Eco-Efficient Synthesis of LiFePO4 with Different Morphologies for Li-Ion Batteries

LiFePO4 is presently the most studied electrode material for battery applications. It can be prepared via solution, although it requires well-controlled pH conditions to master the iron valence state in the newly created material. Here we report its synthesis via the use of "latent bases" capable of releasing a nitrogen base upon heating. This way of controlling the reaction pH enables, in the absence of excess Li, the preparation of Fe+3-free LiFePO4 powders having various morphologies and showing good electrochemical performance. This approach is shown to offer great opportunities for the low-temperature synthesis of various electrode materials

Evidence for electronic and ionic limitations at the origin of the second voltage plateau in nickel electrodes, as deduced from impedance spectroscopy measurements

The second plateau occurring during the reduction of the nickel oxyhydroxide electrode (NOE) was studied by impedance spectroscopy on a cell with a pasted electrode prepared from commercial undoped -Ni(OH)2. Measurements were performed at diverse states of reduction and a large variation of impedance upon the transition from the first to the second plateau was observed. This variation mainly takes place at low frequencies and is hence related to ionic diffusion. We observed that the impedance becomes more capacitive on the second plateau meaning that the proton diffusion is limited. These results would be consistent with the gradual formation of an insulating layer of nickel hydroxide at the interface between the NOE and the electrolyte upon reduction. Once this layer becomes compact the ionic diffusion would be hindered and forced to occur through this layer, which could explain the voltage drop observed

Influence of secondary phases during annealing on re-crystallization of CuInSe2 electrodeposited films

Electrodeposited CuInSe2 thin films are of potential importance, as light absorber material, in the next generation of photovoltaic cells as long as we can optimize their annealing process to obtain dense and highly crystalline films. The intent of this study was to gain a basic understanding of the key experimental parameters governing the structural–textural-composition evolution of thin films as function of the annealing temperature via X-ray diffraction, scanning/transmission electron microscopy and thermal analysis measurements. The crystallization of the electrodeposited CuInSe2 films, with the presence of Se and orthorhombic Cu2−xSe (o-Cu2−xSe) phases, occurs over two distinct temperature ranges, between 220 °C and 250 °C and beyond 520 °C. Such domains of temperature are consistent with the melting of elemental Se and the binary CuSe phase, respectively. The CuSe phase forming during annealing results from the reaction between the two secondary species o-Cu2−xSe and Se (o-Cu2−xSe+Se→2 CuSe) but can be decomposed into the cubic β-Cu2−xSe phase by slowing down the heating rate. Formation of liquid CuSe beyond 520°C seems to govern both the grain size of the films and the porosity of the substrate–CuInSe2 film interface. A simple model explaining the competitive interplay between the film crystallinity and the interface porosity is proposed, aiming at an improved protocol based on temperature range, which will enable to enhance the film crystalline nature while limiting the interface porosity

Pseudogap state in slightly doped by aluminium and praseodymium YBa2_2Cu3_3O7−δ_{7-\delta} single crystals with a given topology of plane defects

In present work the conductivity in the basis plane of YBaCuO single crystals slightly doped by Al and Pr with a pre-specified topology of twin boundaries has been investigated. The excess conductivity for the analyzed samples shows dependence like $\Delta\sigma\sim(1-T/T^*)\exp(\Delta_{ab}^*/T)$ in wide temperature range $T_f<T<T^*$, where $T^*$ can be represents as mean field temperature of superconducting transition. The temperature dependence of pseudogap can be satisfactory described in terms of the BCS-BEC crossover theoretical model.Comment: 3 pages, 2 figure

Nanomaterials for Electrochemical Energy Storage: the Good and the Bad

A critical view on the outcome of research in nanomaterials for electrochemical energy storage devices (batteries and supercapacitors) is provided through selected examples. The nano- approach traces back to the early battery research and its benefits realized even before the nano- term was coined. It has enabled important progresses which have translated, for instance, in the possibility of using LiFePO4 as electrode material. On the other hand, the nano- approach has also been oversold at all levels and hence some examples are also shown on the detrimental side effects of the use of nano-materials which should be taken into account if steady progress is to be made that finally results in practical benefits in energy storage devices

Effects of Zn on the grain boundary properties of La2-xSrxCu1-yZnyO4 superconductors

The properties of the grain boundaries (GBs) are of significant importance in high-Tc cuprates. Most large scale applications of cuprate superconductors involve usage of sintered compounds. The critical current density and the ability to trap high magnetic flux inside the sample depend largely on the quality of the GBs. Zn has the ability to pin vortices but it also degrades superconductivity. In this study we have investigated the effect of Zn impurity on the intergrain coupling properties in high-quality La2-xSrxCu1-yZnyO4 sintered samples with different hole concentrations, p (\equiv x), over a wide range of Zn contents (y) using field-dependent ac susceptibility (ACS) measurements. The ACS results enabled us to determine the superconducting transition temperature Tc, and the temperature Tgcp, at which the randomly oriented superconducting grains become coupled as a function of hole and disorder contents. We have analyzed the behavior of the GBs from the systematic evolution of the values of Tgcp(p, y), Tc(p, y), and from the contribution to the field-dependent ACS signal coming from the intergrain shielding current. Zn suppresses both Tc and Tgcp in a similar fashion. The hole content and the carrier localization due to Zn substitution seem to have significant effect on the coupling properties of the GBs. We have discussed the possible implications of these findings in detail in this article. PACS: 74.72.Dn; 74.62.Dh; 74.25.Sv Keywords: Zn doped La214; Critical current density; Grain boundaryComment: To appear in Physica

Macromolecular structural dynamics visualized by pulsed dose control in 4D electron microscopy

Macromolecular conformation dynamics, which span a wide range of time scales, are fundamental to the understanding of properties and functions of their structures. Here, we report direct imaging of structural dynamics of helical macromolecules over the time scales of conformational dynamics (ns to subsecond) by means of four-dimensional (4D) electron microscopy in the single-pulse and stroboscopic modes. With temporally controlled electron dosage, both diffraction and real-space images are obtained without irreversible radiation damage. In this way, the order-disorder transition is revealed for the organic chain polymer. Through a series of equilibrium-temperature and temperature-jump dependencies, it is shown that the metastable structures and entropy of conformations can be mapped in the nonequilibrium region of a “funnel-like” free-energy landscape. The T-jump is introduced through a substrate (a “hot plate” type arrangement) because only the substrate is made to absorb the pulsed energy. These results illustrate the promise of ultrafast 4D imaging for other applications in the study of polymer physics as well as in the visualization of biological phenomena

Non-Equilibrium Ionic Liquid-Electrode Interface at Elevated Temperature and Its Influence on Co2+Reduction Process

Electrodeposition in Ionic Liquid (IL) media is still at its infancy stage. Recently much attention is devoted to exploration of the IL-electrode interface for better understanding of the electrochemical processes at the electrified surfaces. Herein, we provide a new perspective of the temperature-driven IL-substrate interface structuring. We observed an increase in Co2+ reduction kinetics induced by applying a high temperature gradient. In contrast, keeping the cell at a high constant temperature (100°C) leads to slower Co2+ reduction kinetics, it results in a shift of the reduction onset and evolution of the cyclic voltammogram shape with time. We could ascribe these phenomena to the disturbance of the electrochemical double layer (induced by heating) and its further slow reorganization at constant temperature. We showed that such non-equilibrium behavior can be beneficial for the synthesis of metallic thin films from ILs. Electrochemical quartz crystal microgravimetry, impedance spectroscopy, cyclic voltammetry and chronoamperometry were employed within this work