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Sb–C nanofibers are synthesized successfully through a single-nozzle electrospinning technique and subsequent calcination. The structural and morphological characterizations reveal the uniform nanofiber structure with the Sb nanoparticles embedded homogeneously in the carbon nanofibers. Electrochemical experiments show that the Sb–C nanofiber electrode can deliver large reversible capacity (631 mA h g−1) at C/15, greatly improved rate capability (337 mA h g−1 at 5 C) and excellent cycling stability (90% capacity retention after 400 cycles). The superior electrochemical performances of the Sb–C nanofibers are due to the unique nanofiber structure and uniform distribution of Sb nanoparticles in carbon matrix, which provides a conductive and buffering matrix for effective release of mechanical stress caused by Na ion insertion/extraction and prevent the aggregation of the Sb nanoparticles.
Publisher Summary Multiple dual-mode phones are on the market based on different operating systems. Linux, Symbian, the proprietary Research in Motion (RIM) Blackberry, Google Android, and Windows Mobile are the most popular. All the devices come with a “native” dialer that has been carrier certified, but these do not support any unbounded mobile communications (UMC) functionality and are strictly cellular service products. Other products may now offer a SIP softphone, but it is not integrated into the “native” dialer and is severely limited in functionality. With the existing crop of commercially available dual-mode phones, any UMC functionality has to be delivered as an adjunct application. Without direct collaboration with the handset manufacturer or OS provider (Microsoft or Nokia), supplanting the native dialer with a UMC solution is not without its problems. For both Microsoft Windows Mobile-based and Symbian-based devices, the native dialer functionality is built into the OS structure and cannot be treated as a user application. For that reason, any UMC application must be designed to work collaboratively with the native dialer. Even in the best scenarios, there are behaviors that are not optimum.
The thermal and electrochemical properties of polyurethane electrolyte/carbon black composites have been studied. The material structure presented amorphous features and the electrical response was described in terms of equivalent circuits accounting for the different relaxation processes occurring in the medium. The conductivity behavior did not fit satisfactorily either the effective medium theory or conventional percolation models. Flexible electrochemical capacitors using the composite as active material in association with large area collectors have been built and tested. The performance of the capacitors were characterized by a variety of electrochemical techniques, including impedance spectroscopy, cyclic voltammetry, galvanostatic charge–discharge methods, and long term cycling tests. The device prepared with composite electrodes containing 20 wt% of carbon black exhibited a capacity of 0.7 F cm−3 under 2 V providing an energy density of 0.4 W h l−1.
A highly efficient thermal strategy to manage a high-powered Li-ion battery package within the required safe temperature range is of great demand for electric vehicles (EVs) applications. A sandwiched cooling structure using copper metal foam saturated with phase change materials was designed. The thermal efficiency of the system was experimentally evaluated and compared with two control cases: a cooling mode with pure phase change materials and an air-cooling mode. The results showed that the thermal management with air natural convection cannot fulfill the safety demand of the Li-ion battery. The use of pure PCM can dramatically reduce the surface temperature and maintain the temperature within an allowable range due to the latent heat absorption and the natural convection of the melted PCM during the melting process. The foam-paraffin composite further reduced the battery's surface temperature and improved the uniformity of the temperature distribution caused by the improvement of the effective thermal conductivity. Additionally, the battery surface temperature increased with an increase in the porosity and the pore density of the metal foam.
A facile route for the synthesis of ZnSe-reduced graphene oxide (rGO) nanocomposites is reported. The ZnSe nanoparticles with irregular shapes are ∼40nm in size and anchored on graphene nanosheets. As the electrode material for lithium ion batteries (LIBs), the ZnSe-rGO nanocomposites exhibit better electrochemical performances than the bare ZnSe. The nanocomposites demonstrate high reversible capacity of 876mAhg−1 at 100mAg−1 after 50 cycles, outstanding cyclic performance and excellent rate capability (778mAhg−1 even after 400 cycles at 1000mAg−1 with nearly 100% coulombic efficiency). The improvement in Li-storage properties of ZnSe-rGO is attributed to the synergetic effects between ZnSe nanoparticles and graphene nanosheets. The unique structure restrains the aggregation of ZnSe nanoparticles and graphene nanosheets to some extent, improves the conductivity of nanocomposites, buffers the volume changes of ZnSe nanoparticles during the conversion reactions, and provides more exposed available surfaces for Li-storage. The excellent electrochemical properties reveal ZnSe-rGO nanocomposite is a promising candidate as electrode materials for LIBs applications.
The effectiveness of well-known electrolyte additives singly or in combination on LiCoO2/graphite pouch cells has been systematically investigated and compared using the ultra high precision charger (UHPC) at Dalhousie University and electrochemical impedance spectroscopy (EIS). UHPC studies are believed to identify the best electrolyte additives singly or in combination within a short time period (several weeks). Three parameters: 1) the coulombic efficiency (CE); 2) the charge endpoint capacity slippage (slippage) and 3) the charge transfer resistance (R ct), of LiCoO2/graphite pouch cells with different electrolyte additives singly or in combination were measured and the results for over 55 additive sets are compared. The experimental results suggest that a combination of electrolyte additives can be more effective than a single electrolyte additive. However, of all the additive sets tested, simply using 2 wt.% vinylene carbonate yielded cells very competitive in CE, slippage and R ct. It is hoped that this comprehensive report can be used as a guide and reference for the study of other electrolyte additives singly or in combination.
Routing for wireless sensor networks based on gradient is a simple, reliable solution resulting in low information costs for the network package, as well as for the node itself. It is used for convergent traffic, where sensor nodes send messages to the sink node. Due to message transmission failures inherent to wireless sensor networks, researches in this area agree that point-to-point message confirmation in these networks is essential. This work proposes solutions for gradient-based routing using a confirmation mechanism for different neighbors, where four protocol variations are evaluated for sensor networks applications in order to monitor and control electrical variables. Results demonstrate that the protocol based on the longest distance has a satisfactory package delivery rate in severe conditions specified to the application. Furthermore, results show in which situations each routing protocol variation better suits the target application.
Much has been said about the high-energy, long-lasting potential of Li metal batteries, and yet little has been demonstrated at the cell scale. Here, Jun Liu and colleagues demonstrate a Li metal pouch cell with a 300 Wh kg−1 energy density and a 200-cycle lifetime.
LiNi0.33−x Mn0.33Co0.33Y x O2 materials are synthesized by Y3+ substitute of Ni2+ to improve the cycling performance and rate capability. The influence of the Y3+ doping on the structure and electrochemical properties are investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and galvanostatic charge/discharge tests. LiNi0.33Mn0.33Co0.33O2 exhibits the capacity retentions of 89.9 and 87.8% at 2.0 and 4.0C after 40 cycles, respectively. After doping, the capacity retentions of LiNi0.305Mn0.33Co0.33Y0.025O2 are increased to 97.2 and 95.9% at 2.0 and 4.0C, respectively. The discharge capacity of LiNi0.305Mn0.33Co0.33Y0.025O2 at 5.0C remains 75.7% of the discharge capacity at 0.2C, while that of LiNi0.33Mn0.33Co0.33O2 is only 47.5%. EIS measurement indicates that LiNi0.305Mn0.33Co0.33Y0.025O2 electrode has the lower impedance value during cycling. It is considered that the higher capacity retention and superior rate capability of Y-doped samples can be ascribed to the reduced surface film resistance and charge transfer resistance of the electrode during cycling.
The effect of the solvent used in the chemical polymerization of pyrrole on the electrochemical pseudo-capacitance properties of the material is investigated by means of cyclic voltammetry. Electro-conducting polypyrroles (PPy) are prepared in the presence of various solutions such as H2O, diethyl ether, and acetonitrile (ACN). The PPy powder prepared in H2O exhibits the largest capacitance value, approximately 355 Fg−1, in ACN solution containing 1M tetraethylammonium tetrafluoroborate (TEABF4). This dependency on solvent is directly related to the surface roughness of PPy powder.
The competition of Na+ ion versus K+ ion transport in a mixed alkali borosilicate glass has been investigated by low energy bombardment induced ion transport employing Cs+ ions as the foreign ion. Electrodiffusion causes the replacement of Na+ and K+ down to about 200nm below the surface of the glass. Beyond this electrodiffusion front (in the direction of ion transport) K+ ions accumulate to a density above the bulk concentration while Na+ is further depleted towards the backside electrode. At the backside electrode only Na is electrodeposited since the electrical potential does not allow for K electrodeposition. A full simulation of the electrodiffusion profiles reveals the complete concentration dependence of the diffusion coefficients of the Na+ and K+ ions.
Redox flow batteries with flow field designs have been demonstrated to boost their capacities to deliver high current density and power density in medium and large-scale energy storage applications. Nevertheless, the fundamental mechanisms involved with improved current density in flow batteries with serpentine flow field designs have been not fully understood. Here we report a three-dimensional model of a serpentine flow field over a porous carbon electrode to examine the distributions of pressure driven electrolyte flow penetrations into the porous carbon electrodes. We also estimate the maximum current densities associated with stoichiometric availability of electrolyte reactant flow penetrations through the porous carbon electrodes. The results predict reasonably well observed experimental data without using any adjustable parameters. This fundamental work on electrolyte flow distributions of limiting reactant availability will contribute to a better understanding of limits on electrochemical performance in flow batteries with serpentine flow field designs and should be helpful to optimizing flow batteries.
MoSe2 nanoplatelets were synthesised by liquid phase exfoliation. MoSe2 nanoplatelets and MoSe2 nanoplatelets/SWCNTs electrodes were manufactured using a spray-deposition method and their charge storage properties were investigated in a 1 M LiPF6/EC/DMC electrolyte in a three-electrode cell and a 3-0V electrochemical window. MoSe2 nanoplatelets electrodes showed charge storage activity without the use of an electrically conductive additive. However, their rate performance and cycling stability was poor, which was improved by adding SWCNTs. The MoSe2 nanoplatelets/SWCNTs electrodes showed a capacity of 798mAhg−1 at a 0.05C rate (cycle 8), much higher than the capacity of a bulk MoSe2/carbon black electrodes of 557.0mAhg−1 at 0.05C (cycle 1). An improved rate performance, respect the bulk counterpart, from 0.1C (569mAhg−1) to 5C (153mAhg−1) rates, and a capacity retention of 58 % over 100 cycles at a 0.5C rate were achieved. The improved performance of the MoSe2 nanoplatelets/SWCNTs electrodes was attributed to the nanosize of the MoSe2 nanoplatelets and the combination with SWCNTs that provided mechanical stability.
Résumé Le dysfonctionnement cognitif est fréquent et précoce chez les patients atteints de sclérose en plaques (SEP). L’importance des troubles rencontrés est variable selon le domaine cognitif considéré mais les perturbations prédominent sur la mémoire de travail, les capacités attentionnelles, les fonctions exécutives, le raisonnement abstrait, la perception visuospatiale et la vitesse de traitement de l’information. Le recours à des tests psychométriques standardisés, reproductibles et permettant d’obtenir des indicateurs sensibles à l’existence et à l’évolutivité de ces troubles a été proposé, mais ceux-ci apparaissent peu spécifiques et particulièrement sensibles à l’apprentissage ou effet test re-test. Les supports morphologiques rendant compte de la présence et de la gravité des perturbations cognitives rencontrées dans la SEP restent discutés. Plus que l’importance et la distribution topographique des lésions, il semble que le facteur déterminant à l’apparition des troubles cognitifs soit représenté par l’atteinte diffuse et précoce de la substance blanche qui pourrait avoir un impact fonctionnel majeur sur la réalisation de tâches cognitives complexes sollicitant les grandes voies d’association intra et inter hémisphériques. Une meilleure approche des perturbations cognitives au stade précoce de la maladie pourrait permettre, d’une part d’intégrer celles-ci dans l’évaluation du degré de handicap, d’autre part d’envisager des procédures de prise en charge spécifiques.
In this paper, we report the synthesis of cross-linked copolymers of glycidyl methacrylate (GMA) and poly (ethylene glycol) methyl methacrylate (PEGMA) for use as solid polymer electrolytes (SPE). The cross-linking is performed with volatile ethylene diamine, thus preventing the accumulation of undesirable precursors in the final membrane. The structure of the cross-linked polymer electrolyte was investigated by 13C solid NMR and its physical properties were examined by DSC, TGA and stress-strain tests. The ionic conductivities were determined by AC Impedance, which showed that the SPEs have good conductivities (10−5 Scm−1) at 80 °C. The highest capacity measured with these polymers was 151 mAh g−1 at C/6 and 80 °C for a LFP/SPE/Lithium battery. The retention capacity is high, at 97% after 80 cycles at different rates of cycling. The Young's modulus of the membranes is as high as 1 GPa. The SEM images showed no evidence of lithium dendrites and no degradation after cycling. Therefore, the polymer is a good candidate for battery operation over a long time. Especially important is the ability of this polymer to prevent growth of dendrites on the Li-metal electrode.
The momentum in developing next-generation high energy batteries calls for an electrolyte that is compatible with both lithium (Li) metal anodes and high-voltage cathodes, and is also capable of providing high power in a wide temperature range. Here, we present a fluoromethane-based liquefied gas electrolyte with acetonitrile cosolvent and a higher, yet practical, salt concentration. The unique solvation structure observed in molecular dynamics simulations and confirmed experimentally shows not only an improved ionic conductivity of 9.0 mS cm−1 at +20 °C but a high Li transference number (tLi+ = 0.72). Excellent conductivity (>4 mS cm−1) was observed from −78 to +75 °C, demonstrating operation above fluoromethane's critical point for the first time. The liquefied gas electrolyte also enables excellent Li metal stability with a high average coulombic efficiency of 99.4% over 200 cycles at the aggressive condition of 3 mA cm−2 and 3 mA h cm−2. Also, dense Li deposition with an ideal Li–substrate contact is seen in the liquefied gas electrolyte, even at −60 °C. Attributed to superior electrolyte properties and the stable interfaces on both cathode and anode, the performances of both Li metal anode and Li/NMC full cell (up to 4.5 V) are well maintained in a wide-temperature range from −60 to +55 °C. This study provides a pathway for wide-temperature electrolyte design to enable high energy density Li–metal battery operation between −60 to +55 °C.
Mesoporous Sn–Cu composite consisting of Cu6Sn5 (active), Cu3Sn (inactive), and Sn is prepared by using silica SBA-15 as the hard template. As-prepared composite has a large BET surface area of 197.8m2 g−1 and a large pore volume of 0.517cm3 g−1. As the anode material for lithium ion batteries, no obvious capacity decay can be observed from 2nd to 20th cycles when the current density is 500mAg−1. It delivers much better cycling performance than bulk Sn–Cu composite without porous structure. The mesoporous structure can provide sufficient contact of the active material with the electrolyte, and can buffer volume changes of Sn in the electrochemical process. Charge transfer process is also found to be favored by using EIS measurements.
In this study, process for the formation of activated and mesoporous carbon nanofibers (CNF) and their electrochemical activities were investigated. The fibers were obtained using lignin/poly (vinyl alcohol) polymer blends as carbon precursor. Potassium hydroxide was used as pore-formation and activation agent and was applied in-situ before fiber production and after carbonization. The morphology and structure of fibrous mats were characterized by SEM, FTIR and Raman spectroscopy, while the effect of the activation methods on the surface area and porosity was investigated using BET analysis. All types of carbon nanofibers were further used as free-standing anodes in half cell lithium and sodium ion batteries and their charge/discharge behavior was tested at different current densities. The results showed that high cycling stability can be achieved when CNFs with mesoporous structures are used as anodes for both lithium and sodium ion cells.
A one-step synthesis method is developed to prepare the Li[Ni0.5Co0.2Mn0.3]O2 (NCM 523) cathode with uniform tungsten-coating layer for lithium-ion battery. Such modified material shows similar properties with the bare NCM 523 in terms of the primary particles, secondary structure, and specific capacity. With W coating layer, the NCM 523 gives remarkable improvement in the long-term capacity retention in the half-cell testing, which is sharply inconsistent with the result from the full-battery tests, indicating a contradiction between the half-cell and full-battery tests in some case. After further investigations, such conflict between the half-cell and full-cell tests in evaluating the W-coating strategy is attributed to the dissolution of Li2WO4 layer in the electrolyte, which probably destroys the solid electrolyte interface (SEI) on the graphite anode and irreversibly consumes the active lithium ions for renovating SEI in full-cell testing. These results will benefit researchers in the area of lithium-ion batteries to fully understand the differences between the half-cell and full-cell testing, and develop the effective strategies for cathode modifications.
Stiffness is one of the basic performance parameters for railway track. The efficient and accurate stiffness measurement has been considered as the foundation for further development of railway engineering, and therefore has great theoretical and practical significance. Based on a summary of the connotation and measurement of track stiffness, the state of the art of measurement methods for track stiffness was analyzed systematically. The standstill measurement of track stiffness can be performed with the traditional jack-loading method, impact hammer method, FWD (falling weight deflectometer) method, and track loading vehicle method. Although these methods can be adopted in stiffness measurement for a section of railway track, they are not desirable owning to small range and low efficiency. In the recent 20 years, researchers have proposed many methods like unbalanced-loading laser displacement method, deflection basin deformation rate method, and eccentricity excitation method to continuously measure track stiffness; however, these methods have drawbacks like poor accuracy, low speed, and insufficient data analysis. In this work, the merits and demerits of these methods were summarized, and optimization suggestions were presented. Based on the wave transmission mechanism and principle of vibration energy harvesting, an overall conception on continuous measurement of stiffness and long-term stiffness monitoring for special sections was proposed.
This paper presents a methodology to systematically formulate a hybrid renewable energy system (HRES), which consists of solar, wind and diesel generator as a backup resource as well as battery storage, from the preliminary design stage to the optimal operation. Detailed modeling of each system component is introduced as the basis for the simulation study. System sizing considering energy flows is conducted to obtain the optimal combination of photovoltaic (PV) panels and wind turbines. Energy management strategies from both the demand-side and generation-side are developed to realize the objectives of meeting the electricity demand while minimizing the overall operating and environmental costs. Day-ahead and real-time weather forecasting, demand response and model updating are also integrated into the proposed methodology using a receding horizon optimization strategy. The method is demonstrated through an application to a single-family residential home.
Me/Al-layered double hydroxides (Me=Ni and Co) prepared by the chemical co-precipitation method have been shown to be outstanding novel materials for electrochemical capacitors. The crystalline structure and the electrochemical properties of the electrodes have been studied by considering the effect of the mole ratio of nickel/cobalt. X-ray diffraction analysis shows that the materials belong to hexagonal system with layered structure. Cyclic voltammetric measurements indicate that Me/Al-layered double hydroxides with the Ni/Co mole ratio of 4:6 exhibit excellent capacitive properties within the potential range of 0.0–0.6V versus Hg/HgO in 6mol/L KOH electrolyte. Charge/discharge behaviors have been observed with the highest specific capacitance values of 960F/g at the current density of 400mA/g. Impedance studies show that the enhanced electrical properties and high frequency response are attributed to the presence of Co oxides.
Despite possessing a high theoretical capacity, MnS has a rather complex lithium kinetic diffusion and poor mechanical stability that hinders its application in energy storage devices like lithium-ion batteries. This study is focused on overcoming the drawbacks of MnS anode material by assembling a carbon-constraint MnS nanocomposite in a core-shell configuration. This structure is obtained by a simple route involving DC plasma evaporation of Mn@C nanoparticles and posterior thermal sulfurization process. As anode material in a Li-ion battery, MnS@C-300 attains high specific capacity of 890 mAh g−1 after 500 cycles at 500 mA g−1. It also shows remarkable high rate capability with capacity values of 705, 684, 643, 578, and 495 mAh g−1 at current densities of 100, 200, 500, 1000, and 2000 mA g−1, respectively. This exceptional electrochemical response is endorsed to the synergetic effect of the smart design of a core-shell architecture. The carbonaceous shell enhances the lithium-ion diffusion towards the active MnS core and preserves structural stability during the long cycling process.