*3.2. System Boundaries*

In the LCA methodology, the system boundaries definition is a way to identify which processes within the entire life cycle of the involved systems need to be analyzed or, for the sake of simplification, can be neglected. The system should be modelled to have only input and output elementary flows. System boundaries define process phases that need to be included within the LCA and their choice has to be consistent with the target of the study. Except for [8,13,19], which do not define clearly the system boundaries of their work, all the other documents explain their LCAs system boundaries in a clear way. Eight studies out of seventeen [7,9,11,14,16–18,20] analyze all batteries phases (cradle to grave): raw materials extraction and manufacturing, batteries production, transportation, use phase, end of life with material recycling. Three studies [10,12,22] analyze only batteries production, by a cradle to gate assessment, due to the lack of reliable information for modelling the use and the end of life phases. In reference [21], system boundaries include the production and the use phases, not considering the end of life impacts. Whenever possible, as suggested in references [15] and [4], we recommend to go through cradle to grave analysis, considering all phases of a battery during its life cycle.
