Extending battery lifecycles: A holistic review of second-life lithium-ion technology in sustainable energy systems from assessment to emerging trends

The increasing global focus on sustainability and low-emission transportation has driven the expansion of electric vehicles (EVs), resulting in a significant rise in lithium-ion battery production. When a battery’s capacity declines to around 70–80% of its original value, it can no longer meet the necessary performance standards for EVs and is subsequently discarded. Although these batteries retain considerable residual energy and material value, they are well-suited for second-life applications in less demanding stationary contexts. Repurposing decommissioned EV batteries as energy storage systems extend their service life, reduce lifecycle costs, and support the circular economy by minimizing waste and resource extraction. This review provides a comprehensive evaluation of recent developments in second-life battery (SLB) research, including degradation processes, assessment and repurposing methods, and testing systems. This review examines various methods for estimating state-of-health and remaining useful life, with a focus on the increasing application of artificial intelligence (AI) to improve prediction accuracy and operational efficiency. The study discusses the latest developments in specialized battery management systems designed for SLBs, ensuring safety, reliability, and performance. Furthermore, the discussion encompasses recycling and upcycling processes concerning material recovery and the sustainability of value creation. The discussion includes published datasets and their limitations to inform future AI-centric development. Although the potential of second-life batteries is increasingly recognized, large-scale adoption remains constrained by safety risks and uncertain cost–benefit trade-offs. This review synthesizes repurposing decision pathways and discusses their alignment with sustainable development goals. This study identifies current challenges and outlines future research agendas focused on standardized repurposing procedures, economic and environmental impact assessments, and policy frameworks to promote the scaling up of SLB adoption and integration in renewable terminals.