107,499 research outputs found
Structural and electrochemical characterization of xLi[Li1/3Mn2/3]O2·(1 - x)Li[Ni1/3Mn1/3Co1/3]O2 (0 ≤ x ≤ 0.9) as cathode materials for lithium ion batteries
No full textA series of cathode materials with molecular notation of xLi[Li1/3Mn2/3]O2·(1 - x)Li[Ni1/3Mn1/3Co1/3]O2 (0 ≤ x ≤ 0.9) were synthesized by combination of co-precipitation and solid state calcination method. The prepared materials were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques, and their electrochemical performances were investigated. The results showed that sample 0.6Li[Li1/3Mn2/3]O2·0.4Li[Ni1/3Mn1/3Co1/3]O2 (x = 0.6) delivers the highest capacity and shows good capacity-retention, which delivers a capacity ∼250 mAh g-1 between 2.0 and 4.8 V at 18 mA g-1. © 2008 Elsevier B.V. All rights reserved
The effects of TiO2 coating on the electrochemical performance of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode material for lithium-ion battery
No full textTiO2-coated Li[Li0.2Mn0.54Ni0.13Co0.13]O2 materials have been synthesized and investigated as cathode materials for lithium-ion batteries at both 25 °C and elevated temperature (55 °C). The structure and morphology of the coated samples were characterized and compared. The XRD results indicate that lattice parameters of the materials did not change distinctly after surface coating. The SEM images demonstrate that the surface of Li[Li0.2Mn0.54Ni0.13Co0.13]O2 samples were covered with nano-sized TiO2 particles. Differential scanning calorimetry (DSC) analysis results show that thermal stability of the materials was improved. It is also shown that the irreversible capacity loss of the materials was obviously reduced and their capacity retention behaviour was improved after surface modification. © 2008 Elsevier B.V. All rights reserved
The effects of sintering temperature and time on the structure and electrochemical performance of LiNi0.8Co0.2O2 cathode materials derived from sol-gel method
No full textLiNi0.8Co0.2O2 cathode materials were synthesized by the sol-gel method using citric acid as a chelating agent. The effects of sintering temperature and time on the structure and electrochemical performance of the materials were investigated. The materials were characterized by X-ray diffraction, together with refinement analysis by the Rietveld method. The results showed that sintering temperature and time had significant influence on the structure of the materials. The lattice parameters (a, c, c/a and volume) and the amount of Ni in the Li 3a site showed a peak shape change with sintering temperature and time. The sample sintering at 998 K for 24 h showed the best ordering layered structure with the maximum c/a ratio and the least amount of Ni on the Li 3a site. The charge-discharge experiments also indicated that the sample had the best electrochemical properties, with an initial capacity of 181 mA h/g and a capacity retention of 82.9% after 50 cycles at a 0.1 C rate between 3.0 V and 4.2 V. In addition, the compositional homogeneity of these cathode materials derived using the sol-gel method was demonstrated by scanning electron microscopy/energy dispersive analysis
Mechanisms for surface potential decay on fluorinated epoxy in high voltage DC applications
Full text linkEpoxy resin has been extensively used for decades as an insulation material in high voltage transmission systems. However, this insulation material does suffer from bulk and surface charging when used as insulating spacer, mainly in high voltage DC applications. By applying fluorination treatment, the surface of polymeric insulation is chemically treated and so modifies charge transport characteristics of the material. In doing so, excellent surface properties can be obtained without compromising the bulk characteristics of the polymeric insulation. In this paper, the authors investigate the surface potential decay performance of non-fluorinated and fluorinated epoxy resin samples. The surface decay performance of insulating material is a crucial parameter in dissipating accumulation of surface and bulk charge that can lead to premature breakdown of the insulating material. The epoxy samples were characterised by Energy Dispersive X-Ray (EDX) analysis to determine the changes in chemical composition of the samples before and after fluorination treatment. Surface potential decay measurement using positive corona discharging was then performed, followed by bulk DC conductivity measurement to further explain the mechanisms which govern the surface potential decay. The existence of surface-fluorinated layer on the treated samples had been found to play a major role in dictating the movement of charges away from the surface during the decay process. The influence of fluorination treatment on the decay mechanisms was discussed
The use of external fixation for the management of acute and chronic Monteggia fractures in children
No full textPurpose The main objective of this study was to retrospectively evaluate the clinical and radiological outcomes of acute (AMF) and chronic Monteggia fractures (CMF) in children treated by closed or open reduction and external fixation (EF). Methods This is a retrospective review of 26 patients with Monteggia fracture. Patients with AMF (time between trauma and surgery less than two weeks) were treated by closed reduction and EF of the ulna (Group A; 15 patients) while those with CMF (time between trauma and surgery more than three weeks) were managed by closed or open reduction and EF of the ulna (Group B; 11 patients). Clinical outcome was evaluated with radiography and the short version of the Disabilities of the Arm, Shoulder and Hand outcome questionnaire (Quick DASH). Complications were recorded in both groups. Results No secondary displacement, wire migration, consolidation delays, nonunion, malunion or re-fracture was noted. However, one patient in Group A (6.7%) developed heterotopic ossification of the ulna; the final functional outcome was good (Quick DASH score: 18.2). One case of postoperative redislocation of the radial head was detected in Group B (9.1%). Two patients (7.6%) developed transient pin tract infection. Despite the fact that 16 out of 26 patients (six in Group A and ten in Group B) complained of the clinical appearance and/or had intermittent residual pain on the injured side, the results were essentially the same between the two groups of patients (p > 0.05). Conclusion EF is an alternative for the management of acute and chronic paediatric Monteggia fractures. It provides satisfactory radiological and clinical outcomes with relatively low rates of complications
Vinyl ethylene sulfite as a new additive in propylene carbonate-based electrolyte for lithium ion batteries
No full textVinyl ethylene sulfite (VES) is studied as a new additive in propylene carbonate (PC)-based electrolyte for lithium ion batteries. The electrochemical results show that the artificial graphite material exhibits excellent electrochemical performance in a PC-based electrolyte with the addition of the proper amount of VES. According to our spectroscopic results, VES is reduced to ROSO2Li (R=C4H6), Li2SO3 and butadiene (C4H6) through an electrochemical process which precedes the decomposition of PC. Furthermore, some of the Li 2SO3 could be further reduced to Li2S and Li2O. All of these products are proven to be components of the solid electrolyte interface (SEI) layer. © 2009 The Royal Society of Chemistry
Study on the elastic-plastic behavior of a porous hierarchical bioscaffold used for bone regeneration
No full textA perfectly plastic von Mises model is proposed to study the elastic-plastic behavior of a porous hierarchical scaffold used for bone regeneration. The proposed constitutive model is implemented in a finite element (FE) routine to obtain the stress-strain relationship of a uniaxially loaded cube of the scaffold, whose constituent is considered to be composed of cortical bone. The results agree well with experimental data for uniaxial loading case of a cancellous bone. We find that the unhomogenized stress distribution results in different mechanical properties from but still comparable to our previous theory. The scaffold is a promising candidate for bone regeneration
Designing 3D Biomorphic Nitrogen-Doped MoSe2/Graphene Composites toward High-Performance Potassium-Ion Capacitors
No full textPotassium-ion hybrid capacitors (KICs) reconciling the advantages of batteries and supercapacitors have stimulated growing attention for practical energy storage because of the high abundance and low cost of potassium sources. Nevertheless, daunting challenge remains for developing high-performance potassium accommodation materials due to the large radius of potassium ions. Molybdenum diselenide (MoSe2) has recently been recognized as a promising anode material for potassium-ion batteries, achieving high capacity and favorable cycling stability. However, KICs based on MoSe2 are scarcely demonstrated by far. Herein, a diatomite-templated synthetic strategy is devised to fabricate nitrogen-doped MoSe2/graphene (N-MoSe2/G) composites with favorable pseudocapacitive potassium storage targeting a superior anode material for KICs. Benefiting from the unique biomorphic structure, high electron/K-ion conductivity, enriched active sites, and the conspicuous pseudocapacitive effect of N-MoSe2/G, thus-derived KIC full-cell manifests high energy/power densities (maximum 119 Wh kg−1/7212 W kg−1), outperforming those of recently reported KIC counterparts. Furthermore, the potassium storage mechanism of N-MoSe2/G composite is systematically explored with the aid of first-principles calculations in combination of in situ X-ray diffraction and ex situ Raman spectroscopy/transmission electron microscopy/X-ray photoelectron spectroscopy
- …
