## 1 Introduction
In the literature, there are many studies concerning the technical and economic aspects of the storage systems, while their environmental issues have only recently begun to be dealt with. In most cases, only the reduction of carbon emissions during the operational life is analyzed, and the positive contribution to the climate change reduction is reported. Nonetheless, for a clearer understanding of their total environmental impact, it is necessary to consider both the production and the disposal phases of these systems, in addition to their regular life cycle. [PERSON] et al. [10] evaluated the CO\({}_{2}\) footprint of four types of battery for different grid applications considering production, installation, and operation, while end-of-life is neglected. The life cycle and the energy density are found to be key factors for CO\({}_{2}\) emissions as well as the carbon intensity of the electricity used in the battery production process. The results highlight that the most lithium-ion (Li-ion) and NaNiCl batteries show good performance, whereas lead-acid batteries exhibit the worst due to their low life and internal efficiency. Conversely, the environmental performance of redox-flow batteries is strongly dependent on the application. This battery technology is deeply analyzed by [PERSON] et al. [11], and the high recyclability of these batteries is emphasized as an advantage for a life-cycle sustainability. Despite that, the weak points are the vanadium pentoxide production and the low efficiency. A review of life-cycle assessment (LCA) studies on Li-ion batteries, with a focus on the battery production process, has been conducted by [PERSON] et al. [12]. In this case, the results show that research efforts should not only be focused on energy density but also on maximizing cycle life, charge-discharge efficiency, and cycle life. A study of a hybrid system on an island consisting of wind and photovoltaic (PV) electricity generation and a large-scale lithium titanate battery in place of a diesel engine is presented in Reference [13]. The authors found that the production of the battery accounts only for 6% of the total environmental impact. It has the highest impact on acidification, caused by SO\({}_{2}\) emissions from nickel production, and on ozone depletion, due to the use of halogenated hydrocarbon as cooling medium. A particular use of batteries is studied in Reference [14], which analyzed the environmental benefits and drawbacks of using repurposed batteries from electric vehicles in second-use applications instead of new batteries. As expected, the results show that the highest environmental benefits refer to impact categories dominated by the manufacturing and repurposing stages, such as abiotic depletion potential and mineral resources. The sustainability of lead-acid, Li-ion, and concentration gradient flow batteries is compared to that of other storage technologies, such as compressed air and pumped hydro energy storage (PHES) systems, by means of a multi-dimensional life-cycle assessment by [PERSON] et al. [15]. The lithium-ion battery system has the lowest exergy losses, impact on human health, and ecosystem diversity, while PHES is the best for human health, ecosystem diversity, resource availability, and global warming potential. In summary, the impact of the building phase is predominant due to the large infrastructure; depending on the technology, it is about 96-100% for human health and ecosystem, about 85-99% for the resource consumption, and 91-99% for global warming potential (GWP). The highest values refer to Li-ion batteries and the lowest to the blue battery system, which is a concentration gradient flow battery. Interesting results for the environmental assessment of other storage technologies are reported and discussed in a study performed by [PERSON] et al. [16]. The focus is on a compressed air energy storage (CAES) system connected with a windfarm.