Self-powered rehabilitation monitoring via cation-regulated interfacial polarization in fluoride-filled P(VDF-TrFE) sensors

Flexible piezoelectric sensors hold immense promise for wearable bioelectronics. Nevertheless, the inherently high polarization energy barrier of poly (vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) increases the energy requirements of the polarization process and limits further improvements in polarization efficiency and device performance. Herein, a cation-regulated interfacial polarization enhancement strategy via filled inorganic fluorides (AlF 3 , BaF 2 , CaF 2 , and MgF 2 , respectively) with unique fluoroaffinity effect, is proposed to fundamentally boost the piezoelectric and electromechanical performance of P(VDF-TrFE). First-principal calculations and spectroscopic analyses reveal a synergistic dual-interfacial network comprising - C - H···F hydrogen bonds and cation-driven ion-dipole interactions. Notably, the high-valence Al 3+ maximizes interfacial charge transfer, establishing a robust built-in electric field in the P(VDF-TrFE)/AlF 3 composites. This significantly lowers the conformational transition barrier, driving a massive electroactive β -phase transition (~ 89.0%) and facilitating ferroelectric domain switching with a substantially reduced coercive field. Consequently, the optimized AlF 3 -filled film delivers an outstanding piezoelectric strain coefficient (| d ₃₃|≈ 37.5 pC/N) in quasi-static mode, and achieves an exceptionally durable peak power density of 85 µW cm − 2 in as-assembled flexible sensor. This enables continuous self-powered kinematic monitoring, accurately capturing the multi-scale range of motion in human joints, thereby providing an atomic-level design paradigm for next-generation digital medical rehabilitation. Graphical abstract