A Review: Mechanisms, Processes and Design Principles of Recycling Spent Lithium-Ion Battery and Biomass.

End-of-life lithium-ion batteries (LIBs) and biomass wastes are usually studied in separate fields. This review shows that they should also be understood as complementary reaction systems. Biomass not only acts as a cheap carbon source but also provides reductive gases, biochar, organic acids, ligands, and redox-active organics to enable LIB recycling. Spent LIB-derived materials can serve as both a valuable resource and a catalyst to leverage biomass conversion. On this basis, this Review brings together three directions that are discussed in one framework: biomass-assisted thermochemical recycling, biomass-derived leaching systems, and LIB-enabled catalytic biomass valorization. This review identifies the common principles that control these processes, including oxygen potential, phase evolution, kinetics, coupled acid-redox-coordination chemistry, and catalyst design. We further compare process configurations, product pathways, and environmental trade-offs. Future work should focus on resolving coupled reaction mechanisms, defining composition and reactor design windows, integrating process-level assessment, and enabling data-driven optimization for scalable and low-impact corecycling systems.