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The study investigates the effects of arrangements to the electrochemical performances of carbon fluorides (CF x )/manganese dioxide (MnO2) hybrid cathodes. When CF x and MnO2 are in parallel arrangement (denoted as CF x ∥MnO2), the hybrid cathode exhibits the best electrochemical performances than other types of arrangements, such as the mixed or stacked types. Based on the various electrochemical measurements, such as impedance spectra and galvanostatic intermittent titration technique, the charge transfer takes place at the interface of MnO2 and CF x particles because of the special arrangement in the CF x ∥MnO2 hybrid cathode, in which the continuous MnO2 phase guarantees and facilitates the lithium ions transfer from electrolyte to current collector due to the lower charge transfer resistance. Therefore, CF x ∥MnO2 exhibits the best rate capability, and the maximum delivered power density is up to 6599 W kg−1 at 5C, associated with the energy density of 1814 Wh kg−1.
LiFePO4 is a potential cathode material for 4V lithium-ion batteries. Carbon-coated lithium iron phosphates were prepared using a high surface area carbon to react precursors through a solid-state process, during which LiFePO4 particles were embedded in amorphous carbon. The carbonaceous materials were synthesized by the pyrolysis of peanut shells under argon, where they were carbonized in a two-step process that occurred between 573 and 873K. The shells were also treated with a proprietary porogenic agent with the goal of altering the pore structure and surface area of the pyrolysis products. The electrochemical properties of the as-prepared LiFePO4/C composite cathode materials were systematically characterized by X-ray diffraction, scanning electron microscope, element mapping, energy dispersive spectroscopy, Raman spectroscopy, and total organic carbon (TOC) analysis. In LiFePO4/C composites, the carbon not only increases rate capability, but also stabilizes capacity. In fact, the capacity of the composites increased with the specific surface area of carbon. The best result was observed with a composite made of 8.0wt.% with a specific surface area of 2099m2 g−1. When high surface area carbon was used as a carbon source to produce LiFePO4, overall conductivity increased from 10−8 to 10−4 Scm−1, because the inhibition of particle growth during the final sintering process led to greater specific capacity, improved cycling properties and better rate capability compared to a pure olivine LiFePO4 material.
Early identification of possible risk factors that could impair the motor development is crucial, since poor motor performance may have long-term negative consequences for a child's overall development. The aim of the current study was the examination of disorders in motor coordination in Greek pre-school aged children and the detection of differences in motor performance with regards to age, gender, participation in sports and order of birth in the family. Performance profiles on the movement ABC were used to classify 412 Greek children aged 4–6years old. It appears from the results that the occurrence rate of probable developmental coordination disorders (DCD) was 5.4%. Significant differences were observed in all independent variables except the order of birth in the family. The findings reinforce the need for the evaluation of motor performance in preschool-aged children, in order specific individual motor profiles to be established for optimizing and adapting early intervention programs.
A hybrid biofuel cell has been constructed based on the Zn anode and O2 biocathode, exploiting fungal Cerrena maxima and Choriolus hirsutus laccases cross-linked onto graphite and microstructured graphitized carbon cloth (GCC) electrodes. Immobilized at the graphite electrodes, laccases exhibited a high similarity in the reaction of direct (in the absence of any mediators) bioelectrocatalytic reduction of O2 starting from 0.7V vs. Ag/AgCl, pH 5, which was consistent with a 94% structural homology of the laccases. The efficiency of the bioelectrocatalytic reaction was enhanced by immobilizing laccases on the high-surface area GCC, due to the increased surface concentration of the laccase molecules properly orientated for the direct electron transfer reaction within the micro-structured electrode. The hybrid biofuel cell, based on the battery-type Zn anode and oxygen laccase/GCC biocathode yielded the open-circuit voltage V oc of 1.76V and the short-circuit current density j sc of 4mAcm−2 in quiescent aerated solutions. A maximum power density of the cell was 0.44mWcm−2 at the cell voltage of 0.5V, pH 5. The hybrid biofuel cell exploiting cross-linked stabilized laccases at GCC was able to power a 1.5V domestic device for 38 days.
In attempt to utilize spinel compound, a blend type of positive electrode, Li1.1Mn1.9O4 and LiNi0.8Co0.15Al0.05O2 (1:1 in weight), was representatively investigated. Though spinel Li1.1Mn1.9O4 is modified by Li replacement at Mn sites, its capacity fading was inevitable by HF attack into the electrolyte at 25°C and especially at 60°C. The specific discharge capacity of the mixed positive electrode, Li1.1Mn1.9O4 and LiNi0.8Co0.15Al0.05O2 (1:1 in weight), had a sum average value of Li1.1Mn1.9O4 and LiNi0.8Co0.15Al0.05O2 electrodes. Interestingly, the mixed positive electrode had greatly improved capacity retention even at 60°C. The capacity fading was only of about 8mAhg−1 by applying 1C rate (150mAg−1) during 100 cycles. In the full cell test utilizing graphite as the negative electrode, the retained capacity was about 96% of its initial capacity by applying 1C current at 25°C. It is suggested that the mixed electrode is considered to be a quite promising positive electrode material to be applied for lithium-ion batteries.
A miniaturized, porometer-compatible cuvette for measurements of CO2 efflux from woody plant parts at controlled temperature conditions is described. A copper cuvette equipped with a PID-controlled Peltier element regulates cortex temperature in three modes: (1) synchronized with ambient air temperature; (2) at a constant difference in the range of ±10°C from air temperature; and (3) constant at a temperature in a range of ±25°C difference from ambient air. This method allows investigation of (a) respiratory capacity of woody plant parts dependent on short-term temperature variations, (b) CO2 release from woody plant parts following exposure to the sun, and (c) acclimation of woody plant parts to long-term changes of temperature. By use of the copper cuvette, temperature gradients in the cortex are drastically reduced. Therefore, studies on the effect of metabolically and physico-chemically based processes on diurnal variations of CO2 efflux from woody plant parts can be carried out. Field experiments were carried out on trees of Betula pendula, B. ermanii, and B. litwinowii. At synchronized temperatures of ambient air and woody plant tissue, daytime reductions of CO2 efflux relative to night-time rates at a given temperature from branches of B. pendula and B. ermanii were observed. In July, CO2 efflux from branches of B. litwinowii under controlled temperature conditions from 3 to 27°C showed a characteristic exponential increase from 0.6 to 7.2 µmol CO2 m−2 s−1. During dormancy, long-term warming of branches of B. ermanii failed to increase metabolic activity.
In this work, we designed a facile in-situ template-sacrificial route to prepare LiNi1/3Co1/3Mn1/3O2 hollow microspheres with an average diameter of 2.0μm for the first time through using porous spinel Mn1.5Co1.5O4 hollow microspheres as the template, the formation of which could originate from a synergic effect of the contraction and adhesion action generated during the oxidative decomposition of the Mn0.5Co0.5CO3 precursors. The walls of the as-prepared hollow microspheres are ~300nm in thickness, and composed of numerous primary particles with size of hundreds of nanometers. The as-synthesized nanocrystal-assembled hollow structure showed singnificantly enhanced electrochemical performance with high capacity, excellent cycling stability and good rate capability, compared with the bulk counterparts, when used as a cathode material for Li ion batteries (LIBs), which can be attributed to the unique nano/micro hierarchical structure. Specifically, the resulting LiNi1/3Co1/3Mn1/3O2 hollow microspheres achieve a high discharge capacity of 157.3mAhg−1 at 0.2C after 100 cycles and 120.5mAhg−1 at 0.5C after 200 cycles with an excellent cycle life. Interestingly, it exhibits a high rate capacity of 114.2mAhg−1 even at a current of 1Ag−1 (5C). On the basis of this work, the pesent preparation strategy could provide an effective and general approach to improve the cyclability and rate capability of high-capacity cathode materials with hollow interiors for the application of LIBs.
A novel preparation technique was developed for synthesizing Li2FeSiO4/C nanoparticles through combustion of reaction mixtures containing silicon source, Li and Fe sources that operate as oxidizers and sucrose that act as a fuel. A systematic investigation of the synthesis parameters, such as the effect of the fuel content, on purity, morphology and electrochemical properties of the samples was performed. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area (BET) and electrochemical measurements, respectively. Among the synthesized cathode materials, Li2FeSiO4 obtained with 1.5mol of sucrose, showed the best electrochemical performance in terms of discharge capacity, cycling stability and rate capability. Discharge capacity of 130mAh/g at C/20, 88mAh/g at C/2 and 44mAh/g at 2C were obtained with no capacity fading after 50 cycles.
We have presented a detailed investigation of the effects of Mg substitution on the structure, electrochemical performance and Na-ion diffusion in high voltage P2-type Na2/3Ni1/3−xMgxMn2/3O2 (0 < x < 0.2) cathode materials for Na-ion batteries. Structural analysis using neutron diffraction showed that Mg2+ substitutes at Ni2+ sites from ordered [(Ni2+/Mn4+)O6] honeycomb units along the ab-plane, leading to an AB-type structure that can be indexed using the P63 space group. Within the sodium layers, high Mg-substitution levels (i.e. x = 0.2) caused a disruption in the typical Na zig-zag ordering observed in the undoped material, leading to a more disordered Na distribution in the layers. Load curves of the x = 0.1 and 0.2 materials show smooth electrochemistry, indicative of a solid-solution process. Furthermore, DFT calculations showed an increase in Na-ion diffusivity for the Mg-substituted samples. Enhanced cycling stability was also observed in these materials; structural analysis using high-resolution in operando synchrotron X-ray diffraction show that such an improved electrochemical performance is caused by the suppression of the O2 phase and switch to the formation of an OP4 phase. Ab initio studies support our experimental evidence showing that the OP4 phase (cf. O2) is the most thermodynamically stable phase at high voltages for Mg-substituted compounds. Finally, we have provided evidence using diffraction for the x = 1/2 and x = 1/3 intermediate Na+-vacancy ordered phases in P2-Na2/3Ni1/3Mn2/3O2.
A quasi-solid-state electrolyte consisting of tetraethylene glycol dimethyl ether (tetraglyme, G4)/lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) mixtures together with fumed silica nanoparticles was prepared for use as the electrolyte of an all-solid-state lithium rechargeable battery. Via the liquid route, we have succeeded in fabricating a quasi-solid-state electrolyte regardless of the high concentration of G4/Li-TFSA such as 75 vol%. It was found that the conductivities, the self-diffusion coefficients and the structure of the G4/Li-TFSA complex in the quasi-solid-state composite are essentially similar to those of the bulks regardless of the solid-like appearance. Compared to the quasi-solid-state electrolytes containing the conventional room temperature ionic liquids (RTILs), the ones containing the equimolar G4/LiTFSA complex exhibited a higher stability to the lithium electrodes. The all-solid-state lithium rechargeable battery was assembled using LiCoO2 and lithium metal as the cathode active material and anode, respectively. The all-solid-state cells showed noticeable charge–discharge and cycle performances. In the cut-off voltage range of 4.3–3.4 V, it achieved high initial discharge capacities of 130, 110 and 90 mAh g−1 at 0.05, 0.1 and 0.2 C, respectively. Even after one hundred charge–discharge cycles, the discharge capacities remained high at 105, 100 and 95 mAh g−1, respectively.
Although the structure of executive function (EF) during adulthood is characterized by both unity and diversity, recent evidence suggests that preschool EF may be best described by a single factor. The latent structure of EF was examined in 228 3-year-olds using confirmatory factor analysis. Children completed a battery of executive tasks that differed in format and response requirements and in putative working memory and inhibitory control demands. Tasks appeared to be age appropriate, with adequate sensitivity across the range of performance and without floor or ceiling effects. Tests of the relative fit of several alternative models supported a single latent EF construct. Measurement invariance testing revealed less proficient EF in children at higher sociodemographic risk relative to those at lower risk and no differences between boys and girls. At 3years of age, when EF skills are emerging, EF appears to be a unitary, more domain-general process.
Learning and memory impairments are present in schizophrenia (SZ) throughout the illness course and predict psychosocial function. Abnormalities in prefrontal and hippocampal function are thought to contribute to SZ deficits. The radial arm maze (RAM) is a test of spatial learning and memory in rodents that relies on intact prefrontal and hippocampal function. The goal of the present study was to investigate spatial learning in SZ using a virtual RAM. Thirty-three subjects with SZ and thirty-nine healthy controls (HC) performed ten trials of a virtual RAM task. Subjects attempted to learn to retrieve four rewards each located in separate arms. As expected, subjects with SZ used more time and traveled more distance to retrieve rewards, made more reference (RM) and working memory (WM) errors, and retrieved fewer rewards than HC. It is important to note that the SZ group did learn but did not reach the level of HC. Whereas RM errors decreased across trials in the SZ group, WM errors did not. There were no significant relationships between psychiatric symptom severity and maze performance. To our knowledge, use of a virtual 8-arm radial maze task in SZ to assess spatial learning is novel. Impaired virtual RAM performance in SZ is consistent with studies that examined RAM performance in animal models of SZ. Results provide further support for compromised prefrontal and hippocampal function underlying WM and RM deficits in SZ. The virtual RAM task could help bridge preclinical and clinical research for testing novel drug treatments of SZ.
A hybrid PV-battery-diesel configuration is very attractive for stand-alone systems in terms of cost and reliability. In many applications, the battery and the diesel generator are centralized and generate the AC grid while the PV generators and loads are distributed and are connected to the grid. However, in these cases, long communication cables are required in order to reduce the PV power when the battery is fully charged. This paper proposes an energy management strategy which makes it possible to avoid the use of communication cables, rendering the system simpler, cheaper and more reliable. The strategy dictates that should a power reduction be required, the battery inverter increases the grid frequency. This is detected by the PV inverters, which continuously reduce their power in order to prevent the battery from overcharge or over-current. The strategy also optimizes the efficiency and operating life of the diesel generator. Simulation and experimental validation are carried out for a system with 10 kW PV generation, a 5 kVA battery inverter, a 5 kVA diesel generator and a 5 kVA load.
A large proportion of the population of Nigeria reside in the rural communities. In this work, the financial costs of providing centralized (photovoltaic) PV generating system of various capacities—to satisfy different load requirements—in a remote village in Nigeria is compared with the cost of grid extension over a distance of 1.8 km. Comparison is also made with the centralised diesel generator power supply option. In addition, the costs of decentralised PV home systems are compared with those of decentralised gasoline generator systems. For all the systems, the initial capital costs and the life cycle costs over a 20-year life cycle are reported. Sensitivity analysis was performed using variations in module costs, diesel fuel prices and grid extension distance. The results suggest that PV has a remarkable potential as a cost-effective option for low-power electrical energy supply to the rural communities in the country.
Selenium (Se) is a promising cathode material in high-energy batteries. However, the polyselenides shuttle effect and large volume change of Se upon cycling as well as the poor ionic and electronic conductivity of Se undermine its cycling and rate performance. Herein, we report a novel Se-based cathode material in which Se is fully encapsulated and attached to the inner shell of hollow-core nitrogen-doped carbon (CNx) nanobelts forming hollow double-shell Se@CNx nanobelts with a well-defined inner-void volume. Such novel electrode material could accommodate the large volume variation of Se upon cycling and facilitate electron and ion transfer while providing a physical entrapment for the Se and polyselenide intermediates, thereby producing large capacity, high rate capability and long-lifespan. With a large Se content of 62.5wt% and areal mass loading of 3.0mgcm−2, the freestanding and binder-free Se@CNx cathode comprising of intertwining and interpenetrating hollow double-shell Se@CNx nanobelts could deliver a high capacity of 608.8mAhg−1 at a density of 675mAg−1 and the cycle stability is maintained for over 400 cycles with only 0.06% capacity decay per cycle. When the current density is increased 20 times from 80 to 1600mAg−1, 70% reversible capacity is retained.
In order to produce thin films of crystalline V2O5, vanadium metal was thermally oxidised at 500°C under oxygen pressures between 250 and 1000mbar for 1–5min. The oxide films were characterised by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). The lithium intercalation performance of the oxide films was investigated by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS). It was shown that the composition, the crystallinity and the related lithium intercalation properties of the thin oxide films were critically dependent on the oxidation conditions. The formation of crystalline V2O5 films was stimulated by higher oxygen pressure and longer oxidation time. Exposure for 5min at 750mbar O2 at 500°C resulted in a surface oxide film composed of V2O5, and consisting of crystallites up to 200nm in lateral size. The thickness of the layer was about 100nm. This V2O5 oxide film was found to have good cycling performance in a potential window between 3.8 and 2.8V, with a stable capacity of 117±10mAh/g at an applied current density of 3.4μA/cm2. The diffusion coefficients corresponding to the two plateaus at 3.4 and 3.2V were determined from the impedance measurements to (5.2 and 3.0)×10−13 cm2 s−1, respectively. Beneath the V2O5 layer, lower oxides (mainly VO2) were found close to the metal. At lower oxygen pressure and shorter exposure times, the oxide films were less crystalline and the amount of V4+ increased in the surface oxide film, as revealed by XPS. At intermediate oxygen pressures and exposure times a mixture of crystalline V2O5 and V6O13 was found in the oxide film.
The objective of this study was to investigate the pattern of enzymatic activities, environmental genotoxicity and cytotoxicity in flounder, Platichthys flesus, from the Polish coastal area of the Baltic Sea. Fish were sampled in different contaminated sites in the Gulf of Gdansk and in a reference area outside the gulf. The activities of acetylcholinesterase (AChE), glutathione s-transferase (GST), catalase (CAT), alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatine kinase (CK), lactate dehydrogenase (LDH), were studied, as well as the frequency of micronuclei, nuclear buds and fragmented-apoptotic cells. A higher mean activity level of muscular AChE and a lower activity level of hepatic GST were evident in samples taken from the reference site, relative to those found in the gulf. Modeled CAT activity (in both liver and gill tissue), blood plasma LDH and CK activities were all significantly higher in flounder collected at locations within the Gulf of Gdansk than at the reference site. No statistically significant alterations were observed in the activities of ALT and AST in the blood plasma of flounder in this study. Fish collected from a location at the mouth of the Vistula River showed the highest hepatic GST and CAT, the highest gill CAT activity, and the highest frequency of blood micronuclei, nuclear buds and fragmented-apoptotic cell inductions, as well as the lowest level of blood plasma CK. The present study confirms that compared to fish from the reference area, flounder from the Gulf of Gdansk clearly demonstrate a different enzyme activity, genotoxicity and cytotoxicity biomarker response pattern.
A Si3N4/graphene composite is designed as an interlayer for a carbon-nanotubes/sulfur cathode to improve electrochemical performance of lithium-sulfur batteries. In the interlayer, Si3N4 nanoparticles suppress the migration of the dissolved polysulfides and graphene sheets construct a 3-dimensional charge-transfer network. The carbon-nanotubes/sulfur@Si3N4/graphene cathode delivers an initial discharge capacity of 1334.7 mAh g−1 at 0.1 C and retains a capacity as high as 745.8 mAh g−1 after 200 cycles, with a capacity fade ratio of 0.22% per cycle. The cathode shows good cycling life, delivering a discharge capacity of 413.3 mAh g−1 for 1 C after 1000 cycles. According to the results of density functional theory calculation, the anchoring of the Si3N4/graphene interlayer to lithium polysulfide can be attributed to a coefficient chemical binding of Li-N and Si-S bonds generating from electronic conjugation effect between the Si3N4 supercell surface and the polysulfides. Generally, the improvement in electrochemical performance originates from the enhancements in Li+ diffusion coefficient and charge transfer, and from the restraining of the shuttle effect of the dissolved lithium polysulfide as a result of the Si3N4/graphene interlayer.
The synthesis and electrochemical properties of a lithium manganese spinel, a LiMn2O4 film and a LiMn2O4/polyaniline (PAni)/PVDF composite film were investigated. The materials were characterized using X-ray diffraction, differential thermal analysis, scanning electron microscopy and BET surface area analysis. The intercalation/deintercalation lithium was investigated using electrochemical impedance spectroscopy, cyclic voltammetry and charge/discharge cycles. The use of PAni as an electronic conductor and electroactive material optimized the process of lithium intercalation/deintercalation in this film. The stabilized lithium extraction capacity of the LiMn2O4/PAni/PVDF composite was significantly higher than for the LiMn2O4 film (138 and 52mAhg−1, respectively).