Molecular Design and Recycling of Advanced Materials for a Circular Economy: Polymers, Thermoset Composites and Lithium-Ion Battery Cathodes

Background: Plastics, fibre-reinforced thermoset composites and lithium-ion battery cathodes underpin decarbonisation and modern manufacturing, yet most were designed for performance rather than recovery. Plastic recycling rates remain low, composite waste is accumulating and battery-metal demand is outpacing secondary supply. Molecular design for recyclability has become a central research agenda, but its evidence base is fragmented across chemistry, catalysis, biotechnology, electrochemistry and sustainability assessment. Purpose and Scope: This critical narrative review examines whether molecular design and emerging recycling technologies can deliver measurable circularity and environmental benefit across three material classes: thermoplastics, crosslinked thermosets and their composites, and lithium-ion battery cathode materials. It also evaluates how system-level assessment, chemical safety and regulation condition those benefits. Approach: Literature was identified through multidisciplinary and topic-specific scholarly indexes, institutional sources and citation searching, and was appraised qualitatively for waste-stream realism, closure of the material loop, scale, transparency of assessment assumptions and independent replication. Principal Findings: Molecular strategies such as low-ceiling-temperature monomers, embedded cleavable linkages, dynamic covalent networks and defect-targeted relithiation of cathodes are mechanistically well supported and can restore material properties after recovery. Evidence for their performance in contaminated, mixed and ageing waste streams is much weaker, and multi-cycle durability data are scarce. Life-cycle and techno-economic studies often disagree because they differ in system boundaries, displaced products, energy mixes and assumed scale. Mechanical recycling remains economically and environmentally competitive where material quality can be maintained, whereas pyrolysis-based routes and enzymatic recycling of poly(ethylene terephthalate) have not yet shown consistent environmental advantages over virgin production, and most catalytic upcycling routes lack comparable assessment. Direct cathode recycling appears environmentally promising but depends on chemistry-specific collection, sorting and design for disassembly. Implications: Recyclability is a system property that molecular design can enable but cannot guarantee. Progress requires standardised benchmarking on real waste, prospective assessment coupled to design decisions, integration of chemical-safety criteria and infrastructure-aware deployment. The available evidence supports cautious optimism about specific design–recycling pairings rather than general claims of circularity.