From PV waste to battery anodes: a roadmap for upcycling silicon via battery-grade purification and carbon-source engineering

Abstract

End-of-life (EoL) photovoltaic (PV) modules are generating a rapidly expanding reservoir of silicon that could be upcycled into lithium-ion battery anodes. This review advocates for and delineates a high-value upcycling pathway, transforming EoL photovoltaic silicon into high-performance silicon–carbon (Si–C) anodes for lithium-ion batteries. Adopting a materials-to-electrode perspective, we first establish that the key to this transformation lies in defining and achieving “battery-grade” quality for the recovered silicon. We synthesize specific benchmarks from PV-derived feedstocks (modules, diamond-wire sawing slurry, deposition wastes), including suppression of metallic impurities (Fe, Ni) to near-background levels, early removal of refractory TiO₂, controlled surface oxide, reproducible particle size/surface area, and explicit reporting of dopant type. These benchmarks are directly linked to purification strategies (e.g., HF-free leaching, “acid-first, milling-later” sequences) and inform the selection of four scalable Si–C architectures: conformal core–shell Si@C, carbon-matrix composites, porous Si–C hybrids, and mechanically alloyed composites. We identify carbon-source engineering—encompassing graphitic carbons, hard/soft carbons, nanoscale networks (CNTs, graphene), and polymer-derived functional carbons—as the key design lever controlling electronic conductivity, mechanical stress buffering, SEI stability, and rate performance. In doing so, we incorporate mechanistic insights into impurity/dopant effects into practical guidelines. Further, we synthesize life-cycle and techno-economic analyses into viable process flowsheets that balance silicon purity, co-metal recovery, and sustainability. Concluding the review, we provide a foresighted roadmap connecting the state of EoL PV silicon to purification choices and carbon engineering to reconcile performance, cost, and circular economy aspirations for upcycled PV-silicon-derived Si–C anodes.