From Waste to Resource: 25 Years Transforming Battery Recycling at IME RWTH Aachen University

Over the past 25 years, battery recycling has evolved significantly in response to evolving German and European legislation, which has progressively raised collection and recycling targets. These regulatory drivers have promoted research into efficient, environmentally benign, and cost-effective processes. Battery recycling has primarily built upon the established pillars of electronic waste processing: pyrometallurgy and hydrometallurgy. Direct smelting of batteries was quickly adopted industrially due to its compatibility with existing facilities for other metallic wastes, despite high energy costs. In contrast, direct hydrometallurgical routes offer high metal recovery efficiencies and lower operational costs but raise concerns regarding wastewater management. A promising third approach, thermal preconditioning at temperatures up to 600 °C, has emerged, enabling the removal of toxic electrolytes and the chemical reduction of complex cathode materials, thereby facilitating subsequent leaching. Each process chain presents distinct advantages and limitations, influenced by factors such as national regulations, battery chemistry, and target products. This review reflects on 25 years of research at IME, RWTH Aachen University, tracing the development of pyrometallurgical, hydrometallurgical, and hybrid routes, with particular emphasis on thermal preconditioning and early-stage lithium recovery (ESLR) as key enablers of higher lithium yields and alignment with future European Union (EU) recycling targets.