In Situ Amidation‐Derived Interfacial Modulation for Homogeneous Ultra‐High Nanoparticle Loading Toward Robust and Flexible Piezoelectric Composites

ABSTRACT Hybrid materials‐based composites offer resilient and distinctive properties that can be utilized in a broad range of fields compared to traditional single‐phase materials, especially gaining attention in the field of composite‐based flexible piezoelectric energy harvesters (f‐PEHs). However, dispersing pristine inorganic fillers into an organic matrix presents challenges such as particle aggregation, interfacial incompatibility, and heterogeneous dispersion, which limit the ability to achieve uniform ultra‐high ceramic loading to improve the performance of f‐PEHs. Herein, a polydopamine (PDA) surface coating technology was introduced to BaTiO 3 @BaSrTiO 3 core–shell (CS) piezoelectric nanoparticles to inhibit particle aggregation, interfacial incompatibility, and heterogeneous dispersion inside the polymeric matrix. The in situ polymerization of PDA within the PI matrix creates cooperative covalent and non‐covalent interfacial interactions, enabling homogeneous dispersion and achieving 80 wt.% filler loading. These achievements were theoretically verified by employing a density functional theory calculation. The hybrid composite film with high contents (80 wt.%) of PDA‐coated CS piezoelectric nanoparticles exhibits enhanced microstructural stability and a superior piezoelectric coefficient (d 33, eff ≈ 13.4 pm/V). These features promote an efficient stress transfer, a strong grain‐to‐grain connectivity, and an improved cumulative electric dipole alignment, which results in highly‐efficient energy conversion of energy harvesters. The optimized piezocomposite‐based f‐PEH has a maximum open‐circuit voltage ( V OC ) of ∼5.11 V and a short‐circuit current ( I SC ) of ∼1.12 µA when subjected to repetitive mechanical bending forces. Furthermore, our piezo‐hybrid material technology, realizing the ultra‐high loading of ceramic fillers inside a polymeric matrix, provides the feasibility of robustness under extreme environmental conditions, highlighting suitability for space and nuclear applications.