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Report RSE 17001205

Na-beta battery: realization of samples of solid electrolyte with differ composition and develop of a planar mono cell

Functional charge and discharge tests on a planar geometry monocell, definition of the optimal cell configuration and study of new compositions for the ionic conductor membrane ß "-alumina.

The main purpose of the activity is to improve the power density of a sodium beta battery, through the realization of a new configuration of the mono cell. In addition, a new solid electrolyte has been studied and developed.

The sodium beta battery has already reached the commercial application for backup, mobility and time shift purposes, but it can play further, important roles in the electrical energy transmission and distribution control, for voltage regulation and or primary, secondary, tertiary frequency control; in general, for the improvement of power quality. For this type of applications, the storage system must be characterized by rapid response and high performance in terms of power.

This type of battery has high specific energy, but it has to improve specific power. In particular it uses a ceramic material, as the ion transport membrane between the two anodic and cathode compartments. It is referred to as sodium β"-alumina, which is able to perform the function of ionic conductor at high temperatures, reaching maximum efficiency in the operating condition at about 300° C. Currently batteries, denominated sodium beta, are produced with a "cup" geometry of the β"-alumina membrane; this configuration allows the containment of the reagents, but it does not allow to optimize the specific power of the cell. The study has thus focused on the possibility to realize a mono cell with a planar geometric configuration of the ceramic membrane of β "-alumina: this new design must be able to "contain" the reagents, which are present in liquid form and are chemically very aggressive, especially sodium, at the operating temperature; that means to study a new sealing between β”-alumina and the metallic case of the cell. In addition, we also tested new ionic electrolyte formulations, with the intention of making a conductive ion membrane with better properties, which can contribute to power density increase.

The activity has allowed to perform the first functional tests on a single planar cell, that was built according to the technological solutions, developed and tested in the previous three years, and employing both electrolyte and cathode reagents used industrially. The experiments carried out on single planar cell, through a process of charging and discharging cycles, have validated the new sealing system of the geometric configuration, but they also identified some critical points of the experimental set up adopted.

At the same time, the experimental activity has regarded two new formulations of b"alumina: the former doped with potassium and the latter with zirconium oxide. The chemical and physical properties of the new formulations were characterized as function of the quantity of the dopants.

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