New eco-friendly low-cost binders for Li-ion anodes

In the production of commercial Li-ion batteries, the active materials slurries are generally prepared using polyvinylidene fluoride (PVdF) as binder because of its good adhesion properties and electrochemical stability. Unfortunately, there are some disadvantages related to the use of PVdF: the most important is the use of toxic and environmentally unfriendly solvents, such as N-methyl-pyrrolidone (NMP), and the second is the high costs. In the light of these considerations, it seemed straightforward to investigate the suitability of some water-soluble, inexpensive, and eco-friendly materials to test as alternative binders (sodium alginate, chitosan tragacanth gum, gelatin). The rheological properties of these materials have been investigated in addition to the electrochemical characterization. Furthermore, graphite electrodes with PVdF, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) binders have been considered for sake of comparison. We found that some of these water-soluble binders, besides good electrochemical performances, showed a high adhesion to the current collector and a good electrochemical stability under the experimental conditions employed, which makes them interesting for the next generation of Li-ion batteries.     

A new generalization of Hermite’s reciprocity law

Given a partition \(\lambda \) of n, the Schur functor \({\mathbb {S}}_\lambda \) associates to any complex vector space V, a subspace \({\mathbb {S}}_\lambda (V)\) of \(V^{\otimes n}\). Hermite’s reciprocity law, in terms of the Schur functor, states that \({\mathbb {S}}_{(p)}\left( {\mathbb {S}}_{(q)}({\mathbb {C}}^2)\right) \simeq {\mathbb {S}}_{(q)}\left( {\mathbb {S}}_{(p)}({\mathbb {C}}^2)\right) . \) We extend this identity to many other identities of the type \({\mathbb {S}}_{\lambda }\left( {\mathbb {S}}_{\delta }({\mathbb {C}}^2)\right) \simeq {\mathbb {S}}_{\mu }\left( {\mathbb {S}}_{\epsilon }({\mathbb {C}}^2)\right) \).     

Coupling atomistic and finite element approaches for the simulation of optoelectronic devices

Multiscale methods coupling quantum mechanical/atomistic models such as envelope function and tight binding approaches with continuous media models e.g. for strain or electronic transport are very useful for an accurate simulation of modern and emerging electronic and optoelectronic devices based on nanostructured active regions. We present simulations using TiberCAD whose main focus is on providing an integrated multiscale/multiphysics simulation environment.     

UV-cured polymer electrolyte membranes for Li-cells: Improved mechanical properties by a novel cellulose reinforcement

One of the main drawbacks that restricts the practical application of gel-polymer electrolytes is the inferior mechanical performance compared to other available systems. In this work, we have reinforced UV-cured methacrylic membranes with cellulose. To enhance its compatibility with the polymer matrix, cellulose is modified by UV-grafting poly(ethylene glycol) methyl ether methacrylate on it. Excellent mechanical properties are obtained and good ionic conductivity values are observed, enlightening that this kind of membrane is an interesting candidate for future applications as thin gel-polymer electrolyte in flexible lithium batteries.     

Mechanochemical synthesis and electrochemical properties of nanostructured electrode materials for Li ion batteries

We focus on the synthesis by ball milling and on the electrochemical characterization of nanocrystalline bimetallic and composite materials to be employed as anodes in Li ion batteries. Ni₃Sn₄ and Ni₃Sn₂ based compounds were obtained by ball milling of three different Ni–Sn mixtures. The properties of the resulting anodes for Li ion batteries were evaluated as a function of composition. Moreover, a biphasic system is presented, with CoSn₂ and CoSn type structures, arising from the synthesis of the Sn₃₁Co₂₈C₄₁ composition. When cycled in a Li cell, this material showed a high reversible specific capacity, about 450 mA h g⁻¹, and a very good electrochemical and structural stability, making it of interest for application purposes. Contribution to the Fall Meeting of the European Materials Research Society, Symposium D: 9th International Symposium on Electrochemical–Chemical Reactivity of Metastable Materials, Warsaw, 17th–21st September, 2007.     

Calculation of optical properties of a quantum dot embedded in a GaN/AlGaN nanocolumn

The TiberCAD simulation tool for calculation of optical and electronic properties of nanostructured devices has been used to study spontaneous emission of a GaN quantum dot embedded in an AlGaN nanocolumn. Macroscopic calculations provide corrections to the quantum calculation, showing the role of strain and the polarization field in spectra and the electron and hole states arrangement.     

New sol-gel synthetic route to phospho-olivines as environmentally friendly cathodes for Li-ion cells

A new sol-gel synthetic route was developed to prepare single-phase phospho-olivines LiMPO4 (M = Fe or Mn), potential cathode materials for the next generation of Li-ion secondary batteries. Triethyl phosphite was used as phosphate organic precursor, with absolute ethanol as solvent. The sol-gel synthesis ensures homogeneity of the precursors at the nanometric scale and improved reactivity, allowing to obtain very small agglomerates and crystal grain size. Several carbon sources were used in order to improve the electrochemical performances of the samples. Galvanostatic cycling tests of the cathodic materials were made on coin cells with Li metal as anode in order to study the influence of the synthesis and the structural-morphological characteristics on the electrochemical performance of the phosphate/C composite.     

Optimisation of some parameters for the preparation of nanostructured LifePO4/C cathode

LiFePO₄/C powders have been synthesised by an easy and inexpensive mild hydrothermal method in the presence of an organic surfactant compound [hexadecyltrimethylammonium bromide (CTAB)] previously developed. The samples have been synthesised with different amounts of CTAB, and the effect of this parameter on their structural characteristics and electrochemical behaviour has been investigated. The processing of the high-resolution diffraction data in a Rietveld refining analysis and the HRTEM observations, previously not available, has put in evidence the high purity of the samples prepared and the good quality of the carbon layer covering the grains. Such layer, obtained during the firing step of the preparation in N₂ atmosphere, is very important to enhance the electronic conduction of the electrode. The sample high purity and the conduction enhancer carbon layer, along with the low grain size and high surface area, properties already put in evidence, are obtained to the maximum degree only for a sample prepared with a certain quantity of surfactant. The investigations on samples with very low and with the maximum CTAB content found out the best performing sample confirming the previous results. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, France, Sept. 9–15, 2007     

A solid-state V NMR characterization of vanadium sites in LiCoxNi1−xVO4

LiCo_xNi_1−xVO₄ compounds (x=0, 0.2, 0.5, 0.8, 1.0) have been prepared for lithium ion batteries by different preparation methods, namely, wet-chemistry (WC) and solid-state (SS) routes. ⁵¹V nuclear magnetic resonance (NMR) has been employed to accurately assess the vanadium environments in these materials and results show that vanadium atoms are distributed in octahedral and tetrahedral sites. The fractions of vanadium atoms in tetrahedral/octahedral sites depends on composition and sample preparation conditions. The tetrahedral site, which is particularly dominant in samples produced via the WC route, is more affected by paramagnetic interactions and its ⁵¹V NMR spectrum is essentially Gaussian in shape. The octahedral site, on the other hand, exhibits first-order quadrupolar broadened satellites. Even though tetrahedral sites for a given x are comparable for WC and SS materials, there are some differences amongst octahedral environments, namely in the distributions of quadrupolar broadened satellites. The larger satellite distribution observed for WC materials is indicative of a larger distribution of structural defects for these as compared to SS materials.