The analysis of the aging mechanisms of electrochemical accumulators is one of the most important topics of research activity in this sector. The final goal of the research is to obtain a general increase in the performance of electrochemical storage systems, achievable, in the short term, through an optimal management of the systems using predictive aging models and, in the long term, through an improvement of cell materials. The achievement of these objectives generally requires very different approaches and methodologies.

The research activity conducted in RSE aims to address the issue of aging analysis of storage systems from the broadest possible point of view. For this purpose, an aging analysis methodology that integrates different approaches and aims to pursue the aforementioned objectives has been developed. The methodology is based on performing parallel, rather than sequential, non-destructive aging tests and destructive post-mortem analyses on batteries with the same technology, but different size.

The document reports the preliminary results of non-destructive aging tests carried out on commercial NMC pouch-type lithium-ion cells. The cells tested were subjected to over 1000 equivalent work cycles and 6 months of calendar aging tests, under operating conditions characterized by different stress factors. The results of the aging tests were used to identify the parameters of a semi-empirical aging model for this technology, capable of obtaining a prediction of the battery operating life even under working conditions characterized by the simultaneous presence of different stress factors. The semi-empirical approach combines experimental observations and theoretical analyses and, compared to an exclusively empirical approach, allows a more accurate estimate of the useful life even when the battery is working under operating conditions other than experimental ones. Aging tests were also carried out on modules made with the same type of cells, with the aim of validating the developed aging model. The document reports the Entity-Relationship model of the database in which the results of the aging tests will be entered and which will be built and populated as the activity continues.

In parallel, the post-mortem analysis procedure of the cell materials has started. The document describes the first steps of the procedure, namely the opening of one of the cells, the extraction of samples of the different materials and the assembly of three-electrode Swagelok half-cells starting from the recovered materials. The half-cells will be subjected to electrochemical characterization and aging tests.

Preliminary results of tests for the measurement of electrochemical impedance by spectroscopy performed on cells subjected to non-destructive tests are reported. The purpose of these tests is to identify further diagnostic parameters in addition to those already used.

To continue with the activity, the developed aging model shall be implemented in an algorithm that will allow to predict the operational life of the storage system based on the working conditions and the current state of health.