WP1:Synthesis and characterization of cationic/anionic PILs and SiNPs
WP1 will focus on the design and preparation of the building blocks necessary for the formation and investigation of DIGs within WP2, i.e. cationic/anionic PILs and SiNPs, by combining the complementary expertise of LIST and IMP partners. Thus, a first task will be dedicated to the synthesis of the imidazolium- and 1,2,3-triazolium-based cationic PILs having highly delocalized bis(trifluoromethylsulfonyl)imide (TFSI) counter-anions. The second task will include the preparation of anionic PIL copolymers with oligo(ethylene glycol) monomethyl ether methacrylate and a second methacrylate carrying pendent TFSI anions and 1-ethyl-3-methyl-imidazolium (EMIM) counter-cations. The third task will involve the synthesis of both negatively (i.e. TFSI) and positively (i.e. imidazolium) charged SiNPs by chemical modification of the surface of fumed silica through the introduction of ions via flexible spacers using sol-gel chemistry. Finally, the fourth task will involve thorough structural and physical characterization of all organic and inorganic ionic building blocks prepared within this WP. The chemical structures of PILs and SiNPs are suggested in such a way that the combination of each oppositely charged building block will provide the in situ generation of EMIM TFSI, one of the best ionic liquids known in terms of the balance of ionic conductivity (i.e. 10-2 S/cm at 30 °C) and electrochemical stability (ca. 4 V vs Li/Li+).
WP2:Preparation and understanding structure/properties correlations of DIGs
WP2 is dedicated to the formulation, processing and thorough characterization of DIGs. A first task will be devoted to the investigation of the processing conditions (i.e. effect of solvent nature, concentration, shear, temperature and mixing time) on the properties of the resulting DIGs (i.e. viscoelasticity, tensile properties and ionic conductivity). This initial task will rely on the thorough study of a model polycation/polyanion organic system (e.g. cationic PIL2 and anionic PIL4) using rheology and broadband dielectric spectroscopy. A second task will be devoted to the understanding of the structural parameters influencing the properties of DIGs (i.e. ratio of cationic and anionic groups, molar mass of the building blocks, fraction of charged monomer in the anionic PIL copolymer, organic vs hybrid alloys…). This detailed study will establish the processing/structure/properties relationships of this innovative approach in order to obtain DIGs with most robust mechanical properties, strain and temperature stabilities, and highest ion conducting properties (up to 10-4 – 10-3 S/cm @RT). Finally this approach using optimal structure/processing conditions will be extended to the elaboration of supported quasi-solid electrolyte layers from different deposition methods, with varying thicknesses on various substrates (glass, silicon wafers and typical electrodes used for supercapacitors such as aluminum, stainless steel).
WP3:Elaboration of Supercapacitors and their testing
WP3 focuses on the (i) synthesis and preparation of reduced graphene oxide (RGO)|DIG mixtures, (ii) creation of planar electrodes from these mixtures and their characterizations (electrochemical, mechanical, morphological, etc.) and (iii) assembly of the solid-state SCs combining optimized electrodes and DIG-based electrolytes selected from WP2. Reduced graphene oxide (RGO), selected for its ability to provide high energy density in SCs, ready availability and low cost vs. carbon nanotubes, will be intercalated with DIGs (RGO|DIG) by reducing GO in the presence of cationic PIL and subsequent addition of anionic PIL to the organic dispersion (task 3.1 and Fig. 6). Intercalation is critical as it provides an essential ion source within the electrodes enabling ion conduction throughout the assembly (electrode/electrolyte/electrode)[28] and enhanced adhesion between electrodes and electrolyte due to dynamic ionic crosslinking at the RGO|DIG//DIG interface. Such RGO|DIG active materials with in-situ generated EMITFSI ionic liquid will be obtained as mixtures in organic solvent (task 3.1, Fig. 6), whereupon the planar RGO|DIG electrodes will be prepared from these mixtures by casting / spraying onto aluminum foil current collector. (task 3.2). RGO|DIG electrodes will be characterized electrochemically and mechanically and the highest performing will be selected for SC assembly (task 3.3). Task 3.3 will be split into two parts, where the first step will consist of a proof-of-concept, with SCs produced in coin-cell form with a planar trilayer configuration using optimized RGO|DIG electrodes and DIG solid electrolytes as determined in WP2. The assembled RGO|DIG//DIG//RGO|DIG SCs will be evaluated in terms of specific energy/power performance and on the second step the optimum configuration will be selected for scale-up and assembly of prototype pouch-cell SCs with 5x5cm² surface area.
