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One-dimensional porous Co3O4 nanowires with different length have been successfully synthesized by thermal decomposition of Co-NA polymer precursors at various hydrothermal reaction times. The positive effects of longer nanowires and larger surface area on electrochemical performance of Co3O4 samples were investigated systematically. All the as-prepared Co3O4 samples display excellent discharge capacities and cycle stability on account of large surface area and porous structure, indicating great potential application of porous Co3O4 nanowires for alkaline rechargeable batteries. The Co3O4-24 h sample with the longest length shows the most outstanding electrochemical performance, and displays the maximum discharge capacity of 450.1 mAh g−1 with the capacity retention of 90.4% after 100 cycles at a current density of 100 mA g−1. Electrochemical reactions between Co and Co(OH)2 occurring on the Co3O4 electrodes are investigated by XRD, cyclic voltammetry (CV) and charge–discharge measurements.
We develop three types of organic–inorganic composite membranes based on a semi-interpenetrating polymer network (SIPN) to explore the effects of membrane structure on the possible operating current densities of a non-aqueous redox flow battery (RFB) system. Poly(vinylidene fluoride) (PVdF) is selected as a supporting polymer matrix for improving the chemical and thermal stability of the organic–inorganic composite membranes. We also introduce silica nanoparticles (5 wt% of PVdF) into the membranes to ensure the low crossover of active species. The fabrication of SIPN through the addition of glycidyl methacrylate, 4-vinylpyridine, or N-vinylcarbazole enables control of the membrane structure. Depending on monomer type, the membrane structure is determined to be either aliphatic or aromatic in terms of chemical properties and either dense or porous in terms of physical properties. These chemical and physical structures affect the electrochemical properties that correspond to charge/discharge performance and to the range of possible operating current densities. An important requirement is to examine charge/discharge performance at the possible range of operating current densities by using various membrane structures. This requirement is discussed in relation to a proposed design strategy for non-aqueous RFB membranes.
Proton exchange membrane fuel cells (PEMFCs) are considered to be an important low-carbon energy conversion technology, which has shown impressive performance improvement in the past decades. However, the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode has been an impediment to the successful commercialization of the technology. Novel highly active electrocatalysts for the ORR are highly desired to meet the US DOE performance targets. In recent years, polyhedron-engineered Pt-alloy nanocrystals have demonstrated unprecedented electrocatalytic activity. Different from previous reviews on shape-manipulated Pt-based ORR catalysts, this review focuses on 3D polyhedron-engineered Pt-based nanocrystal electrocatalysts with an in-depth comparison of different active facet-tailored geometric configurations and their advanced electrocatalytic properties. The review carefully examines and criticizes the aggregated data in this area, and provides an important overview as well as a critical insight into the topic. Understanding the catalytic mechanism taking place with polyhedron-designed Pt-based nanocrystals helps to unlock the door to highly active ORR electrocatalysts for PEMFC applications.
Paramount attention has been paid on solid polymer electrolytes due to their potential in enhancement of energy density as well as improvement of safety. Herein, the composite electrolytes consisting of Li-salt-free polyethylene oxides and 200 nm-sized Li6.4La3Zr1.4Ta0.6O12 particles interfacially wetted by [BMIM]TF2N of 1.8 μL cm−2 have been prepared. Such wetted ionic liquid remains the solid state of membrane electrolytes and decreases the interface impedance between the electrodes and the electrolytes. There is no release of the liquid phase from the PEO matrix when the pressure of 5.0 × 104 Pa being applied for 24 h. The interfacially wetted membrane electrolytes show the conductivity of 2.2 × 10−4 S cm−1 at 20 °C, which is one order of magnitude greater than that of the membranes without the wetted ionic liquids. The conduction mechanism is related to a large number of lithium ions releasing from Li6.4La3Zr1.4Ta0.6O12 particles and the improved conductive paths along the ion-liquid-wetted interfaces between the polymer matrix and ceramic grains. When the membranes being used in the solid-state LiFePO4/Li and LiFe0.15Mn0.85PO4/Li cells at 25 °C, the excellent rate capability and superior cycle stability has been shown. The results provide a new prospect for solid polymer electrolytes used for room-temperature solid-state lithium batteries.
This paper presents a experimentally-validated fractal time thermal model to describe the discharge and cooling down processes of air-cooled cylindrical Lithium-ion cells. Three cases were studied, a spatially isolated single cell under natural convection and two spatial configurations of modules with forced air cooling: staggered and aligned arrays with 30 and 25 cells respectively. Surface temperature measurements for discharge processes were obtained in a single cell at 1 C, 2 C and 3 C discharge rates, and in the two arrays at 1 C discharge rate. In the modules, surface temperature measurements were obtained for selected cells at specific inlet cooling air speeds. The fractal time energy equation captures the anomalous temperature relaxation and describes the cell surface temperature using a stretched exponential model. Stretched exponential temperature models of cell surface temperature show a better agreement with experimental measurements than pure exponential temperature models. Cells closer to the horizontal side walls have a better heat dissipation than the cells along the centerline of the module. The high prediction capabilities of the fractal time energy equation are useful in new design approaches of thermal control strategies of modules and packs, and to develop more efficient signal-correction algorithms in multipoint temperature measurement technologies in Li-ion batteries.
A novel composite material of SnO2/ordered mesoporous carbon (SnO2/OMC) was prepared through a hydrolysis process. The morphology, structure and composition of the SnO2/OMC was characterized by using powder X-ray diffraction (low-angle and wide-angle diffraction patterns), transmission electron microscopy (TEM), thermogravimetric analysis (TG-DTA) and nitrogen-adsorption measurement. Cyclic voltammetry (CV) and galvanostatic discharge–charge measurements were used to test the electrochemical performance of the SnO2/OMC. It has found that the SnO2/OMC composite could deliver a reversible capacity as high as 395.6mAhg−1 up to 50cycles of discharge/charge. The results demonstrated also a good rate capability. When the charge current density was increased gradually from 200 to 1000mAg−1 and then returned immediately to 200mAg−1, 75% of the initial capacity at 200mAg−1 has been recovered. Therefore, the SnO2/OMC is revealed as a promising candidate of anode material for high energy and high power lithium ion batteries (LIBs).
The cobalt-substituted tin dioxide nanocrystals were synthesized by the one-pot hydrothermal method. According to the powder X-ray diffraction and elemental analyses, the cobalt ions were successfully substituted into the rutile lattice of the SnO2 phase, which consequently resulted in an increase in the volume of the unit cell. Electron microscopy revealed that with an increase in the content of the substituted cobalt ions, the particle size of the SnO2 nanocrystals becomes smaller. In addition, the X-ray absorption spectroscopy clearly demonstrated that the substituent cobalt ions were stabilized in a divalent oxidation state in a distorted octahedral symmetry, while the tin ions were in a tetravalent oxidation state. The electrochemical measurements revealed that the substitution of Sn with Co significantly enhanced the negative electrode performance of tin dioxide nanocrystals at optimal Co content. The present study clearly demonstrated that a partial substitution of cobalt in the SnO2 phase can provide an effective way of optimizing the electrochemical properties of the tin dioxide nanocrystals.
An intelligent battery to monitor battery states for an automotive use was newly developed. A main parameter to monitor battery states are based on the measurement of voltage variations that are to fluctuate immediately after an engine ignition. The developed monitoring unit is embedded into the lead-acid battery “CYBOX®” which does not have a current monitoring unit. The monitoring unit that has an alarm system which is compact and highly reliable essentially diagnoses the state of charge and the state of health of battery states in order to inform automotive user of the adequate timing of replace, recharge, and the hazardous state of overcharge of batteries. The battery-monitoring unit has an optical data transfer system to extract internal data from external device. The battery-monitoring unit also has a data acquisition instrument which receives more detailed monitored historical data from the optical data transfer system of the monitoring unit.
Co-doped lithium manganese oxide (LiCoxMn2-xO4) cathodes were prepared as thin films via a sol-gel process to investigate the effects of the octahedral Co substitution on electrochemical properties. X-ray diffraction and scanning electron microscopy results showed that the polycrystalline films (x≤0.3) were composed of phase-pure grains with the sizes distributed mainly in 100–200nm range. The cubic lattice parameters of the spinel LiCoxMn2-xO4 samples decreased gradually with increasing Co composition. X-ray photoelectron spectroscopy data indicated that cobalt ions in LiCoxMn2-xO4 exist as Co3+ mostly. The electrochemical investigations of LiCoxMn2-xO4 cathodes include cyclic voltammetry, cycling performance, charge-discharge profile, and rate capability in the 3.5–4.3V potential range. The x=0.05 cathode exhibited initial discharge capacity close to that of LiMn2O4 cathode and less capacity fading than LiMn2O4 after extended charge-discharge cycles (>200). The x=0.1 cathode exhibited a reduction in initial discharge capacity by ∼10% but the capacity was retained up to ∼300 cycles. The improved capacity retention of LiCoxMn2-xO4 cathodes is attributable to the improved structural stability by octahedral Co3+ substitution for suppressing Mn3+-related Jahn-Teller distortion and cathode dissolution into electrolyte.
In this study, we present a physicochemical model considering both lithium plating and lithium stripping side reactions in lithium-ion batteries. The model shows the amount of reversibly plated lithium dependent on the charging current on the surface of the graphite anode. In the subsequent discharge, a characteristic voltage plateau due to lithium stripping is simulated. The shape of the voltage plateau corresponds to the amount of previously plated lithium. The model correlates with experimental data of a commercial 18650-type NMC/C cell. The simulated amount of plated lithium is in the same range as in a previous neutron diffraction study with the same cell type. To induce lithium plating, the cells are charged with various C-rates at an ambient temperature of 0 °C. The measured voltage plateau caused by lithium stripping in the discharge is correctly described by simulation.
Modified activated carbon (Norit S-50) electrodes with electrochemical double layer (EDL) capacitance and redox capacitance contributions to the electric charge storage were tested in 1 M H2SO4 to quantify the benefit and the limitation of the surface redox reactions on the electrochemical performances of the resulting pseudo-capacitive materials. The electrochemical performances of an electrochemically anodized carbon electrode and a catechol-modified carbon electrode, which make use both EDL capacitance of the porous structure of the carbon and redox capacitance, were compared to the performances obtained for the pristine carbon. Nitrogen gas adsorption measurements have been used for studying the impact of the grafting on the BET surface area, pore size distribution, pore volume and average pore diameter. The electrochemical behavior of carbon materials was studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The EIS data were discussed by using a complex capacitance model that allows defining the characteristic time constant, the global capacitance and the frequency at which the maximum charge stored is reached. The EIS measurements were achieved at different dc potential values where a redox activity occurs and the evolution of the capacitance and the capacitive relaxation time with the electrode potential are presented. Realistic galvanostatic charge/discharge measurements performed at different current rates corroborate the results obtained by impedance.
Solid state secondary cells were constructed with Prussian blue (PB), i.e. iron (III) hexacyanoferrate (II) as the active material for cathodes and zinc (II) hexacyanoferrate (III) (Znhcf) and copper (II) hexacyanoferrate (III) (Cuhcf) as the active materials for anodes. The metal hexacyanoferrates were mixed with graphite powder, potassium chloride and dilute hydrochloric acid to form a thick paste. A Nafion membrane was used as separator transporting protons only. Charge–discharge studies were carried out using galvanostatic method and double step chronopotentiometric method. The cell voltage at half-discharge for Znhcf/PB cell varied from 0.6 to 0.8 V depending on the discharge rate. For the Cuhcf/PB cell, the cell voltage at half-discharge was 0.87 V for a precycled cell and it dropped to 0.75 V after 100 cycles. The practical capacity of the Znhcf/PB cell (12 A h/kg) was higher than that of the Cuhcf/PB cell (5 A h/kg), however, the recycling efficiency of the latter was far better than that of the former. Open-circuit voltage decay and recovery transients were recorded for both cells and analysed.
Mixed metal oxide (MMO) electrodes have been applied to different technologies including chlorine production, organic compounds oxidation, water electrolysis, electroplating, etc. due to their catalytic, optical and electronic properties. Most of the existing MMO electrodes contain either toxic metals or precious metals of the platinum group. The aim of this study was to develop environmentally friendly and cost-effective MMO electrodes for water and organic compounds oxidation. Ti/Ta2O5-SnO2 electrodes of different nominal composition were prepared, and electrochemically and physically characterized. For water oxidation, Ti/SnO2 electrode with 5 at.% of Ta produced the highest electroactivity. Ti/SnO2 electrode with 7.5 at.% of Ta showed the best performance for the oxidation of methylene blue (MB). The electrocatalytic activity of the Ti/Ta2O5-SnO2 electrodes increased with the number of active layers. The maximum current of water oxidation reached 3.5mA at 2.5V when the electrode was covered with ten layers of Ta2O5. In case of the oxidation of 0.1mM MB, eight and ten active layers of Ta2O5 significantly increased the electrode activity. The prepared electrodes have been found applicable for both water electrolysis and organic compounds oxidation.
Bikini Island was contaminated on March 1, 1954 by the Bravo detonation (U.S. nuclear test series, Castle) at Bikini Atoll. About 90% of the estimated dose from nuclear fallout to potential island residents is from cesium-137 (137Cs) transferred from soil to plants that are consumed by residents. Thus, radioecology research efforts have been focused on removing 137Cs from soil and/or reducing its uptake into vegetation. Most effective was addition of potassium (K) to soil that reduces 137Cs concentration in fruits to 3–5% of pretreatment concentrations. Initial observations indicated this low concentration continued for some time after K was last applied. Long-term studies were designed to evaluate this persistence in more detail because it is very important to provide assurance to returning populations that 137Cs concentrations in food (and, therefore, radiation dose) will remain low for extended periods, even if K is not applied annually or biennially. Potassium applied at 300, 660, 1260, and 2070kgha−1 lead to a 137Cs concentration in drinking-coconut meat that is 34, 22, 10, and about 4% of original concentration, respectively. Concentration of 137Cs remains low 8–10y after K is last applied. An explanation for this unexpected result is discussed.
The chemical and electrochemical stability of Cu current collectors in electrolyte for lithium-ion batteries is investigated. During long-term storage, the surface section of Cu foil is oxidized to copper compounds along with the reduction reaction of electrolyte. A continuous surface film can be formed on the Cu current collector after the foil is immersed in electrolyte for lithium ion batteries at room temperature for 30 days. This surface film is composed of inorganic compounds located in the inner layer and organic/inorganic mixed components stayed outside. It comes from the spontaneous reaction at the interface between Cu foil and electrolyte for the existence of trace water in electrolyte. Different from SEI film spontaneous formation during storage, surface film generated on Cu foil during electrochemical process shows different characteristic and mechanism. By using metal lithium as counter electrode, SEI film on Cu foil in Cu foil/metal Li battery is formed from surface chemical species floating from lithium counter electrode and electrochemical oxidation/reduction process. In contrast, thinner SEI film can be generated merely from electrochemical electrolyte decomposition and precipitation. All the evidences reveal that the structure of SEI film from different conditions is similar, which shows inorganic fluorides located in the inner layer and organic/inorganic mixed lied in the outer layer.
The β-Co(OH)2 sheets with uniform hexagonal shape were prepared using NaBH4 as the structure directing agent at room temperature. After thermal annealing in air at 450°C for 2h, the as-prepared β-Co(OH)2 sheets were converted into porous Co3O4 with the hexagonal sheet-like morphology (H-Co3O4). The textural properties of the as-prepared samples were characterized by field-emission scanning electron microscopy, transmission electron microscopy and powder X-ray diffraction. The results of lithium storage capability indicate that the H-Co3O4 electrode exhibits excellent cycleability and rate capacity. At a charge/discharge current density of 50mAg−1, a reversible capacity of 914mAhg−1 can be maintained after 40 cycles. When the current density is increased to 1600mAhg−1, a reversible capacity of 800mAhg−1 can be still obtained. The superior electrochemical performance is attributed to the porous 2D structures with a finite lateral size and enhanced open-edges, which facilitate Li-ion and electron diffusion through active materials.
We report a simple and effective carbon-free nanocoating strategy for large-scale synthesis of Mo2N nanolayer coated MoO2 hollow nanostructures. This strategy only involves commercial MoO3 powders reacted with reduced gas. The carbon-free nanocoating of Mo2N is highly effective in improving the electrochemical properties of MoO2, promising advanced batteries with high specific capacity up to 815 mA h g−1, long cycle-life (e.g., >100 cycles) and high rate capability compared with the carbon nanocoating commonly used in electrode materials. The present nitride-nanocoating strategy is facile but effective, and therefore it is very promising for large-scale industrial production. It may be extended to prepare other metal oxides with nitride coating nanolayers to enhance their performances as electrode materials.
People wish to enjoy their everyday lives in various ways, among which entertainment plays a major role. In order to improve lifestyle with more ready access to entertainment content, we propose BlueTorrent, a P2P file sharing application based on ubiquitous Bluetooth-enabled devices such as PDAs, cellphones and smart phones. Using BlueTorrent, people can share audio/video contents as they move about shopping malls, airports, subway stations etc. BlueTorrent poses new challenges caused by limited bandwidth, short communications range, mobile users and variable population density. A key ingredient is efficient peer discovery. This paper approaches the problem by analyzing the Bluetooth periodic inquiry mode and by finding the optimum inquiry/connection time settings. At the application layer, the BlueTorrent index/block dissemination protocol is then designed and analyzed. The entire system is integrated and implemented both in simulation and in an experimental testbed. Simulation and measurement results are used to evaluate and validate the performance of BlueTorrent in content sharing scenarios.
The present work provides an alternative straight-forward process protocol to achieve a binder-free electrode material with optimal performance for the large scale fabrication and application in electrochemical energy storage. The conventional method for the preparation of electrodes, also called slurry-coating technique, suffers some difficulty in boosting the high performance and large-scale industrial fabrication of electrode materials. It becomes equally urgent to develop advanced electrode materials and to design superior electrode architectures. Here, we prepared a flexible binder-free electrode material by anchoring ethylene glycol (EG) intercalated cobalt and nickel layered double hydroxide nanosheets on Ni foam (E–Co–Ni LDH/Ni foam) via a facile effective vacuum freeze-drying technique, following a modified coprecipitation. By this way, the complex steps in the slurry-coating process were avoided and excessively aggregating of the E–Co–Ni LDH nanosheets was refrained from, which supply high accessible surface area and large number of micro/mesopores for electrochemical reaction. When directly used as a supercapacitor electrode, the E–Co–Ni LDH/Ni foam displayed a high specific capacitance of 774Fg −1 at the current density of 0.2Ag−1 with a unique cyclability at a high load mass of 3.27mgcm−2.
The effect of separator pore size on lithium dendrite growth is assessed through the use of the phase field method (PFM). Dendrites are found to undergo concurrent electrodeposition and electrodissolution that define their local growth or shrinkage. Moreover, dendrites are observed to detach due to localized electrodissolution and generate metallic debris that is detrimental to battery performance. A critical current density exists below which dendrites are fully suppressed. An analytical model based on the performed PFM simulations allows to formulate the critical current density as a function of separator morphology and pore radius. Four distinct regimes of dendrite growth are identified: (i) the suppression regime, where dendrite growth is thermodynamically unfavorable; (ii) the permeable regime, where dendrite growth is prohibited beyond the first layer of the separator; (iii) the penetration regime, in which dendrites are stable within the channels of the separator; and (iv) the short circuit regime, where dendrites penetrate the entire width of the separator causing a short circuit. The identification of these regimes serve as a guideline to design improved separators.