The report illustrates the activities and results of the research carried out in the project “Energy storage materials and technologies for the electricity system”, which concerns the development of small-scale electrochemical storage systems (SS), as well as the development of large-scale hydroelectric and natural gas storage. Activities on electrochemical SS will focus on the development of electrode materials and the electrolyte. In particular, we intend to create a single cell of a high temperature (around 300°C) sodium/nickel chloride battery in which the electrodes are liquid metals and the electrolyte is a solid ion conducting ceramic material (β” alumina).

During this implementation plan (PAR), we focused on the creation of a new cell structure to allow the first filling of the electrode materials in a single compartment and “cold”, and on the creation of the β” alumina through a new sintering technique called Spark Plasma Sintering (SPS). Another activity concerns the development of a sodium ion battery (NIB) with an anode based on porous lamellar materials, called MXenes, obtained by chemical treatment (exfoliation) of mixed metal carbides (e.g. Ti-Al, Ti-Si, etc.) belonging to the MAX phase family.

During this PAR, these materials have been prepared and characterized to determine their ability to intercalate sodium ions and to verify that they can be used as anodes in NIB batteries. A final activity on electrochemical SS concerns the study of molten metal batteries using salts in the liquid state as ion transport electrolytes. This technology, borrowed from the electrolysis process used to produce aluminum, does not currently have a product on the market. The three-year objective is to start experimenting with this battery as well.

During this PAR, the advantages and disadvantages of this technology were analyzed by evaluating the potential difference of different pairs of metallic electrodes, also characterized by other parameters such as melting temperature, density (to ensure stratification of the reagents by gravity), toxicity, availability in nature and supply costs. The large-scale storage activity also has a technological orientation. In particular, an innovative hydroelectric storage system using underground pumping in caves has been studied. Essentially, a reservoir (upstream or downstream) consists of an underground cavity hydraulically connected to another surface reservoir.

During this PAR, a study was carried out on the national potential of this technology (with particular reference to a type of spiral cavern created using “mechanical moles”), identifying the most geologically suitable areas for the construction of this type of plant, estimating the construction costs and assessing the macroeconomic viability of the investment. Another large-scale storage activity concerns the storage of natural gas and the safety issues associated with the use of depleted hydrocarbon reservoirs for this purpose. During this PAR, the industrial process of gas storage and delivery in deep reservoirs was studied using numerical simulations.

Specifically, the activities were focused on an area defined as “virtual Sergnano”, located in Lombardy. The area has been the subject of geological investigations, which have been used to create a 3D static geological model of the area under investigation, and subsequently a 3D fluid dynamic model for the numerical simulation of the operational processes for the production and storage of natural gas in geological reservoirs, in order to study the safety problems associated with the pressure variations induced by the operational processes themselves.