On the second life of lithium-ion batteries from electric vehicles: characterisation, ageing and applications

The transformation of our energy consumption and production model is increasingly urgent. Environmental, economic and social problems associated with fossil fuels have prompted the government and public reaction in the search for alternative solutions. Thus, the transition in the automotive sector towards an electric fleet is already a reality. Lithium-ion batteries are the core of electric vehicles, as they enable autonomy and operation in a similar way to their combustion counterparts. However, the performance features of these batteries degrade due to usage, in such a way that they are retired when their initial energy capacity fades by 30 %. The reuse of electric vehicle batteries has recently emerged as an alternative that allows benefiting from the remaining energy capacity, thus extending their lifetime. Stationary applications, such as the integration of renewable energies or the provision of grid services, are considered promising scenarios for these second-life batteries. Nevertheless, the technical and economic feasibility of these storage systems is currently uncertain. This thesis focuses on the technical feasibility of second-life lithium-ion batteries from electric vehicles. The study has a significant experimental approach, by using real batteries that have already ended their first life. The main work lines of the thesis are: • Revision of the existing state of the art on second-life batteries. • Characterisation of the internal state and analysis of dispersion. • Study of degradation and durability depending on ageing. • Improvement of the internal state assessment, both in the repurposing stage and during the second-life operation. • Study of the technical feasibility of a repurposed prototype with secondlife modules in different stationary applications.