The report presents the activities and results of research aimed at developing small-scale electrochemical storage materials and technologies, as well as large-scale storage functional to the national transmission grid.

Activities in the area of electrochemical storage mainly concern the study, formulation and synthesis of innovative materials, the design and implementation of new cell designs, and physico-chemical, electrochemical and diagnostic testing of cells and batteries.

One activity concerns the development of a planar geometry for a high temperature (about 300°C) single cell sodium/nickel chloride cell in which the electrodes are liquid metals and the electrolyte is a solid ion conducting ceramic material (β-alumina). In particular, new technological solutions have been proposed that can guarantee the tightness of the compartments and improve cell performance (work on the first “cold” charge, capacity and cyclability), as well as a process for sintering β-alumina by spark plasma sintering (SPS), capable of producing artefacts with increased ionic conductivity and strength.

Another activity concerns the development of a sodium ion cell (NIB) with an anode based on porous lamellar materials called MXenes, obtained by chemical treatment (exfoliation) of mixed metal carbides (e.g. Ti-Al) belonging to the MAX-phase family. In particular, the processes of synthesizing the MAX-phases (via SPS), grinding them to reduce them to powder of appropriate particle size, and exfoliating them with appropriate HCl and NaF solutions were refined. The MXenes thus obtained were characterized as anodes in anode half-cells with “button” (coin) geometry, using metallic sodium as counter-electrode, to determine their ability to intercalate sodium ions. A cathode material suitable for combination with MXenes was also produced: work was carried out on optimising a wet synthesis process of mixed oxides of sodium and manganese to produce a specific material (Na_0.44MnO₂) with its own acicular crystal structure capable of intercalating sodium ions. The material was also subjected to electrochemical characterization in cathode half-cells, employing metallic sodium as a counter-electrode.

The last experimental activity on electrochemical type SdAs concerns the test procedures and diagnostic tests on battery modules and cells already on the market, useful for estimating the state of health (SOH) and aging trend of batteries. In particular, work was done on post-mortem analysis of aging cells to verify the condition of the materials. A new method of opening cells with the cells not fully discharged has been implemented to limit material damage due to over-discharge.

The work on large-scale storage also had a technological orientation: 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 (GeoSIAM), a simulation tool implemented at RSE. In particular, a real storage reservoir located in Lombardy was subjected to geological, fluid dynamic, and geo-mechanical modeling investigations: a 3D static geological model of the investigated area and a subsequent 3D fluid dynamic model were created to simulate the operational processes of production and storage. a geo-mechanical module was also developed and integrated into GeoSIAM to study the effects of the pressures at play on the rock layers, including subsidence and heave. The ultimate goal is to determine whether overpressure operation (relative to reservoir discovery pressure) is possible, which would allow for increased storage capacities.