation rechargeable lithium-ion batteries. In this work, BiFeO3-coated LiNi0.5Mn1.5O4 materials were prepared via a wet chemical method and the structure, morphology, and electrochemical performance of the materials were studied. The coating of BiFeO3 has no significant impact on the crystal structure of LiNi0.5Mn1.5O4. All BiFeO3-coated LiNi0.5Mn1.5O4 materials exhibit cubic spinel structure with space group of Fd3m. Thin BiFeO3 layers were successfully coated on the surface of LiNi0.5Mn1.5O4 particles. The coating of 1.0 wt% BiFeO3 on the surface of LiNi0.5Mn1.5O4 exhibits a considerable enhancement in specific capacity, cyclic stability, and rate performance. The initial discharge capacity of 118.5 mAh g?1 is obtained for 1.0 wt% BiFeO3-coated LiNi0.5Mn1.5O4 with very high capacity retention of 89.11% at 0.1 C after 100 cycles. Meanwhile, 1.0 wt% BiFeO3-coated LiNi0.5Mn1.5O4 electrode shows excellent rate performance with discharge capacities of 117.5, 110.2, 85.8, and 74.8 mAh g?1 at 1, 2, 5, and 10 C, respectively, which is higher than that of LiNi0.5Mn1.5O4 (97.3, 90, 77.5, and 60.9 mAh g?1, respectively). The surface coating of BiFeO3 effectively decreases charge transfer resistance and inhibits side reactions between active materials and electrolyte and thus induces the improved electrochemical performance of LiNi0.5Mn1.5O4 materials.  相似文献   

14.
Magnetite (Fe3O4) nanoparticles anchored over the different active carbon supports were developed by a simple wet solution method. The developed nanostructures were magnetically self-assembled over the electrode surface and exploited as anode catalysts in mediatorless microbial fuel cells (MFC). The morphological characterizations revealed that 3~8-nm-sized Fe3O4 nanoparticles were homogeneously anchored over the different carbon matrices and the obtained diffraction patterns ensured the cubic inverse spinel structure of prepared Fe3O4 nanoparticles. The morphology, size, and structure of Fe3O4 nanoparticles anchored over the different active carbon supports were maintained identical, and the influence of active carbon support toward the effectual MFC performances was evaluated under various electrochemical regimes and conditions by using Escherichia coli as a catalytic microorganism. The electrochemical characterizations revealed that carbon nanotube (CNT)-supported Fe3O4 nanoparticles exhibited lower charge transfer resistance and high coulombic efficiency in comparison with the graphene and graphite nanofiber-supported composites. Among the studied anode catalysts, Fe3O4/CNT composite exhibited the maximum MFC power density of 865 mW m?2 associated with excellent durability performances, owing to the specific interaction exerted between the microorganisms and the Fe3O4/CNT composite. Thus, the binder-free electrode modification process, mediatorless environment, rapid electron transfer kinetics, high power generation, and long durability performances achieved for the developed system paved futuristic dimensions for the high performance MFCs.  相似文献   

15.
The preparation of a carbon ceramic electrode modified with SnO2 (CCE/SnO2) using tin dibutyl diacetate as precursor was optimized by a 23 factorial design. The factors analyzed were catalyst (HCl), graphite/organic precursor ratio, and inorganic precursor (dibutyltin diacetate). The statistical treatment of the data showed that only the second-order interaction effect, catalyst × inorganic precursor, was significant at 95% confidence level, for the electrochemical response of the system. The obtained material was characterized by scanning electron microscopy (MEV), X-ray diffraction (XRD), RAMAN spectroscopy, XPS spectra, and voltammetric techniques. From the XPS spectra, it was confirmed the formation of the Si–O–Sn bond by the shift in the binding energy values referred to Sn 3d3/2 due to the interaction of Sn with SiOH species. The incorporation of SnO2 provided an increment of the electrode response for levofloxacin, with Ipa = 147.0 μA for the ECC and Ipa = 228.8 μA for ECC/SnO2, indicating that SnO2 when incorporated into the silica network enhances the electron transfer process. Under the optimized working conditions, the peak current increased linearly with the levofloxacin concentration in the range from 6.21×10?5 to 6.97×10?4 mol L?1 with quantification and detection limits of 3.80×10?5 mol L?1 (14.07 mg L?1) and 1.13×10?5 mol L?1 (4.18 mg L?1), respectively.  相似文献   

16.
Spinel phase Li4Ti5O12 (s-LTO) with an average primary particle size of 150 nm was synthesised via a solid state route by calcining a precursor mixture at 600 °C. The precursor was prepared from a stoichiometric mixture of TiO2 nanoparticles and an ethanolic solution of Li acetate and activated by ball-milling. Effects of the calcination temperature and atmosphere are examined in relation to the coexistence of impurity phases by X-ray diffraction and 6Li MAS NMR. The charge capacity of s-LTO, determined from cyclic voltammogram at a scan rate of 0.1 mV/s, was 142 mAh/g. The capacity of our optimised material is superior to that of commercially available spinel (a-LTO), despite the considerably smaller BET-specific surface area of the former. The superior properties of our material were also demonstrated by galvanostatic charging/discharging. From these observations, we conclude that the presented low-temperature solid state synthesis route provides LTO with improved electrochemical performance.  相似文献   

17.
Li2ZnTi3O8/C nanocomposite has been synthesized using phenolic resin as carbon source in this work. The structure, morphology, and electrochemical properties of the as-prepared Li2ZnTi3O8 samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), Raman spectroscopy (RS), galvanostatic charge–discharge, and AC impedance spectroscopy. SEM images show that Li2ZnTi3O8/C was agglomerated with a primary particle size of ca. 40 nm. TEM images reveal that a homogeneous carbon layer (ca. 5 nm) formed on the surface of Li2ZnTi3O8 particles which is favorable to improve the electronic conductivity and inhibit the growth of Li2ZnTi3O8 during annealing process. The as-prepared Li2ZnTi3O8/C composite with 6.0 wt.% carbon exhibited a high initial discharge capacity of 425 and 159 mAh g?1 at 0.05 and 5 A g?1, respectively. At a high current density of 1 A g?1, 95.5 % of its initial value is obtained after 100 cycles.  相似文献   

18.
Li[Ni1/3Co1/3Mn1/3]O2 (NCM 111) is a promising alternative to LiCoO2, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g?1 is quite low, and cycling at potentials above 4.5 V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO2 (R-3m, M?=?Ni, Co) and a shell of Li2MnO3 (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li+/Ni2+ cation disorder and stronger M*–O (M*?=?Mn, Co, Ni) bonds than NCM 111. The core–shell material Li1.15Na0.5(Ni1/3Co1/3)core(Mn1/3)shellO2 can be cycled to a high upper cutoff potential of 4.7 V, delivers a high discharge capacity of 218 mAh g?1 at 20 mA g?1, and retains 90 % of its discharge capacity at 100 mA g?1 after 90 cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density.
Graphical Abstract Average voltage vs. number of cycles for the core–shell and pristine materials at 20 mA g?1 for 10 cycles followed by 90 cycles at 100 mA g?1
  相似文献   

19.
We have studied LiFePO4/C nanocomposites prepared by sol-gel method using lauric acid as a surfactant and calcined at different temperatures between 600 and 900 °C. In addition to the major LiFePO4 phase, all the samples show a varying amount of in situ Fe2P impurity phase characterized by x-ray diffraction, magnetic measurements, and Mössbauer spectroscopy. The amount of Fe2P impurity phase increases with increasing calcination temperature. Of all the samples studied, the LiFePO4/C sample calcined at 700 °C which contains ~15 wt% Fe2P shows the least charge transfer resistance and a better electrochemical performance with a discharge capacity of 136 mA h g?1 at a rate of 1 C, 121 mA h g?1 at 10 C (~70 % of the theoretical capacity of LiFePO4), and excellent cycleability. Although further increase in the amount of Fe2P reduces the overall capacity, frequency-dependent Warburg impedance analyses show that all samples calcined at temperatures ≥700 °C have an order of magnitude higher Li+ diffusion coefficient (~1.3?×?10?13 cm2 s?1) compared to the one calcined at 600 °C, as well as the values reported in literature. This work suggests that controlling the reduction environment and the temperature during the synthesis process can be used to optimize the amount of conducting Fe2P for obtaining the best capacity for the high power batteries.  相似文献   

20.
Li4Ti5O12/Li2TiO3 composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li4Ti5O12/Li2TiO3 composite nanofibers exhibit initial discharge capacity of 216.07 mAh g?1 at 0.1 C, rate capability of 151 mAh g?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g?1 after 1000 cycles at 20 C. Compared with pure Li4Ti5O12 nanofibers and Li2TiO3 nanofibers, Li4Ti5O12/Li2TiO3 composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li2TiO3 which could strengthen the structure stability of the hosted materials and has fast Li+-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li4Ti5O12 anodes for lithium rechargeable batteries.  相似文献   

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