Recycling of spent LiFePO4 extraction slag: Current status and future prospects

Recovering LiFePO4 extraction slag (LES)—the FePO4‐rich residue formed after Li leaching from spent LiFePO4—has become pivotal to minimizing resource losses, mitigating environmental risks, and advancing circularity in lithium-ion battery value chains. However, integrative frameworks that link closed-loop routes (returning to battery precursors/cathodes) with non-closed-loop upcycling are still limited, constraining process optimization and scale-up. This review synthesizes current progress in LES recycling with emphasis on maximizing recovery efficiency and product value. In closed-loop pathways, hydrometallurgical purification removes impurities to yield battery-grade FePO4 as an LiFePO4 precursor, while direct relithiation (e.g., solid-state sintering aided by Li sources and reductants) restores Li and reduces Fe3+ to Fe2+, thereby regenerating LiFePO4 cathodes from LES. In non-closed-loop pathways, compositionally guided upcycling converts LES into advanced materials (e.g., high-performance electrodes, high-capacity adsorbents), thereby broadening the techno-economic value propositions. We also distill lessons from early industrial practice, identifying constraints arising from feedstock variability, energy-cost coupling (thermal/chemical utilities), and product-quality assurance (battery-grade specifications). Finally, we map research directions—including data-driven feed characterization and process control, defect-healing relithiation strategies and interfacial engineering, quality grading and market pathways, and multi-scenario deployment—to enhance the technical and economic sustainability of LES recycling and accelerate its contribution to a circular battery economy.