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941.
We present transfer length method measurements of the contact resistance between Cu and graphene, and a method to significantly reduce the contact resistance by vacuum annealing. Even in samples with heavily contaminated contacts, the contacts display very low contact resistance post annealing. Due to the common use of Cu, and its low chemical reactivity with graphene, thermal annealing will be important for future graphene devices requiring non-perturbing contacts with low contact resistance. 相似文献
942.
Hirokazu KitauraAkitoshi Hayashi Kiyoharu TadanagaMasahiro Tatsumisago 《Solid State Ionics》2011,192(1):304-307
To improve the electrochemical performance of an all-solid-state In/80Li2S⋅20P2S5 (electrolyte)/LiMn2O4 cell, a lithium-titanate thin film was used to coat LiMn2O4. The interfacial resistance between LiMn2O4 and the electrolyte (measured after initial charging) decreased when the LiMn2O4 particles were coated with lithium-titanate. A cell with lithium-titanate-coated LiMn2O4 had a higher capacity than a cell with noncoated LiMn2O4 for current densities in the range 0.064 to 2.6 mA cm− 2. Additionally, a cell with coated LiMn2O4 retained 96% of the 10th-cycle reversible capacity at a current density of 0.064 mA cm− 2 after 50 cycles. 相似文献
943.
We study a rechargeable lithium-ion battery that uses a many-particle FePO4 electrode to reversibly store lithium atoms. This process is accompanied by a phase transition and charging/discharging run along different paths, so that hysteretic behavior is observed.Although there are experimental studies suggesting that the overall behavior of the battery is a many-particle effect, most authors exclusively describe the phase transition within a single particle model of the electrode.In this work, we study in detail a many-particle model for the electrode. The model is capable to describe a kind of phase transition where each individual particle of the electrode is homogeneous. It will be shown that the particles are either in the first phase or in the second phase. This phenomenon is due to the non-monotone relation between the chemical potential and the lithium mole fraction of a single particle.The pressure-radius relation of a spherical elastic rubber balloon also exhibits non-monotone behavior. In fact, a system of many interconnected balloons behaves correspondingly to an electrode consisting of many storage particles. The analogy between the two systems is important, because the predictions of the many-particle model can easily be tested with rubber balloons of macroscopic size than with an ensemble of microscopically small (FePO4) particles. 相似文献
944.
Experimental investigations on a sodium ion conducting gel polymer electrolyte nanocomposite based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), dispersed with silica nanoparticles are reported. The gel nanocomposites have been obtained in the form of dimensionally stable, transparent and free-standing thick films. Physical characterization by X-ray diffraction (XRD), Fourier transform Infra-red (FTIR) spectroscopy and Scanning electron microscopy (SEM) have been performed to study the structural changes and the ion-filler-polymer interactions due to the dispersion of SiO2 nanoparticles in gel electrolytes. The highest ionic conductivity of the electrolyte has been observed to be 4.1 × 10−3 S cm− 1 at room temperature with ~ 3 wt.% of SiO2 particles. The temperature dependence of the ionic conductivity has been found to be consistent with Vogel-Tammen-Fulcher (VTF) relationship in the temperature range from 40 to 70 °C. The sodium ion conduction in the gel electrolyte film is confirmed from the cyclic voltammetry, impedance analysis and transport number measurements. The value of sodium ion transport number (tNa+) of the gel electrolyte is significantly enhanced to a maximum value of 0.52 on the 15 wt.% SiO2 dispersion. The physical and electrochemical analyses indicate the suitability of the gel electrolyte films in the sodium batteries. A prototype sodium-sulfur battery, fabricated using optimized gel electrolyte, offers the first discharge capacity of ~165 mAh g− 1 of sulfur. 相似文献
945.
γ-Fe2O3 has a spinel structure with cation vacancy and is expected to perform as a favorable electrode material for secondary lithium-ion battery. When lithium is inserted electrochemically into γ-Fe2O3, prolonged potential change is observed after the insertion. In this study, we inserted various amount of Li into γ-Fe2O3 (x = 0.66, 1.1, 1.5 in terms of LiXFe2O3), then made the circuit open, measured X-ray diffraction (XRD) patterns at various elapsed time, and analyzed the crystal structure change of γ-Fe2O3 with time by the Rietveld method. The X-ray Rietveld analysis revealed that the iron occupancy of 8a site decreased and that of 16c site increased with lithium insertion process and after lithium insertion, the iron occupancy of 8a site increased and that of 16c site decreased gradually with relaxation time. It is indicated that lithium prefer 8a site to occupy kinetically, on the other hand, prefer 16c site thermodynamically. 相似文献
946.
A. Tóth M. VeresK. Kereszturi M. MohaiI. Bertóti J. Szépvölgyi 《Applied Surface Science》2011,257(24):10815-10820
The surfaces of untreated and helium plasma-based ion implantation (He PBII) treated poly(ethylene terephthalate) (PET) samples were characterised by reflectance colorimetry, contact angle studies and measurements of surface electrical resistance. The results were related to the structural and compositional data obtained by the authors earlier on parallel samples by XPS and Raman spectroscopy. Inverse correlations between lightness and ID/IG ratio and between chroma and ID/IG ratio were obtained, suggesting that the PBII-treated PET samples darken and their colourfulness decreases with the increase of the portion of aromatic sp2 carbon rings in the chemical structure of the modified layer. Direct correlation between water contact angle and the ID/IG ratio and inverse correlations between surface energy and ID/IG ratio and between dispersive component of surface energy and ID/IG ratio were found, reflecting that surface wettability, surface energy and its dispersive component decrease with the formation of surface structure, characterised again by enhanced portion of aromatic sp2 carbon rings. The surface electrical resistance decreased with the increase of the surface C-content determined by XPS and also with the increase of the surface concentration of conjugated double bonds, reflected by the increase of the π → π* shake-up satellite of the C 1s peak. 相似文献
947.
Pengfei Chui Kangning Sun Chang Sun Xiuqing Yang Ting Shan 《Applied Surface Science》2011,257(15):6787-6791
A nanostructured layer was fabricated by using fast multiple rotation rolling (FMRR) on the surface of 316L stainless steel. The microstructure in the surface was characterized by transmission electron microscopy and X-ray diffraction. The effects of FMRR on the microhardness, surface roughness and corrosion behavior of the stainless steel were investigated by microhardness measurements, surface roughness measurements, potentiodynamic polarization curves and pitting corrosion tests. The surface morphologies of pitting corrosion specimens were characterized by scanning electron microscopy. The results show that FMRR can cause surface nanocrystallization with the grain size ranges from 6 to 24 nm in the top surface layer of the sample. The microhardness of FMRR specimen in the top surface layer remarkably increases from 190 to 530 HV. However, the surface roughness slightly rises after FMRR treatment. The potentiodynamic polarization curves and pitting corrosion tests indicated that the FMRR treated 316L stainless steel with a surface nanocrystallized layer reduced the corrosion resistance in a 3.5% NaCl solution and enhanced the pitting corrosion rate in a FeCl3 solution. Possible reasons leading to the decrease in corrosion resistance were discussed. 相似文献
948.
Nanoscopic impedance measurements were carried out on silver ion conducting glasses by coupling an impedance spectrometer with an atomic force microscope. When ac voltages were applied to a conducting AFM tip being in contact with the glass surface, silver nanoparticles were formed during the cathodic half cycle, which were not completely reoxidized in the anodic half cycle. We describe two protocols allowing for a controlled particle growth. The electrochemical oxidation/reduction processes led to low tip/sample interfacial impedances, and the formed silver particles acted as nanoelectrodes sensing the spreading resistance of the glass below the particles. We made a quantitative check of the spreading resistance formula under the assumption that spreading of the electric field is governed by the lateral diameter of the particles and found good agreement between the mean value of the local conductivities obtained at different tip positions and the macroscopic conductivity. 相似文献
949.
Micrometric LiMn2O4 particles are mechano-chemically modified by ball-milling to obtain a mixture of nano- and micro-scale particles. This mixture is tested as a potential active cathode material for rapid-charge Li ion batteries, and also as a model system for studying the detailed kinetics of Li intercalation/de-intercalation in such electrodes. Ragone plots recorded using galvanostatic measurements indicate enhanced power delivery characteristics of the ball-milled LiMn2O4 compared to its unprocessed counterpart. The processed material also exhibits improved resistance against electrolyte reactions and surface film formation. Due to these advantageous electrochemical attributes, the ball-milled LiMn2O4 serves as an adequately suited system for exploring certain fundamental aspects of Li intercalation in this material. Scan rate dependent slow scan cyclic voltammetry helps to identify the kinetic and diffusion controlled features of Li transport in mechano-chemically processed LiMn2O4. Electrochemical impedance spectroscopy substantiates these findings further and provides detailed kinetic parameters, including voltage dependent charge transfer resistance and diffusion coefficient of Li transport. 相似文献
950.
A fabrication of all-solid-state thin-film rechargeable lithium ion batteries by sol-gel method is expected to achieve both the simplification and cost reduction for fabrication process. TiO2 thin film electrode was prepared by PVP (polyvinylpyrrolidone) sol-gel method combined with spin-coating on Li1 + xAlxGe2 − x(PO4)3 (LAGP) solid electrolyte which has wide electrochemical window. The thin film was composed of anatase TiO2 that is the most active phase for Li insertion and extraction and contacted well with LAGP substrate. In the cyclic voltammogram, a redox couple was observed at 1.8 V vs. Li/Li+ assigned to Li insertion/extraction into/from anatase TiO2, indicating that the thin film worked as electrode for lithium battery. The charge and discharge test in various charge and discharge rates revealed that the discharge process (delithiation) is thought to be faster than charge process (lithiation). It is attested that the sol-gel process, which derives both simplification and cost reduction for fabrication process, can be applied to thin film battery using LAGP solid electrolyte. 相似文献