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Report RSE 18002401

Na-beta Battery: realization of the solid electrolytes with new composition anddevelopment of a planar monocell

The activity carried out concerns on one hand the development of a new planar mono-cell configuration for the battery called nickel sodium chloride and on the other the development of a new solid electrolyte (¿ "alumina) with the SPS technique defects free.

The current activities are focused on two topics: the first one is to configure a prototype of anelectrochemical mono cell for a sodium beta battery with planar geometry; the second one concerns thestudy and development of new formulations for solid electrolytes.

The sodium beta battery can play an important role in support of the electrical energy transmission anddistribution, intervening for example in conditions of voltage and frequency instability and, in general,for the improvement of power quality. For this type of applications, the storage system must becharacterized by fast time response and high performance in power.

This type of battery has high specific energy, but it needs to improve specific power. In particular, thebattery uses a ceramic material as ion transport membrane between the anodic and cathodiccompartments, named sodium β"-alumina, which is able to perform as ionic conductor at hightemperatures, reaching best efficiency in the operating condition at about 300°C. Currently batteries,called sodium beta, are produced with a “cup” geometry of β"-alumina; this configuration can containthe reactant inside, but does not allow to optimize the specific power of the cell. The studies have thusbeen focused on the possibility to realize a mono cell with geometric configuration of the β"-aluminamembrane in planar shape, which must also be able to "contain" the reagents. At the operatingtemperature, reagents are in liquid form and are chemically very aggressive, especially sodium.

In addition, new formulas for ionic electrolyte have been tested, with the purpose of improving ionicconductivity.

The planar configuration would in fact allow to obtain batteries not only characterized by high energydensities, but exhibiting also a higher power density. Moreover, the planar geometry would allow tostack the single monocells, making the battery more compact and improving thermal control.Furthermore, during this year the activities aimed at developing solid electrolytes with conductive ionicproperties better than the state of the art have continued.

On the basis of the results obtained during the previous years, a new single cell has been designed, builtand assembled to overcome the problems encountered in the past. Subsequently, charge and dischargetests have been started, using industrial grade solid electrolyte and cathodic reagents. Thisexperimentation confirmed the validity of the adopted geometry and of the technological solutionsdeveloped, although some critical issues have been identified that require further studies to be carriedout in collaboration with the national manufacturer of this type of battery.

As concerns the development of a new solid electrolyte, the experimental activity has been focused onthe identification of the possible causes that lead to the formation of microscopic defects and cracksresponsible for the poor mechanical properties and ionic conductivity of the β” alumina samples realizedby means of the SPS technique, although they have a degree of purity higher than 90% and a densitybetween 92 and 98% of the theoretical value. The tests have therefore aimed at verifying the effect ofthe sintering process parameters (i.e. temperature and pressure). At the same time, sintering tests in aoven were carried out to evaluate the effect of the addition of binders to the powders in order to improvethe degree of densification of the samples.

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