Second-life applications for retired electric vehicle batteries: Challenges, opportunities, and future directions

The global expansion of e-mobility, driven mainly by the rapid adoption of Electric Vehicles (EVs), is creating an unprecedented increase in the number of retired EV batteries that no longer meet the requirements of automotive performance. This emerging scenario highlights the urgent demand for innovative, sustainable, and scalable management strategies that address environmental and logistical challenges. This review paper provides a state-of-the-art, comprehensive framework that addresses the technical, environmental, economic, and policy aspects of Second-Life Battery (SLB) deployment. Beyond reviewing existing practices, this paper critically assesses the underlying degradation processes that influence SLB performance, the diagnostic and modeling challenges that constrain reliability, and the technical gaps in the repurposing process. Emerging advances in AI-driven prognostics and adaptive management strategies are reviewed for their potential to mitigate heterogeneity, ensure safety, and prolong the application lifetime in stationary energy storage applications of SLBs. Life-cycle assessments across various practices have demonstrated that repurposing offers a more substantial approach compared to traditional direct recycling in reducing carbon footprint; however, economic viability remains dominantly dependent on degradation dynamics, logistics, and regional market conditions. Persistent discrepancies in current regulatory frameworks underscore the need for globally harmonized standards to support large-scale SLB commercialization.