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A simplified method is presented to extract the transport parameters of a liquid electrolyte solution from an experiment in a four-electrode cell. By observing that both polarisation and relaxation tend exponentially to a finite value with the same time constant, it becomes possible to precisely evaluate the limiting voltage attained upon polarisation though no steady state can be reached in practice, and use this input to evaluate the cation transference number as a function of the thermodynamic factor. This procedure simplifies the data analysis by avoiding complete fitting of the polarisation with a complicated numerical model. Such approach can favour the deployment of the four-electrode method to evaluate electrolyte transport parameters, which are crucial for the development of better performing batteries.

A comparative study of the reduction of TiS2 in diverse electrolyte formulations involving Ca(BF4)2 and Ca(TFSI)2 salts was carried out at different temperatures (from 25 °C to 100 °C). While for the former salt intercalation of calcium is only observed at high temperatures, calcium intercalated phases are also observed for the latter even at room temperature. The nature of the electrolyte does also have an impact on the relative amounts of the phases formed. Since Ca(TFSI)2 based electrolytes do not enable calcium plating, cycling was attempted using activated carbon as counterelectrode, and the reversibility of the process was ascertained. Even if corrosion of stainless steel current collectors and side reactions do still prevent proper cyclability, the results achieved should contribute to the establishment of reliable and viable cell set-up and methodology for the unambiguous study of the intercalation process in multivalent battery systems.

In this work, aprotic and protic ionic liquid (IL)-based electrolytes designed for calcium-based energy storage systems are investigated. We have shown that these electrolytes display good transport properties and electrochemical stabilities comparable with those of IL-based electrolytes proposed for lithium and sodium-based systems. The use of these electrolytes in electrochemical double layer capacitors (EDLCs) leads to the realization of devices displaying good capacitances paired with a high reversibility and stability. Their use in combination with TiS2 cathode appears more problematic as the cation of the ILs is inserting in the layered structure of this material during the charge process. In this latter case a careful design of the cation appears necessary to guarantee selective insertion of Ca2+ and reversible charge-discharge process.

While less mature than Li-ion battery, technologies based on Na, K, Mg and Ca are attracting more and more attention from the battery community. New material (cathode, anode or electrolyte) testing for these post Li systems commonly involves the use of an electrochemical setup called half-cell in which metal counter and reference electrodes are used. Here we firstly describe the different issues that become critical when moving away from Li with respect to the cell hardware (cell design, current collector, separator, insulator) and the nature of counter and reference electrodes. Workarounds are given and a versatile setup is proposed to run reliable electrochemical tests for post Li battery materials in general, in a broad range of electrolyte compositions.

Sodium-ion batteries (SIBs) are currently being considered for large-scale energy storage. Optimization of SIB electrolytes is, however, still largely lacking. Here we exhaustively evaluate NaPF6 in diglyme as an electrolyte of choice, via both physicochemical properties and extensive electrochemical tests including half as well as full cells. Fundamentally, the ionic conductivity is found to be quite comparable to carbonate based electrolytes and to obey the fractional Walden rule with viscosity. We find Na metal to work well as a reference electrode and the electrochemical stability, evaluated potentiostatically for various electrodes and corroborated by DFT calculations, to be satisfactory in the entire voltage range 0–4.4 V. Galvanostatic cycling at C/10 of half and full cells using Na3V2(PO4)3 (NVP) or Na3V2(PO4)2F3 (NVPF) as cathodes and hard carbon (HC) as anodes indicates rapid capacity fading in cells with HC anodes, possibly originating in a lack of a stable SEI or by trapping of sodium. Aiming to understand this capacity fade further, we conducted a GC/MS analysis to determine electrolyte reduction products and to propose reduction pathways, concluding that oligomer and/or alkoxide formation is possible. Overall, the promising results should warrant further investigations of diglyme based electrolytes for modern SIB development, albeit avoiding HC anodes.

Na-ion batteries have regained attention because they offer sustainability advantages over the Li-ion technology, hence their interest for massive electrochemical storage. Although the Na-ion electrochemistry is analogous to that of the Li-ion concept, there are a few notable differences such as the stability of carbonated-based electrolytes toward the Li or Na metal anodes. Herein we report on the positive effect of FEC as electrolyte additive on the efficiency of Na-half cells which unfortunately comes with a side effect involving the sudden onset of polarization during discharge at unpredictable capacity values. We show that these anomalies, associated to an inefficient plating-stripping at the sodium metal anode, do not appear in full Na-ion cells. Therefore, FEC-based electrolytes are not the panacea and alternative additives must be sought to enable building of reliable half cells with metal anodes.

La transcription des symboles et des caractères spéciaux utilisés dans la version originale de ce résumé n’a pas été possible en raison de limitations techniques. La version correcte de ce résumé peut être lue en PDF. Les piles à acide formique direct utilisent à l’heure actuelle des membranes de Nafion comme électrolyte. Dans ce matériau biphasé, l’eau dans la phase hydrophile est le support à la conduction des protons. Les combustibles liquides comme l’acide formique, miscibles avec l’eau, sont eux aussi transportés d’une électrode à l’autre dans cette phase hydrophile. Cela entraîne d’importantes pertes de rendement limitant les performances et le développement des piles à combustible liquide direct. Afin d’améliorer la sélectivité des membranes, une approche consiste à incorporer une charge conductrice protonique dans le Nafion. Le dioxyde de ruthénium hydraté, RuO2-xH2O, est un matériau performant comme électrode de supercondensateur du fait que les protons peuvent diffuser en son volume. L’étude présente a pour but d’exploiter cette conductivité protonique de RuO2-xH2O pour application dans les électrolytes de piles à combustible. À cette fin, des membranes composites de polypropylène et RuO2-xH2O ont été préparées. Deux grandeurs ont été mesurées sur ces membranes : leur perméabilité et leur conductivité ionique. L’optimisation de l’analyse des mesures de perméabilité ex-situ a permis d’accéder simultanément aux deux coefficients de diffusion de l’eau et de l’acide formique dans les membranes. Dans le Nafion, ces coefficients sont de 12 10-6 cm2 s-1 pour l’eau et 6,8 10-7 cm2 s-1 pour l’acide formique. Le coefficient de diffusion de l’acide formique dans les membranes composites est de 0,8 à 8 10-7 cm2 s-1, du même ordre de grandeur que celui du Nafion. Le coefficient de diffusion de l’eau est inférieur à 10-6 cm2 s-1 soit dix fois plus faible que dans le Nafion. Concernant les propriétés électriques, un modèle tridimensionnel a été mis en place pour décrire