Electric vehicle (EV) batteries, i.e., currently almost exclusively lithium-ion batteries, are removed from the vehicle once they no longer meet certain requirements. However, instead of being disposed of or recycled, the removed batteries can be used in another, less demanding application, giving them a “second life”. Research in the field of second-life batteries (SLBs) is still at an early stage and, to better understand the “second life” concept and the related challenges, potential second-life applications need to be identified first. Using a detailed study of the scientific literature and an interview with field experts, a list of potential second-life applications was drafted. Afterwards, a technical, economic, and legal evaluation was conducted to identify the most promising options. The findings of this research consisted of the identification of 65 different mobile, semi-stationary and stationary second-life applications; the applications selected as most promising are automated guided vehicles (AGVs) and industrial energy storage systems (ESSs) with renewable firming purposes. This research confirms the great potential of SLBs indicating that second-life applications are many and belong to a broad spectrum of different sectors. The applications identified as most promising are particularly attractive for the second-life use of batteries as they belong to fast-growing markets.

Upon reaching certain limits, electric vehicle batteries are replaced and may find a second life in various applications. However, the state of such batteries in terms of aging and safety remains uncertain when they enter the second-life market. The aging mechanisms within these batteries involve a combination of processes, impacting their safety and performance. Presently, direct health indicators (HIs) like state of health (SOH) and internal resistance increase are utilized to assess battery aging, but they do not always provide accurate indications of the battery’s health state. This study focuses on analyzing various HIs obtained through a basic charging–discharging cycle and assessing their sensitivity to aging. Commercial 50 Ah pouch cells with different aging histories were tested, and the HIs were evaluated. Thirteen HIs out of 31 proved to be highly aging-sensitive, and thus good indicators. Namely, SOH upon charging and discharging, Coulombic efficiency, constant current discharge time, voltage relaxation profile trend, voltage–charge area upon discharging, hysteresis open circuit voltage HIs, and temperature difference between the tabs upon charging. The findings offer valuable insights for developing robust qualification algorithms and reliable battery health monitoring systems for second-life batteries, ensuring safe and efficient battery operation in diverse second-life applications.

This perspective provides a multidisciplinary assessment of the use of lithium-ion batteries from electric vehicles (EVs) for second-life applications, motivated by the need to improve resource efficiency, reduce environmental impacts, and support a circular battery economy. Second-life deployment requires the integrated consideration of technical performance, legal compliance, and economic viability. The analysis combines a technical evaluation of battery aging mechanisms, operational load effects, and qualification strategies with a legal assessment of the EU Batteries Regulation (EU) 2023/1542 and an economic analysis of market potential and business models (BM). From a technical perspective, the limitations of State of Health (SOH) as a standalone indicator are demonstrated, highlighting the need for multiple health indicators and degradation-aware qualification. A scalable two-step qualification approach, combining qualitative inspection with a standardized quantitative measurement protocol, is discussed. From a legal perspective, regulatory requirements and barriers related to repurposing, waste classification, and conformity assessment are analyzed. From an economic perspective, business model patterns and market dynamics are evaluated, identifying Automated Guided Vehicles (AGVs) and industrial Energy Storage Systems (ESSs) for renewable firming as particularly promising applications. The paper concludes with recommendations for action and key research needs to enable safe, economically viable, and legally compliant second-life deployment.