Advanced design of a x-ray absorption spectroscopy setup for measuring transition metals speciation in molten carbonates, hydroxides and hydrogenosulfates.

Battery recycling is currently becoming a crucial issue. One possible treatment path involves the use of molten salts. A mechanistic understanding of the underlying processes requires being able to analyze in situ speciation in molten salts at various temperatures. This can be advantageously achieved using x-ray absorption spectroscopy, the use of Quick-EXAFS facilities being particularly appropriate. Consequently, this paper presents the design and development of a new setup allowing carrying out Quick-EXAFS experiments in oxidizing molten salts at high temperatures. We describe the different components of a cell and the performance of the heating device. We illustrate the capabilities of the setup by analyzing the temperature evolution of Co speciation upon dissolution of LiCoO2, a typical battery electrode material, in molten carbonates, hydroxides, and hydrogenosulphates.

Transport Properties of Li-TFSI Water-in-Salt Electrolytes.

Water-in-salts are a new family of electrolytes that may allow the development of aqueous Li-ion batteries. They have a structure that is reminiscent of ionic liquids, and they are characterized by a high concentration of ionic species. In this work, we study their transport properties and how they evolve with concentration by using molecular dynamic simulations. We first focus on the choice of the force field. By comparing the simulated viscosities and self-diffusion coefficients with experimental measurements, we select a set of parameters that reproduces well the transport properties. We then use the selected force field to study in detail the variations of the self and collective diffusivities of all the species as well as the transport number of the lithium ion. We show that correlations between ions and water play an important role over the whole concentration range. In the water-in-salt regime, the anions form a percolating network that reduces the cation-anion correlations and leads to rather large values for the transport number compared to other standard electrolytes.

Characterization of porous structure through the dynamical properties of ions confined in sulfonated polyimide ionomers films.

The structure of sulfonated PolyImide (sPI) ionomer membrane has been investigated via the transport properties of ions confined inside. Transport coefficients of N(CH(3))(4)(+) and Na(+) ions have been determined by several techniques in order to get a range of time/space scale as wide as possible: a method using radiotracers, conductivity, pulsed field gradient NMR and NMR quadrupolar relaxation rates determination. For N(CH(3))(4)(+), the self-diffusion has been measured in the direction of membrane plan (parallel) and in the perpendicular direction (transverse), whereas for Na(+) only transverse self-diffusion has been measured. The conductivity of both ions has been measured in the transverse direction. The results show a anisotropic and multiscale structure with a separation phase between hydrophilic and hydrophobic domains that is not well-defined.