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1.
Pulverisation phenomena occurring during the charge/discharge cycling of metal hydride materials were studied by acoustic emission coupled to electrochemical measurements. Two kinds of materials were studied: a commercial LaNi5-based alloy and a ball-milled MgNi alloy. In both alloys, two populations of acoustic signals were detected during charging steps: P1, showing peak frequencies between 230 and 260 kHz, high energy and low rise time, and P2 with peak frequencies between 150 and 180 kHz, lower energy and longer rise time. Population P2 is related to the hydrogen evolution reaction whereas P1 is associated with pulverisation phenomena. No acoustic activity was detected during discharge. We also investigated pulverisation phenomena through cycles by monitoring the P1 population. It appears that pulverisation occurs mainly during the five first cycles for LaNi5 with a maximum at the second cycle, while pulverisation takes place all along the cycling for MgNi, but at a decreasing rate. By comparing the P1 activities, it appears that the pulverization phenomenon is less intensive on the MgNi electrode than on the LaNi5-based electrode.  相似文献   

2.
La0.60R0.20Mg0.20(NiCoMnAl)3.5 (R = La, Ce, Pr, Nd) alloys were prepared by inductive melting. Variations in phase structure and electrochemical properties due to partial replacement of La by Ce, Pr and Nd, were investigated. The alloys consist mainly of LaNi5 phase, La2Ni7 phase and LaNi3 phase as explored by XRD and SEM. The maximum discharge capacity decreases with Ce, Pr and Nd substitution for La. However, the cycling stability is improved by substituting Pr and Nd at La sites, capacity retention rate at the 100th cycle increases by 13.4% for the Nd-substituted alloy. The electrochemical kinetics measurements show that Ce and Pr substitution improves kinetics and thus ameliorates the high rate dischargeability (HRD) and low temperature dischargeability. The HRD at 1200 mA g−1 increases from 22.1% to 61.3% and the capacity at 233 K mounts up from 90 mAh g−1 to 220 mAh g−1 for the Ce-substituted alloy.  相似文献   

3.
MgTi, Mg0.5Ni0.5Ti and MgTi0.5Ni0.5 alloys doped with 10 wt.% Pd were prepared by high energy ball milling and evaluated as hydrogen storage electrodes for Ni-MH batteries. X-ray diffraction analyses indicated that the Mg0.5Ni0.5Ti and MgTi0.5Ni0.5 alloys could be monophased or composed of a nanoscale mixture of MgTi + NiTi and MgTi + MgNi phases, respectively. Their hydrogen storage characteristics were investigated electrochemically in KOH electrolyte. No activation step was observed during the cycling of the Mg-Ti-Ni electrodes in contrast to that observed with the MgTi electrode. The highest hydrogen discharge capacity was obtained with the MgTi0.5Ni0.5 electrode (536 mAh g−1) compared to 401 and 475 mAh g−1 for the Mg0.5Ni0.5Ti and MgTi electrodes, respectively. The ternary Mg-Ti-Ni alloys showed a better cycle life with an average capacity decay rate per cycle lower than 1.5% compared to ∼7% for the binary MgTi electrode. The Mg-Ni-Ti electrodes also displayed a much higher discharge rate capability than the binary MgTi electrode, especially with the Mg0.5Ni0.5Ti electrode. The origin of this was established on the basis of the anodic polarization curves, where a substantial decrease of the concentration overpotential (reflecting a higher hydrogen diffusivity) was observed for the Mg0.5Ni0.5Ti electrode.  相似文献   

4.
Nano-CuCo2O4 is synthesized by the low-temperature (400 °C) and cost-effective urea combustion method. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) studies establish that the compound possesses a spinel structure and nano-particle morphology (particle size (10–20 nm)). A slight amount of CuO is found as an impurity. Galvanostatic cycling of CuCo2O4 at 60 mA g−1 in the voltage range 0.005–3.0 V versus Li metal exhibits reversible cycling performance between 2 and 50 cycles with a small capacity fading of 2 mAh g−1 per cycle. Good rate capability is also found in the range 0.04–0.94C. Typical discharge and charge capacity values at the 20th cycle are 755(±10) mAh g−1 (∼6.9 mol of Li per mole of CuCo2O4) and 745(±10) mAh g−1 (∼6.8 mol of Li), respectively at a current of 60 mA g−1. The average discharge and charge potentials are ∼1.2 and ∼2.1 V, respectively. The underlying reaction mechanism is the redox reaction: Co ↔ CoO ↔ Co3O4 and Cu ↔ CuO aided by Li2O, after initial reaction with Li. The galvanostatic cycling studies are complemented by cyclic voltammetry (CV), ex situ TEM and SAED. The Li-cycling behaviour of nano-CuCo2O4 compares well with that of iso-structural nano-Co3O4 as reported in the literature.  相似文献   

5.
Polycrystalline samples of VOMoO4 are prepared by a solid-state reaction method and their electrochemical properties are examined in the voltage window 0.005–3 V versus lithium. The reaction mechanism of a VOMoO4 electrode for Li insertion/extraction is followed by ex situ X-ray diffraction analysis. During initial discharge, a large capacity (1280 mAh g−1) is observed and corresponds to the reaction of ∼10.3 Li. The ex situ XRD patterns indicate the formation of the crystalline phase Li4MoO5 during the initial stages of discharge, which transforms irreversibly to amorphous phases on further discharge to 0.005 V. On cycling, the reversible capacity is due to the extraction/insertion of lithium from the amorphous phases. A discharge capacity of 320 mAh g−1 is obtained after 80 cycles when cycling is performed at a current density of 120 mA g−1.  相似文献   

6.
Chemical lithiation with LiI in acetonitrile was performed for amorphous FePO4 synthesized from an equimolar aqueous suspension of iron powder and an aqueous solution of P2O5. An orthorhombic LiFePO4 olivine structure was obtained by annealing a chemically lithiated sample at 550 °C for 5 h in Ar atmosphere. The average particle size remained at approximately 250 nm even after annealing. The lithium content in the sample was quantitatively confirmed by Li atomic absorption analysis and 57Fe Mössbauer spectroscopy. While an amorphous FePO4/carbon composite cathode has a monotonously decreasing charge–discharge profile with a reversible capacity of more than 140 mAh g−1, the crystallized LiFePO4/carbon composite shows a 3.4 V plateau corresponding to a two-phase reaction. This means that the lithium in the chemically lithiated sample is electrochemically active. Both amorphous FePO4 and the chemically lithiated and annealed crystalline LiFePO4 cathode materials showed good cyclability (more than 140 mAh g−1 at the 40th cycle) and good discharge rate capability (more than 100 mAh g−1 at 5.0 mA cm−2). In addition, the fast-charge performance was found to be comparable to that with LiCoO2.  相似文献   

7.
Titanium oxides are an important class of lithium-ion battery electrodes owing to their good capacity and stability within the cell environment. Although most Ti(IV) oxides are poor electronic conductors, new methods developed to synthesize nanometer scale primary particles have achieved the higher rate capability needed for modern commercial applications. In this report, the anionic water stable titanium oxalate anion [TiO(C2O4)2]2− was isolated in high yield as the insoluble DABCO (1,4-diazabicyclo[2.2.2]octane) salt. Powder X-ray diffraction studies show that the titanium dioxide material isolated after annealing in air is initially amorphous, converts to N-doped anatase above 400 °C, then to rutile above 600 °C. Electrochemical studies indicate that the amorphous titanium dioxide phase within a carbon matrix has a stable cycling capacity of ∼350 mAh g−1. On crystallizing at 400 °C to a carbon-coated anatase the capacity drops to 210 mAh g−1, and finally upon carbon burn-off to 50 mAh g−1. Mixtures of the amorphous titanium dioxide and Li4Ti5O12 showed a similar electrochemical profile and capacity to Li4Ti5O12 but with the addition of a sloping region to the end of the discharge curve that could be advantageous for determining state-of-charge in systems using Li4Ti5O12.  相似文献   

8.
We present a two-step method to optimize the nanoporous characteristics of TiO2 samples thus enabling a higher charge and discharge capacity and a larger rate capability compared to dense TiO2 materials. We use a simple sol-gel process to fabricate spherical titanium glycolates precursors followed by subsequent hydrothermal or annealing treatments resulting, respectively, in highly porous or dense TiO2 nanospheres. These processes enable control of the grain size, pore structure, and specific surface area of the TiO2. The fabricated TiO2 nanostructures have been subsequently used to assemble lithium-ion batteries. Galvanostatic discharge-charge tests indicate that the porous TiO2 nanospheres possess high and stable reversible capacity of 229, 133, and 56 mAh g−1 at 0.06, 0.6 and 6 C, respectively; whereas the corresponding values for dense TiO2 nanospheres are 217, 45, and ∼1 mAh g−1. Such considerable improvement of the electrochemical activity is attributed to the porous TiO2 nanostructures, and subsequent change in diffusion length, and enables the possibility to optimize the high rate capability in TiO2-based lithium-ion batteries.  相似文献   

9.
LiMnPO4/C nanocomposites could be prepared by a combination of spray pyrolysis and wet ball-milling followed by heat treatment in the range of spray pyrolysis temperature from 200 to 500 °C. The ordered LiMnPO4 olivine structure without any impurity phase could be identified by X-ray diffraction analysis for all samples. It could be also confirmed from scanning electron microscopy and transmission electron microscopy observations that the final samples were the LiMnPO4/C nanocomposites with approximately 100 nm in primary particles size. The LiMnPO4/C nanocomposite samples were used as cathode active materials for lithium batteries, and the electrochemical tests were carried out for the cell Li|1 M LiPF6 in EC:DMC = 1:1|LiMnPO4/C at various charge/discharge rates in three charge modes. As a result, the final sample which was synthesized at 300 °C by spray pyrolysis showed the best electrochemical performance due to the largest specific surface area, the smallest primary particle size and a well distribution of carbon. At galvanostatic charge/discharge rates of 0.05 C, the cell delivered first discharge capacities of 123 and 165 mAh g−1 in correspondence to charge cutoff voltages of 4.4 and 5.0 V, respectively. Furthermore, in a constant current-constant voltage charge mode at 4.4 V, the cells also exhibited initial discharge capacities of 147 mAh g−1 at 0.05 C, 145 mAh g−1 at 0.1 C, 123 mAh g−1 at 1 C and 65 mAh g−1 at 10 C. Moreover, the cells showed fair good cycleability over 100 cycles.  相似文献   

10.
One-dimensional (1D) vanadium pentoxide (V2O5) nanofibers (VNF) are synthesized by electrospinning vanadium sol-gel precursors containing vanadyl acetylacetonate and poly(vinylpyrrolidone) followed by sintering. Crystal structure, molecular structure and morphology of electrospun VNF are analyzed using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area diffraction (SAED), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Single-phase electrospun VNF ∼300-800 nm in diameter, 20-50 μm long (aspect ratio > 50) with porous interconnected fibrous morphology are revealed by FESEM and TEM analysis. Electrochemical properties of the sintered VNF, as a cathode in lithium-ion batteries, explored using cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) give rise to new understandings of the electrochemical processes occurring in these nanofibrous cathodes. Electrospun VNF exhibits initial discharge capacity ∼316 mAh g−1 (∼2.2 Li per V2O5) in the voltage range of 1.75 and 4.0 V vs. Li/Li+ at 0.1 C rate. When cycled at a reduced voltage range of 2.0-4.0 V vs. Li/Li+, less phase transitions occur, giving rise to the initial specific capacity of 308 mAh g−1 and improved cyclic retention of 74% after 50 cycles.  相似文献   

11.
We present an electrochemical study of BiSbO4, an opened layered oxide having a structure related to Aurivillius phases. Li//BiSbO4 cells show a large specific capacity as high as 1250 mAh g−1 during reduction down to 0.5 V. This reaction involves 18Li atoms per formula unit, pointing it towards a very promising cathode material for primary lithium batteries, in particular for ICD devices. The characterization of the reduction products indicates that the reduction of BiSbO4 with lithium presumably goes along firstly with the formation of metallic Sb and Bi to follow the formation of the alloys Li3Bi and Li3Sb dispersed in a lithium oxide matrix. In situ X-ray diffraction experiments proved the amorphous nature of both metals and final alloys. On the other hand when Li//BiSbO4 cells are limited to discharge down to 1.2 V, BiSbO4 reacts with 5Li atoms. After the first discharge, that develops a specific capacity of 350 mAh g−1, high cyclability has been observed.  相似文献   

12.
A composite anode materials was prepared that contained tin compounds of Sn6O4(OH)4, SnO2 and Sn3PO4 on the surface of carbonaceous mixture mesophase graphite particles (MGP) and nature graphite (NG). The nanosize tin compounds were electrolessly plated from aqueous solutions onto the carbonaceous mixture. The morphology and structure of tin compounds were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the tin compounds particle size was a crucial factor to improve Sn compounds/Carbon composite anodes for cyclability and reversible capacity. The homogeneous dispersion and smaller particle size of tin compounds was attributed to the additive of NG. As the carbonaceous substrate was C-C mixture carbon, the particle size of Sn compounds was about 20-30 nm. However, the particle size was 100-200 nm, as the carbon substrate was singular MGP. Electrochemical performance test of the Sn compounds/C-C composite electrode shows the maximum specific charge capacity of 583 mAh g−1 at the 5th cycle. The charge capacity retention of Sn compounds/C-C electrode was 85% after 20 cycles. The reversible capacity of Sn compounds/C-C electrode increased 292 and 97 mAh g−1 more than pristine (NG + MGP) electrode and Sn compounds/C electrode at the 5th cycle, respectively.  相似文献   

13.
Mg-Ti-H alloys were synthesized by high energy ball milling from equimolar mixtures of MgH2 + TiH2, MgH2 + Ti and Mg + TiH2 in the presence of 10 wt.% Pd. X-ray diffraction analyses combined with Rietveld refinement revealed that after 60 h of milling, all as-milled Mg-Ti-H alloys are made of two face-centered-cubic (fcc) phases, with lattice parameters ∼4.47 and ∼4.25 Å, in different proportions depending on the composition of the initial mixture. The Mg-Ti-H alloys displayed a similar electrochemical behavior, i.e. their hydrogen discharge capacity was highest during the first cycle and then decreased rapidly with cycling. The maximum discharge capacities of the 60 h-milled MgH2 + TiH2, MgH2 + Ti and Mg + TiH2 materials were 300, 443 and 454 mAh g−1, respectively. No apparent correlation could be established between the maximum discharge capacity of the Mg-Ti-H materials and the two fcc phase proportion.  相似文献   

14.
Monoclinic Li3V2(PO4)3 can be rapidly synthesized at 750 °C for 5 min (MW5m) by using temperature-controlled microwave solid-state synthesis method (TCMS). The carbon-free sample MW5m presents well electrochemical properties. In the cut-off voltage 3.0-4.3, MW5m presents a charge capacity 132 mAh g−1, almost equivalent to the reversible cycling of two lithium ions per Li3V2(PO4)3 formula unit (133 mAh g−1), and discharge capacity 126.4 mAh g−1. In the cut-off voltage 3.0-4.8 V, MW5m shows an initial discharge capacity of 183.4 mAh g−1, near to the theoretical discharge capacity. In the cycle performance, the capacity fade of Li3V2(PO4)3 is dependent on the cut-off voltage and the preparation method.  相似文献   

15.
The comparison of the rate capability of LiCr0.2Ni0.4Mn1.4O4 spinels synthesized by the sucrose aided combustion method at 900, 950 and 1000 °C is presented. XRD and TEM studies show that the spinel cubic structure remains unchanged on heating but the particle size is notably modified. Indeed, it increases from 695 nm at 900 °C to 1465 nm at 1000 °C. The electrochemical properties have been evaluated by galvanostatic cycling at 25 and 55 °C between 1 C and 60 C discharge rates. At both temperatures, all samples exhibit high working voltage (∼4.7 V), elevated capacity (∼140 mAh g−1) and high cyclability (capacity retention ∼99% after 50 cycles even at 55 °C). The samples also have huge rate capability. They retain more than 70% of their maximum capacity at the very fast rate of 60 C. The effect of the particle size on the rate capability at 25 and at 55 °C has been investigated. It was demonstrated that LiCr0.2Ni0.4Mn1.4O4 annealed at 900 °C, with the lowest particle size, has the best electrochemical performances. In fact, among the LiNi0.5Mn1.5O4-based cathodes, SAC900 exhibits the highest rate capability ever published. This spinel, able to deliver 31,000 W kg−1 at 25 °C and 27,500 W kg−1 at 55 °C is a really promising cathode for high-power Li-ion battery.  相似文献   

16.
A novel polymer electrolyte based on triblock copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) with ionically active SiO2 inclusions has been designed. The electrolyte shows favorable features for ion migration such as low glass transition temperature and high concentration of amorphous phase. Combined with the effect of active SiO2, its ionic conductivity is about 8.0 × 10−5 S cm−1 at 30 °C, which exceeds that for the PEO-based systems. As applying them to cells with LiFePO4-type cathodes, a capacity of about 147.0 mAh g−1 is obtained at 60 °C, which is retained by more than 90% after 40 charge/discharge cycles. Moreover, about 100 mAh g−1 could still be delivered as temperature decreases to 30 °C.  相似文献   

17.
The pulverization of amorphous MgNi, Mg0.9Ti0.1Ni and Mg0.9Ti0.1NiAl0.05 materials prepared by mechanical alloying was evaluated by acoustic emission (AE) measurements during their electrochemical hydriding. It was confirmed that the pulverization of MgNi-based electrode occurs mostly at the end of the charge when the hydrogen evolution reaction is initiated. On the basis of the AE activity measurements, the positive influence of the Ti substitution and Al addition on the MgNi-based alloy pulverization resistance is demonstrated. This is mainly attributed to the lower porosity of these materials, limiting the accumulation of H2 bubbles in the agglomerate pores. Combined with a better corrosion resistance, this characteristic produces an improvement of the cycle life of the MH electrodes. It was also shown that the AE energy distribution can be described by the Gutenberg–Richter relationship. The AE energy is higher for cracking related to the volume expansion than for the pulverization associated with the formation of H2 bubbles in the agglomerate pores. Ti substitution and Al addition also induce a larger proportion of high-energy AE signals.  相似文献   

18.
Nanostructured Fe3O4 nanoparticles were prepared by a simple sonication assisted co-precipitation method. Transmission electron microscopy, X-ray diffraction and BET surface area analysis confirmed the formation of ∼20 nm crystallites that constitute ∼200 nm nanoclusters. Galvanostatic charge-discharge cycling of the Fe3O4 nanoaprticles in half cell configuration with Li at 100 mA g−1 current density exhibited specific reversible capacity of 1000 mAh g−1. The cells showed stability at high current charge-discharge rates of 4000 mA g−1 and very good capacity retention up to 200 cycles. After multiple high current cycling regimes, the cell always recovered to full reversible capacity of ∼1000 mAh g−1 at 0.1 C rate.  相似文献   

19.
We report a simple strategy to prepare a hybrid of lithium titanate (Li4Ti5O12, LTO) nanoparticles well-dispersed on electrical conductive graphene nanosheets as an anode material for high rate lithium ion batteries. Lithium ion transport is facilitated by making pure phase Li4Ti5O12 particles in a nanosize to shorten the ion transport path. Electron transport is improved by forming a conductive graphene network throughout the insulating Li4Ti5O12 nanoparticles. The charge transfer resistance at the particle/electrolyte interface is reduced from 53.9 Ω to 36.2 Ω and the peak currents measured by a cyclic voltammogram are increased at each scan rate. The difference between charge and discharge plateau potentials becomes much smaller at all discharge rates because of lowered polarization. With 5 wt.% graphene, the hybrid materials deliver a specific capacity of 122 mAh g−1 even at a very high charge/discharge rate of 30 C and exhibit an excellent cycling performance, with the first discharge capacity of 132.2 mAh g−1 and less than 6% discharge capacity loss over 300 cycles at 20 C. The outstanding electrochemical performance and acceptable initial columbic efficiency of the nano-Li4Ti5O12/graphene hybrid with 5 wt.% graphene make it a promising anode material for high rate lithium ion batteries.  相似文献   

20.
Hybrid microwave synthesis has been applied for preparation of Li4Ti5O12, Li2Ti3O7, Li2TiO3 and LiTiO2 for the first time. Stepwise heating was used for avoiding the instantaneous release of gas by-product and obtaining well-shaped samples. The samples were characterized by powder X-ray diffraction, energy-dispersive X-ray analysis and scanning electron microscopy. The obtained samples have relatively uniform particle sizes. The electrochemical performance of Li4Ti5O12 and Li2Ti3O7 were investigated. The first discharge capacity of Li4Ti5O12 was 150 mAh g−1 and 141 mAh g−1 after 27 cycles and a very flat discharge and charge curve of Li4Ti5O12 was shown at about 1.56 V. Similarly, Li2Ti3O7 exhibits good cycle performance. The initial discharge capacity is 118 mAh g−1 and 30th cycle is still 112 mAh g−1.  相似文献   

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