RESUMEN
Having in mind the remarkable economic and environmental issues involved in the presence of nickel and cobalt metals in electrode compositions, new Na0.67Mg0.05Fe0.1NixMn0.85-xO2 (x=0.0, 0.05, 0.1, 0.15) with a P2 type layered structure, are synthesized to be essayed as positive electrodes in sodium-ion batteries. The sol-gel route here proposed favors the obtention of highly pure and crystalline samples with a homogeneous distribution of the constituting elements. Both galvanostatic and voltammetric tests reveal a superior electrochemical behavior for the Ni-free sample, which delivers 94â mA h g-1 at 5C. This excellent performance is associated with a good kinetic response in terms of low charge and discharge hysteresis, high Na+ diffusivity, and low cell resistance. Ex-situ measurements evidenced the combined contribution of both the reversible electrolyte insertion and the formation of peroxo species. These advantageous properties allow this electrode to reach a remarkable behavior when is cycled either to low temperatures or high rates.
RESUMEN
The supply of battery-grade nickel to produce positive electrodes of sodium-ion batteries may soon become insufficient. For this reason, it is crucial to find new electrode materials that minimize its use or even fully remove this element from synthesis. We have prepared a Na0.67Mg0.05FexNiyMnzO2 (0 ≤ x ≤ 0.2; y = 0.05, 0.15; 0.6 ≤ z ≤ 0.9) series with low Ni and Fe contents by a single and easily scalable sol-gel method. This procedure yields high-purity and crystalline samples as evidenced by structural, morphological, and spectroscopic studies, including X-ray diffraction, electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical tests showed an exceptional performance for the F0N05 sample with the lowest (Ni + Fe) contents, at 5 C (ca. 100 mA h g-1), and good capacity retention after 100 cycles. This excellent behaviour was also evidenced when cycling at -15 °C. These results were confirmed by electrochemical techniques, such as cyclic voltammetry and impedance spectroscopy, that evidenced a fast exchange of sodium ions due to a significant capacitive contribution and high apparent diffusion coefficients. Post-mortem analysis of the F0N05 electrodes by XRD showed the reversible insertion and the absence of detrimental P2-O2 and P2-P2' transitions, while XPS spectra demonstrated the reversible redox activity of both transition metals and oxygen.
RESUMEN
El objetivo de este estudio fue demostrar el impacto de un programa de intervención basado en la tutoría entre iguales para mejorar la autorregulación del aprendizaje del alumnado universitario de nuevo ingreso, identificando asimismo sus efectos en el alumnado tutor. La muestra estuvo compuesta por 102 estudiantes de nuevo ingreso (51 grupo experimental y 51 grupo control) y 50 estudiantes de último curso de cuatro titulaciones. La autorregulación del aprendizaje se evaluó a través del Cuestionario de Estrategias de Aprendizaje y Motivación. Después de asignar aleatoriamente al alumnado de nuevo ingreso a la condición experimental o control de un diseño cuasiexperimental con grupo control no equivalente mejorado con técnicas de control estadístico, la intervención consistió en 20 sesiones individuales de tutoría altamente estructuradas con el alumnado de nuevo ingreso, dirigidas por el alumnado de último curso o tutor, que fue previamente entrenado para ello en tres sesiones de formación. Los resultados arrojan diferencias estadísticamente significativas en autorregulación del aprendizaje para el alumnado participante.(AU)
The aim of this study was to check the impact of an intervention program based on peer-tutoring on self-regulated learning of freshmen, as well as on peer tutors. The sample consisted of 102 freshmen (51 experi-mental group y 51 control group) and 50 seniors from four different uni-versity degrees. Self-regulated learning was measured by the Motivated Strategies Learning Questionnaire. After assigning freshmen randomly to either the experimental or control condition, the study adopted a quasi-experimental research design with a non-equivalent control group con-trolled by statistical techniques, the intervention consisted of 20 individual tutoring sessions highly structured to freshmen delivered by seniors or tu-tors, after receiving three sessions of training on tutoring. The results yield statistically significant differences in self-regulated learning on participants.(AU)
Asunto(s)
Humanos , Adulto Joven , Ciencias de la Salud , Tutoría/métodos , Estudiantes , AprendizajeRESUMEN
Highly Al-substituted C-coated Na3V2-xAlx(PO4)3 compounds with a sodium superionic conductor structure are synthesized by a single and easily scalable sol-gel route. The effect of the experimental conditions is examined. Their structural, chemical, and morphological features are described. The first-principles method is used to determine the theoretical voltage vs Na content profile during Na extraction. The electrochemical Na extraction is characterized by the presence of two plateaus. The first one at ca. 3.4 V is assigned to the V4+/V3+ redox pair and shows good cyclability. The second plateau at ca. 3.9-4.0 V can be assigned to the V5+/V4+ pair, as evidenced by X-ray photoelectron spectroscopy. This second plateau is less reversible during further discharge.
RESUMEN
Na3V2(PO4)3/C nanocomposites are synthesized by an oleic acid-based surfactant-assisted method. XRD patterns reveal high-purity samples, whereas Raman spectroscopy evidence the highly disordered character of the carbon phase. Electron micrographs show submicron agglomerates with a sea-urchin like morphology consisting of primary nanorods coated by a carbon phase. The electrode material was tested in half and full sodium cells. The electrochemical performance is clearly improved by this optimized morphology, particularly at high C rates. Thus, 76.6 mA h g(-1) was reached at 40C for Na3V2(PO4)3/C nanorods. In addition, 105.3 and 96.7 mA h g(-1) are kept after 100 cycles at rates as high as 5 and 10C. This exceptional Coulombic efficiency can be ascribed to the good mechanical stability and the low internal impedance at the electrode-electrolyte interphase.
RESUMEN
A molecular wiring concept was induced in LiFePO4 cathodes by in battery polymerization methods. This was performed by the addition of alkylthiophene monomers over the LiFePO4-based cathode during the first charging step in lithium test cells. The driving force for the in battery polymerization of the monomers was supplied by the oxidizing current and by the physical contact of monomers with delithiated Li1-xFePO4 formed during the charging of the battery. The resulting molecularly engineered cathodes give higher initial capacity, superior rate capability and improved cyclability compared to the pristine LiFePO4 compound. Further to observe changes in the oxidation state of iron, Mössbauer spectroscopy was employed and the results were correlated with those of impedance spectroscopy, which reveal a significant increase in conductivity during charging. The presented methods provide simple yet effective routes for manufacturing efficient cathode materials at room temperature, without the need of additional oxidizing compounds to carry out the polymerization process and to rival high temperature based carbon coatings.
RESUMEN
Nanocrystalline CoSn with an average crystallite size of 19 nm is obtained at 265 degrees C by following a one-pot method. The structural and electrochemical properties of nano-CoSn are compared to those of micro-CoSn (319 nm) obtained at 500 degrees C. Micro-CoSn has specific capacities below 100 mAhg(-1), but very stable cycling behavior. In contrast, nano-CoSn exhibits reversible specific capacities of over ca. 400 mAhg(-1)in the first cycles, depending on the cycling conditions. The crystalline structure of micro-CoSn is preserved after electrochemical reaction with lithium. Nano-CoSn becomes amorphous upon cycling and a modified 119Sn Mössbauer spectrum corresponding to a LiCoSn nano-alloy is observed.
RESUMEN
Active CuFe(2)O(4) electrode materials for lithium cells are produced by thermal decomposition of a citrate precursor. The precipitation of the metal citrate is carried out by a freeze-drying procedure. A tetragonally distorted spinel structure is prepared by the decomposition of a citrate precursor. Samples free of impurities are obtained depending on the annealing temperature. The sample heated at 800 degrees C performed at 470 mAh g(-1) after 50 cycles. Electron microscopy is used as the ultimate technique to monitor the morphological changes upon the reversible conversion reaction. Detachment of metallic particles from the starting material, the formation of a polymeric organic film, and the subsequent removal on charging are discussed as determining factors in the electrochemical behaviour of this oxide as an electrode versus lithium. The growth of metallic iron aggregates is inferred from the (57)Fe Mössbauer spectra.
RESUMEN
El propósito del estudio fue determinar el impacto de una intervención cognitivo-conductual sobre una muestra de alumnos diagnosticados con TDAH pertenecientes a ocho centros de enseñanza tres públicos y cinco concertados de Educación Primaria de la Provincia de Granada. Para llevar a cabo el estudio, se utilizaron diversas pruebas con las que se evaluó el control inhibitorio, el control perceptivomotor, la memoria y la atención, consideradas como las manifestaciones más comunes del TDAH, en el contexto familiar y escolar. La intervención se basó en la formación de padres y docentes, así como en un posterior entrenamiento específico y directo sobre el alumnado. Los resultados de la intervención, muestran que se han producido mejoras significativas en las conductas problema que presentaban los alumnos, tanto en el contexto familiar como escolar (AU)
The purpose of this study was to determine the impact of a cognitive-behavioural intervention among a sample of students diagnosed with ADHD, belonging to three public and five semi-public Primary Education Schools within the province of Granada. In order to carry out this research several evaluation test were administered to evaluate inhibitory control, motor-perceptive control, memory and attention, considered those as the core features of ADHD, at family and school settings. The intervention consisted of instructing parents and teachers as well as providing training to students. The results show that significant improvement was obtained by students at both family and school settings (AU)
