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1.
The Si–SiC nanocomposites were synthesized by high-energy mechanical milling (HEMM) using two different starting mixtures, Si:SiC=1:2 and Si:C=3:2. Both mixtures result in amorphous silicon and nanocrystalline silicon carbide as confirmed by XRD results. The Si–SiC nanocomposite corresponding to Si:SiC=1:2 obtained after milling for 30 h shows a capacity as high as 370 mAh/g. The nanocomposite synthesized using HEMM for 24 h from a mixture corresponding to Si:C=3:2 also exhibits a stable capacity of 370 mAh/g. Transmission electron microscopy (TEM) analysis shows that SiC nanocrystallites 10 nm in size are distributed homogeneously within the nanocomposite. Electron energy-loss spectroscopy (EELS) maps of C suggests that SiC is uniformly present within the particles.  相似文献   

2.
《Journal of power sources》2006,158(1):557-563
Composites comprising silicon (Si), graphite (C) and polyacrylonitrile-based disordered carbon (PAN-C), denoted as Si/C/PAN-C, have been synthesized by thermal treatment of mechanically milled silicon, graphite, and polyacrylonitrile (PAN) powder of nominal composition C–17.5 wt.% Si–30 wt.% PAN. PAN acts as a diffusion barrier to the interfacial diffusion reaction between graphite and Si to form the electrochemically inactive SiC during prolonged milling of graphite and Si, which could be easily formed in the absence of PAN. In addition, graphite, which contributes to the overall capacity of the composite and suppresses the irreversible loss, retains its graphitic structure during prolonged milling in the presence of PAN. The resultant Si/C/PAN-C based composites exhibit a reversible capacity of ∼660 mAh g−1 with an excellent capacity retention displaying almost no fade in capacity when cycled at a rate of ∼C/4. Scanning electron microscopy (SEM) analysis indicates that the structural integrity and microstructural stability of the composite during the alloying/dealloying process appear to be the main reasons contributing to the good cyclability observed in the above composites.  相似文献   

3.
《Journal of power sources》2006,153(2):371-374
Cu5Si–Si/C composites with precursor atomic ratio of Si:Cu = 1, 2 and 4.5 have been produced by high-energy ball-milling of a mixture of copper–silicon alloy and graphite powder for anode materials of lithium-ion battery. X-ray diffraction and scanning electron microscope measurements show that Cu5Si alloy is formed after the intensive ball milling and alloy particles along with low-crystallite Si are interspersed in graphite uniformly. Cu5Si–Si/C composite electrodes deliver a larger reversible capacity than commercialized graphite and better cyclability than silicon. The increase of copper amount in the composites decreases reversible capacity but improves cycling performance. Cu5Si–Si/C composite with Si:Cu = 1 demonstrates an initial reversible capacity of 612 mAh g−1 at 0.2 mA cm−2 in the voltage range from 0.02 to 1.5 V. The capacity retention is respectively 74.5 and 70.0% at the 40th cycle at the current density of 0.2 and 1 mA cm−2.  相似文献   

4.
《Journal of power sources》2006,159(1):307-311
Small crystallites LiFePO4 powder with conducting carbon coating can be synthesized by ultrasonic spray pyrolysis. Cheaper trivalent iron ion is used as the precursor. The pure olivine phase can be prepared with the duplex process of spray pyrolysis (synthesized at 450, 550 or 650 °C) and subsequent heat-treatment (at 650 °C for 4 h). The results indicate that the pyrolysis temperature of 450 °C is appropriate for best results. The carbon coating on the LiFePO4 surface is critical to the electrochemical performance of LiFePO4 cathode materials of the lithium secondary battery, since the carbon coating does not only increase the electronic conductivity via carbon on the surface of particles, but also enhance the ion mobility of lithium ion due to prohibiting the grain growth during post-heat-treatment. The carbon of 15 wt.% evenly distributed on the final LiFePO4 powders can get the highest initial discharge capacity of 150 mA h g−1 at C/10 and 50 °C.  相似文献   

5.
This study examines the effect of heat-treatment temperature on the electrochemical corrosion of carbon nanofibers (CNFs) in polymer electrolyte membrane (PEM) fuel cells. Corrosion is investigated by monitoring the generation of CO2 using an on-line mass spectrometer at a constant potential of 1.4 V for 30 min. The experimental results show that the generation of CO2 decreases with increasing heat-treatment temperature, indicating that less electrochemical carbon corrosion occurs. In particular, when the heat-treatment temperature is 2400 °C, the change intensifies. X-ray photoelectron spectroscopic analysis shows that oxygen functional groups on the carbon surface decrease with increasing heat-treatment temperature. A reduction in oxygen functional groups increases the hydrophobic nature of the carbon surface, which is responsible for the increased corrosion resistance of CNFs.  相似文献   

6.
《Journal of power sources》2006,163(1):211-214
We have investigated the structural and electrochemical properties of Cu–Si nanocomposite electrode fabricated by co-sputtering method. Reversible capacity of an amorphous Si electrode is degraded continuously with increasing cycle number up to 40 cycles. However, a Cu–Si nanocomposite electrode, where Cu nano-dots are embedded in an amorphous Si matrix, shows an excellent reversible capacity with a stable value of ca. 400 μA h cm−2 μm−1 up to 40 cycles. The improved reversible capacity of the Cu–Si nanocomposite electrodes is attributed to the enhanced structural stability of the electrodes due to the presence of the Cu nano-dots evenly distributed throughout the Si matrix.  相似文献   

7.
MgH2 nanocomposites with ZrCrNi alloy obtained by high energy ball-milling were studied as-milled and after several hydriding-deydriding cycles. The microstructure and morphology of the samples was characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns show that no phase formation between MgH2 and elements of the alloys takes place during milling and after cycling. Different morphology of the powders as-milled and after cycling was observed by SEM. Pressure-composition isotherms of these composites were obtained in the pressure and temperature range of 0.1–15 bar and 200–300 °C respectively. The maximum reversible storage capacity was found to be 6.2 wt% at 300 °C. Absorption/desorption kinetics data at pressures of 0.1–5.0 bar and temperatures of 275 °C and 300 °C show that an activation process of about 20 cycles at 300 °C is necessary for stabilization of the kinetics and for achievement of the full hydrogen capacity. The thermodynamic parameters, i.e. enthalpy of formation and dissociation calculated using Van't Hoff plots, were found to be 73.53 kJ mol?1 and 87.63 kJ mol?1 respectively, in agreement with MgH2 data reported in literature.  相似文献   

8.
《Journal of power sources》2004,129(1):96-100
We have found that a Si film vacuum deposited on a Ni foil has a Li insertion capacity over 2000 mAh/g with cycleability over 1000 cycles, but a great issue was its difficulty to obtain a sufficiently thicker film capable of high current charge/discharge. In the present paper the examination of the high current charge/discharge performance of thicker Si film in relation to the film formation condition. The electrochemical evaluation was performed with cyclic voltammetry (CV) and constant current charge/discharge test with various loading currents in PC containing 1 M LiClO4.A Si film prepared with a rapid deposition rate gave a discharge capacity over 2000 mAh/g even with a very high charge/discharge rate over 10 C. In addition, the surface roughening of the substrate foil was found to play an important role to provide a thick film capable of high current performance. The constant discharge curve gave a wide plateau in the potential range between 200 and 500 mV versus Li/Li+. The XRD pattern of the deposited film gave no peaks due to Si, indicating the film to be amorphous. The SEM image of the deposited film was rather homogeneous, and after 500 cycles it still covered the entire surface of the Ni substrate though the surface became inhomogeneous.  相似文献   

9.
《Journal of power sources》2006,160(1):523-528
Olivine–LiCoPO4 powders have been processed by mechanical grinding for time periods ranging from 0.5 to 10 h with conductive carbon contents of 0, 8 and 20% (w/w). In all cases the grinding process produces an amorphization of the crystalline materials and decreases both the crystallite and particle sizes. Secondary phases are detected by scanning electron microscopy and X-ray diffraction in the materials milled for times greater than 2 h without carbon. The addition of conductive carbon during the milling process decelerates the degradation of the material and secondary phases are not detected even after 10 h of grinding. The electrochemical performance of olivine–LiCoPO4 is improved in all the materials milled for 0.5 h; a lower cell polarization and a larger reversible specific capacity are observed. These characteristics are enhanced in the materials grinded with conductive carbon, which also display a capacity retention with cycling clearly superior to that of the fresh LiCoPO4. Ball milling LiCoPO4 for times greater than 1 h is detrimental for the response of the electrode, independently on the amount of conductive carbon in the grinding media.  相似文献   

10.
《Journal of power sources》2002,107(1):103-109
Polymer electrolytes consisting of poly(ethylene oxide) (PEO) and lithium salts, such as LiCF3SO3 and LiBF4 are prepared by the ball-milling method. This is performed at various times (2, 4, 8, 12 h) with ball:sample ratio of 400:1. The electrochemical and thermal characteristics of the electrolytes are evaluated. The structure and morphology of PEO–LiX polymer electrolyte is changed to amorphous and smaller spherulite texture by ball milling. The ionic conductivity of the PEO–LiX polymer electrolytes increases by about one order of magnitude than that of electrolytes prepared without ball milling. Also, the ball milled electrolytes have remarkably higher ionic conductivity at low temperature. Maximum ionic conductivity is found for the PEO–LiX prepared by ball milling for 12 h, viz. 2.52×10−4 S cm−1 for LiCF3SO3 and 4.99×10−4 S cm−1 for LiBF4 at 90 °C. The first discharge capacity of Li/S cells increases with increasing ball milling time. (PEO)10LiCF3SO3 polymer electrolyte prepared by ball milling show the typical two plateau discharge curves in a Li/S battery. The upper voltage plateau for the polymer electrolyte containing LiBF4 differs markedly from the typical shape.  相似文献   

11.
《Journal of power sources》2006,161(2):1319-1323
A carbon-coated Si–Cu3Si composite material is prepared using silicon and copper(II) d-gluconate powders by simple mechanical milling and pyrolysis, and is investigated as an anode material for lithium-ion batteries. In this process, the Cu3Si and pyrolyzed carbon uniformly adhere to the surface of the silicon particles. The cycling performance of the composite material exhibits a stable capacity of 850 mAh g−1 for 30 cycles. The improved cycling performance is attributed to the fact that the copper silicide and pyrolyzed carbon provide both a better electrical contact with the current–collector and a buffering effect for the volume expansion–contraction during cycling.  相似文献   

12.
《Journal of power sources》2004,136(2):303-306
A thin film of Si was vacuum-deposited onto a 30 μm thick Ni foil from a source of n-type of Si, the film thickness examined being 200–1500 Å. Li insertion/extraction evaluation was performed mainly with cyclic voltammetry (CV) and constant current charge/discharge cycling in propylene carbonate (PC) containing 1 M LiClO4 at ambient temperature. The cycleability and the Li accommodation capacity were found to depend on the film thickness. Thinner films gave larger accommodation capacity. A 500 Å thick Si film gave a charge capacity over 3500 mAh g−1 being maintained during 200 cycles under 2 C charge/discharge rate, while a 1500 Å film revealed around 2200 mAh g−1 during 200 cycles under 1 C rate. The initial charge loss could not be ignored but it could be reduced by controlling the deposition conditions.  相似文献   

13.
《Journal of power sources》2003,124(2):513-517
Composite electrodes of amorphous vanadium pentoxide/carbon/ceramic filler were prepared by mixing vanadium oxide hydrosol, acetone, carbon and ceramic fillers, and by extension on aluminum foil. High rate charge/discharge property of the composite electrode was examined, and the effect of fillers was discussed. The composite electrode had a porous structure, in which pores were 0.5–3 μm in diameter and penetrated through the composite. The composite electrode showed a large capacity of 98 mA h/g-electrode at a high current density of 17.2 mA/cm2 (270 A/g-electrode). The relation between discharge capacity and current density was calculated by solving the simplified diffusion equation. The apparent diffusion coefficient of lithium ion in the composite electrode was found to be 10 times larger than that of electrode without fillers.  相似文献   

14.
Nano-SnO2/carbon composite materials were synthesized in situ using the polyol method by oxidizing SnCl2·2H2O in the presence of a carbon matrix. All the as-synthesized composites consisted of SnO2 nanoparticles (5–10 nm) uniformly embedded into the carbon matrix as evidenced by TEM. XRD confirmed the presence of nano-sized SnO2 particles that are crystallized in a rutile structure and XPS revealed a tin oxidation state of +4. Cyclic voltammetry of the composites showed an irreversible peak at 1.4 V in the first cycle and a typical alloying/de-alloying process at 0.1–0.5 V. The best composite (“composite I”, 15 wt% SnO2) showed an improved lithium storage capacity of 370 mAh g?1 at 200 mA g?1 (~C/2) which correspond to 32% improvement and lower capacity fade compared to commercial SnO2 (50 nm). We have also investigated the effect of the heating method and we found that the use of a microwave was beneficial in not only shortening reaction time but also in producing smaller SnO2 particles that are also better dispersed within the carbon matrix which also resulted in higher lithium storage capacity.  相似文献   

15.
《Journal of power sources》2006,158(1):654-658
Li[Ni1/3Co1/3Mn1/3]O2 was prepared by mixing uniform co-precipitated spherical metal hydroxide (Ni1/3Co1/3Mn1/3)(OH)2 with 7% excess LiOH followed by heat-treatment. The tap-density of the powder obtained was 2.38 g cm−3, and it was characterized using X-ray diffraction (XRD), particle size distribution measurement, scanning electron microscope-energy dispersive spectrometry (SEM-EDS) and galvanostatic charge–discharge tests. The XRD studies showed that the material had a well-ordered layered structure with small amount of cation mixing. It can be seen from the EDS results that the transition metals (Ni, Co and Mn) in Li[Ni1/3Co1/3Mn1/3]O2 are uniformly distributed. Initial charge and discharge capacity of 185.08 and 166.99 mAh g−1 was obtained between 3 and 4.3 V at a current density of 16 mA g−1, and the capacity of 154.14 mAh g−1 was retained at the end of 30 charge–discharge cycles with the capacity retention of 93%.  相似文献   

16.
《Journal of power sources》2005,141(2):286-292
Sn-based alloy compounds have been considered as possible alternatives for carbon in lithium-ion batteries and attract great attentions because of their large electrochemical capacity compared with that of carbon. In this work, a multilayered Sn–Zn/Zn/Cu alloy thin-film electrode has been prepared by electroplating method. The structure and performance of the electrode before and after heat treatment have been investigated. It is found that Cu6Sn5 phase and multilayered structure in electrode are formed after heat treatment. This optimized structure of the heat-treated electrode results in enhanced cycle life. The capacity of the electrode is over 320 mA h g−1 after 100 cycles; though it is 83 mA h g−1 after 20 cycles for as-plated electrode. The Sn–Cu and Zn–Cu alloy formed a network in the electrode is considered to strengthen the electrode and reduce the effect of volume expansion and phase transition during cycling. Experimental results also reveal that lower cut-off potential (0.05 V) for charging and higher one (1.2 V) for discharging result in long cycle life and high discharge capacity, respectively. The reason of capacity decay of the heat-treatment electrode during cycling has also been investigated. All these results show that the electroplated Sn–Zn-based alloy film on Cu foil would be a promising negative material with high capacity and low cost for Li secondary batteries.  相似文献   

17.
《Journal of power sources》2005,140(1):139-144
The effects of Si particle size and the amount of carbon-based conductive additive (CA) on the performance of a Si anode in a Li-ion battery are investigated by adopting combinations of two different Si particle sizes (20 and 3 μm on average) and CA contents (15 and 30 wt.%), respectively. The CA contains graphitic flakes and nano-sized carbon black. Cyclic voltammetry, charge–discharge tests, scanning electron microscopy and X-ray diffraction establish that the CA content has a profound effect on the cycle-life and irreversible capacity of the Si anode. The former increases, while the latter decreases significantly with increasing CA content. Reducing the particle size of Si, on the other hand, facilitates the alloying/de-alloying kinetics. For instance a cycle-life of over 50 cycles with >96% capacity retention at a charge capacity of 600 mAh per g-Si has been demonstrated by adopting of 30 wt.% CA and 3 μm Si particles.  相似文献   

18.
《Journal of power sources》2006,159(1):163-166
Mg–Ce alloy was prepared by induction melting under vacuum, hydrided firstly and then Mg–Ce/Ni composite was obtained by mechanical milling Mg–Ce hydrides under Ar for 50 h with addition of nano-sized Ni powder. XRD results showed CeMg12 formed in melted alloy. CeMg12 disappeared and CeH2.53 emerged during subsequent hydriding. The phase composition was not changed during ball milling process. Compared with Mg and Mg/Ni, Mg–Ce/Ni composite showed significant hydriding/dehydriding performance without any prior activation. The enthalpy of hydride formation for Mg–10.9 wt.% Ce/10 wt.% Ni composite was −70.58 kJ mol−1 H2. Improved hydrogen storage properties were attributed to the catalytic effect of addition of nano-sized Ni particles and existence of CeH2.53, as well as the grain refinement, defects, etc. in the material introduced by ball milling process.  相似文献   

19.
Electrochemically active Si0.66Sn0.34 (SiSn) composite alloys dispersed in a carbon (graphite) matrix were synthesized using both wet and dry high-energy mechanical milling (HEMM). The resultant composites are comprised of amorphous carbon (in the case of dry HEMM) or crystalline carbon (in the case of wet HEMM), and crystalline silicon and tin (for both cases) as verified by X-ray diffraction (XRD). The XRD results also indicate the presence of iron–tin intermetallic (FeSn2) arising as a contaminant during dry HEMM. The composite composition of 85C–15[Si0.66Sn0.34] (mol%) resulted in reversible discharge capacities as high as 800 mAh g−1 with a reasonable capacity retention (1.36% loss/cycle). Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analyses were further conducted to examine the surface of the electrode and to determine the presence/absence of organic species resulting from reactions between the electrode, lithium ions and electrolyte, respectively.  相似文献   

20.
《Journal of power sources》2006,158(1):784-788
Carbon aerogel was prepared by the polycondensation of resorcinol (R) with formaldehyde (F), and sodium carbonate was added as a catalyst (C). Physical properties of carbon aerogel were characterized by infrared spectrometer (IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that carbon aerogel is an amorphous material with a pearly network structure, and it consists of one or two diffuse X-ray peaks. The results of cyclic voltammetry indicated that the specific capacitance of a carbon aerogel electrode in 6 M KOH electrolyte was approximately 110.06 F g−1. Through the galvanostatic charge/discharge measurement, it was found that the electrode is stable in KOH electrolyte, the maximum capacitance of the supercapacitor with carbon aerogel as the electrode active material was 28 F g−1. Besides, the supercapacitor has long cycle life. Thus, it was thought that the carbon aerogel is an excellent electrode material for a supercapcitor.  相似文献   

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