Today, a considerable effort is being made worldwide to develop inorganic all solid-state batteries (ASSB) that provide greater safety and energy density than conventional Li-ion batteries. The development of such ASSBs is limited by the processing of the inorganic active materials (AM), electrolyte and electronic additives. Indeed, the electrodes are composites that must be compact with intimate and stable interfaces between the different materials to allow a reversible charge transfer, which is generally realized by high temperature sintering process. In addition, a full battery is composed of two composite electrodes sandwiching the ceramic electrolyte with again the need of forming low impedance interfaces. Therefore, the direct realization of inorganic ASSB corresponds to the assembly of multi-materials by co-sintering which must take into account several locks: compatible materials in terms of "sintering windows" (chemical compatibility, sintering temperature and coefficient of thermal expansion); cohesive and intimate interfaces between the materials to ensure a good mechanical hold and to get low resistance for the interfacial charge transfer; finally a self-supported batteries with high areal capacity. In this context, our main objective is to demonstrate the feasibility of assembling a functional prototype of Li-ion ASSB based on a new ultra-fast sintering method called (Electrochemical) Flash Sintering (EFS) that allows a full preform sintering in few seconds, which would renew the field and open new paths for the development of such safe and high energy density technology. Flash Sintering brings a different perspective to the selection of materials for sintering of a multi-layer material. Indeed, the first criterion for flash sintering is the electrical behavior, in particular the conductivity of each material, which determines the sintering conditions. This project proposes the development of a promising process through a fundamental approach coupling the preselection and synthesis of the materials, understanding of the electrochemical and physicochemical mechanisms governing heating, interface formation and densification. Before obtaining operational prototype of Li-ion ASSB that operates reversibly for 100 cycles at RT with at least an areal capacity of 5 mAh/cm2, several challenges have to be tackled. They concern 1/ the choice of the materials, 2/ the optimization of the EFS process parameters together with the formulation of the composite electrodes and the geometrical parameters of the ASSB, 3/ the reversibility of the electroactive interfaces together with their mechanical integrity along cycling. To solve these issues we have planned 4 WPs that corresponds to the different skills of the partners: - WP1: Materials synthesis and characterization. Different types of active materials and electrolytes with as first criteria of choice the thermal stability and the compatibility of the structures will be synthetized by CRISMAT. - WP 2: Flash electrochemical sintering. This central WP will be dedicated to the manufacturing of ASSB in a single step by EFS, controlling the flash phenomenon (thermal runaway) and exploring the relationship between temperature, microstructure, conductivity and thermal production by Joule effect by relying on the great expertise of two partners LEPMI and SIMAP on this technique. - WP3: Modeling densification along EFS. Modeling of heating and sintering under electric current will be carried out at SIMAP using COMSOL finite element code at macroscopic scale. This will help to optimize the electrode formulation, the AASB geometrical parameters, and the process parameters. - WP4: Advanced electrochemical characterizations. A new methodology will be developed to analyze operando the charge transfer processes trough the compact along the flash. The electrochemical behavior and the performance of the ASSB produced in WP2 will be deeply characterized thanks to the LEPMI facilities.

R&D on anion exchange membrane fuel cells (AEMFCs) has shown tremendous progress in recent years, AEMFCs reaching now high power densities with catalysts based on platinum group metals (PGMs). While AEMFCs offer the long-term perspective to switch to PGM-free catalysts due to the high-pH environment, high performance AEMFCs with PGM-free catalysts at both the cathode and anode still needs to be realized. In addition, the chemical stability of AEMs and anion-exchange ionomers is still insufficient. In the DEEP project, novel AEMs and ionomers with improved stability will be developped as well as novel anode and cathode catalysts free of PGM. Down-selected materials will be tested in AEMFC for their initial performance and also for durability testing. DEEP is a collaborative project between 2 academic partners and one partner from the private sector.

All solid-state batteries based on thiosulfate solid electrolyte hold the promise of safer and more energetic batteries, especially once coupled to Li metal anode and high voltage cathodes. Unfortunately, it was demonstrated in the literature that their electrochemical stability window is far from optimal being very narrow (less than 1V). This is causing severe chemical degradation upon oxidation/reduction of the solid electrolyte, showing that the solid electrolyte is a very active player in the solid-state batteries. The decomposition products generated during oxidation/reduction are causing drastic increase in cell resistance as well as some structural/chemical changes both hindering the long-term cycling of solid-state batteries. On top of that, the mechanical stability of the solid-state batteries is also questioned, as during cycling, the electrode breathing will lead to volume changes generating stress i) in the composite electrode materials, ii) at the interfaces, and iii) in the electrolyte. The stress propagation will be soon translated into fractures at all pre-cited levels, affecting the lithium transport mechanism within the cell causing premature cell failure. As described in the literature, this chemo-mechanical degradation looks unavoidable. However, the literature is relying on the investigation of half-cells/full-cells to explain the chemo-mechanical degradation, but the solid electrolyte alone and especially its sintering/shaping could also be the main responsible of most of the pre-cited issues. Poor sintering, as an example, promotes chemical degradation and voids propagation, thus, getting a deep understanding of the sintering process prior to any electrochemical cycling is of utmost importance. We propose a multiscale approach based in operando characterizations at the laboratory scale and at large scale facilitate (synchrotron and neutrons) to fully understand the sintering process of the electrolyte and in particular to establish the relationship between structural/chemical/morphological/electrochemical parameters as a function of the pressure/temperature. To apply this methodology, novel special electrochemical cells will be developed to perform advanced operando-based techniques. Neutron diffraction will be used to follow the structural evolution during sintering process as a function of temperature/pressure, whereas X-ray tomography and FIB-SEM will be employed to follow the evolution of the porosity as a function of the pressure/temperature. Quasi elastic neutron scattering (QENS) owing to the contrast of lithium isotopes will provide information about Li ion transport whereas chemical decomposition will be investigated by X-ray absorption spectroscopy, etc. Once the sintering process will be fully understood, the solid electrolyte fully optimized will be then transferred to half-cell configuration (vs. Li metal) and the same methodology will be applied. Neutron imaging technique will be added to the pool of operando techniques to follow the Li ion transport as a function of cell cycling. Results from morphology/structure/chemistry gathered at this stage will be used to develop proper coating strategy and buffer layer to ensure electrochemical/chemical/morphological/structural stability. Again, once this goal will be reached, full cell investigation combining high voltage cathode vs. Li metal will be undertaken following the same operando-based approach. The results collected and obtained through this OpInSolid project will shed light on a forgotten player, the solid electrolyte. Based on the outcome, several strategies will be developed to tackle chemo-mechanical issues in sulfide-based solid state batteries.

Within the context of energy shift towards a decrease in the contribution of fossil fuels, the development of new stationary energy storage systems is mandatory. Indeed, the intrinsic intermittent and variable nature of renewable energy sources, such as windmill and photovoltaic, require energy storage. Redox-flow batteries, allowing a decoupling of energy and power, are well adapted to such requirements. As a matter of fact, this technology presents advantages as compared to Li-ion systems presently under development for such applications, in particular for security and recyclability issues. However, the most advanced redox-flow batteries (Vanadium redox-flow batteries, studied since the 80’s) remain expensive with limitations in terms of stability and capacities. The present project aims at developing a full redox-flow battery, based on the flow of redox-mediators based aqueous solutions (pH around 7), using sodium insertion materials immobilized in the battery tanks. The use of these insertion materials will allow an increase in the energy density of these systems, and thus to potentially reduce their size. These materials will be free of toxic or expensive metallic element. To perform these research studies, we created a multidisciplinary team which will allow to break the technological locks related to the development of such innovative and performing systems. The project partners will pursue in particular the study and development of a pilot battery so as to demonstrate the potentialities of this approach for electrochemical energy storage at large scale (coupling with windmill and photovoltaic systems), with storage time of the order of a dozen hours.

Proton Exchange Membrane Fuel Cells (PEMFC) are ecologically clean and efficient energy converters, whose power ranges allow their utilization in different domains, mobile, transport and stationary applications. Nevertheless their development in a large scale needs further improvements, specifically regarding lifetime. PEMFC lifetime is particularly linked to the cathode carbonaceous support degradation. To relieve such a major problem, SURICAT aims at developing new catalyst supports, without any carbon, based on metal oxides. Such supports will have to fulfill at least 4 essential criteria: electronic conductivity, possible synthesis of electrochemically active electrocatalyst, corrosion resistance in PEMFC operating conditions and adapted morphology for electrode shapping and fuel cell operation. Two oxides have been selected on the basis of promising preliminary works: titanium dioxide (TiO2) and tin dioxide (SnO2). Their electronic conductivity will be increased by doping (V, NB or Ta) or post-treatment favoring the creation of oxygen vacancies. They will be synthesized following different synthesis routes in order to evaluate the influence of the morphology (spherical particles vs. fibers vs. aerogels) on the catalyst deposition and electrode preparation, on the charge carriers’ mobility as well as on mass transfers through the catalytic layer. A selection process based on the four selected criteria (conductivity, electrochemical activity, corrosion resistance and morphology) will be followed all along the elaboration process (support matrix, electrocatalysts, catalytic layer), through a panel of physicochemical and electrochemical characterizations. The selected metal oxides will then be utilized to prepare Membrane-Electrodes Assemblies (MEAs), characterized on single cell test bench in order to evaluate their performances and, thanks to accelerated ageing tests, the durability of the new supports. The performances of the electrocatalysts composed of metal oxides supported Pt nanoparticles (Pt/MOx) will be compared to those of conventional high specific surface area carbon blacks supported electrocatalysts (typically TKK TEC10E40E). Finally, new promising supports, showing better performances (power density and lifetime) than commercially available carbon blacks, will integrated and evaluated in small portable devices.