The report outlines activities and results of research carried out on the development of materials and technologies of small electrochemical Storage Systems (SSs), as well as large-scale storage for the national transmission grid.

Activities on electrochemical SSs mainly concern the study, formulation and synthesis of innovative materials and the design and implementation of newdesignof cells.

One activity concerns the commissioning of a new planar-geometry cell for a high-temperature (about 300°C) sodium-nickel chloride battery whose electrodes are liquid metals and the electrolyte is an ion-conductive solid ceramic material (β “alumina). In particular, this job involved the implementation of technological solutions capable of subjecting the cell to charge and discharge cycles with no material loss, starting with an initial, cold filling of electrode materials into a single compartment, as well as the producing β”alumina with new formulations and through a new sintering technique calledSpark Plasma Sintering(SPS).

Another activity is the development of a Sodium Ion Battery (NIB) with a Mxenes (porous lamellar materials) based anode obtained by chemical treatment (exfoliation) of mixed metal carbides (e.g., Ti-Al) belonging to theMAX-phasefamily. In particular, processes were refined to synthesize MAX-phases (via SPS), reduce them to powder of appropriate particle size, and exfoliate them with appropriate HCl and NaF solutions. The MXenes thus produced were then characterised as anodes in coin half-cells, using metallic sodium as a counterelectrode, to ascertain their ability to intercalate Sodium ions. In addition, cathode material was realised that can be combined with MXenes to manufacture a NIB single-cell prototype.

Another activity involves the study of a new class of compounds, MOFs, as electrode materials for NIB batteries. MOFs are crystalline polymers in which aggregates of transition metals (or metal derivatives) are interconnected by organic linker molecules. Depending on the organic molecules used aslinkers, the structure of MOFs can be adjusted in terms of flexibility, porosity and surface area, facilitating the intercalation of molecules larger than lithium molecules.

The latest activity on electrochemical Sss concerns testing procedures and tests on battery modules and cells already on the market, useful for estimating the state of health (SOH) and aging trend of batteries. A test procedure was designed with the intention that it would be adaptable to different SSs in both size and characteristics. In addition,a post mortemanalysis of the cells under test was initiated in order to check the condition of the materials at end-of-life conditions.

The work on large-scale storage was also technology-oriented In particular, safety issues related to the industrial process of extracting and storing natural gas in deep depleted reservoirs were studied through numerical simulations, using the Integrated Geo-Modeling Analysis System (Geo-SIAM), a simulation tool implemented at RSE. In detail, a real storage reservoir located in Lombardy was geologically investigated: a 3D static geologic model of the investigated area and a subsequent 3D fluid dynamic model were created to simulate the operational processes of production and storage of 1 and 12 thermal operating seasons. A geo-mechanical module was also developed to study the effects on rock layers of the pressures involved. The ultimate goal is to determine whether overpressure operation (relative to reservoir discovery pressure) is possible, which would allow for increased storage capacities.