Upcycling Piezoelectric Single‐Crystal Debris Into High‐Performance Flexible 0–3 Composites

High‐value piezoelectric single‐crystal debris remains an untapped resource for flexible electromechanical materials. Although relaxor‐based ferroelectric single crystals offer exceptional piezoelectric properties, off‐cuts inevitably generated during precision processing are typically discarded because their irregular geometries prevent direct device integration. Here, we report a recycling‐to‐device upcycling strategy that converts industrial Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 (PMN–PT) single‐crystal debris into high‐performance flexible 0–3 piezoelectric composites and energy harvesters through material–structure–mechanics co‐design. A ball‐milling‐based particle refinement procedure converts the debris into dispersible particulate fillers, while dielectrophoresis (DEP)‐assisted curing reorganizes randomly dispersed particles in a polydimethylsiloxane (PDMS) matrix into vertically connected quasi‐1–3‐like networks. The polymer matrix provides mechanical tunability, allowing flexibility and dynamic stress transfer to the aligned single‐crystal network to be jointly optimized. The optimized composite achieves a d 33 of 118.5 pC N −1 while retaining mechanical flexibility, placing it among the highest‐performing flexible 0–3 piezoelectric composites. Comparative experiments and finite‐element simulations reveal that single‐crystal‐derived fillers exhibit stronger DEP‐induced enhancement than polycrystalline counterparts owing to more coherent intraparticle electromechanical conversion. Integrated into flexible energy harvesters, the optimized composite delivers a peak areal power density of 284.2 µW cm − 2 . This work establishes a scalable upcycling pathway for reutilizing high‐value functional crystal waste in flexible self‐powered electromechanical systems.