Handling multifunctionality in the life cycle assessment of electric vehicle batteries in a circular economy

Lithium-ion batteries are crucial for the energy and mobility transition but rely on strategic raw materials with rapidly increasing global demand. To reduce dependence on international supply chains and promote sustainability, the EU has introduced regulations such as the EU Batteries Regulation and the Critical Raw Materials Act, which set ambitious circular economy targets and require standardised carbon footprint assessments. However, a widely accepted life cycle assessment (LCA) method is still missing. A key part of this harmonised method is the handling of multifunctionality, as in complex systems like electric vehicle (EV) batteries, various multifunctionalities exist: Many primary battery materials originate from co-production processes, making it challenging to assign environmental impacts to a single material. In battery manufacturing, multifunctionality arises from recyclable waste, particularly from cells and electrodes. During use, batteries can serve parallel (e.g., EV use and vehicle-to-grid) or consecutive functions (e.g., stationary storage after EV use), substituting dedicated storage systems. The recycling at the end of life serves both as waste treatment and as co-production of secondary materials. A standardised LCA approach is not only essential for regulatory reporting but also for internal engineering and development processes to ensure reliable, comparable results and support design decisions. This thesis develops a method to address multifunctionality in the EV battery life cycle, aiming to improve consistency, transparency, and applicability across both policy and engineering contexts. This thesis comprises six research articles focused on the multifunctionality of EV batteries in a circular economy. Article 1 reviews current research and guidelines, emphasising the need for greater harmonisation of the handling of multifunctionality and debating whether universal or case-specific approaches are more suitable. Article 2 analyses multifunctionality in battery cell production, specifically solving the multifunctionality with the typical hierarchy or EoL allocation, and examines the environmental and practical implications of each approach. Article 3 looks at how multifunctionality is handled in gate-to-gate LCA studies of recycling processes, proposing two approaches: a process-focused method using system expansion and a material-focused method using allocation, each with distinct advantages. Article 4 expands the focus to cradle-to-grave LCAs, identifying key stakeholder perspectives and using these to build LCA archetypes that demonstrate how different interests shape LCA outcomes and the importance of consistent end-of-life practices. Article 5 explores inconsistencies in current LCA guidelines across industries and battery raw material applications, revealing disparities that can lead to misestimated system-level impacts and advocating for standardised practices and consistency checks for enhanced transparency. Finally, Article 6 presents a decision tree for LCA practitioners to navigate multifunctionality throughout the EV battery life cycle, incorporating consistency checks and reporting guidance to enhance reproducibility and clarity.