Thermodynamically Driven Phase Separation for Wearable Ionic Thermoelectrics

Abstract The integration of high thermoelectric performance, mechanical compliance, and self‐healing capability in ionic conductors remains a fundamental challenge for wearable energy technologies. Here, these limitations are overcome through the thermodynamic design of phase‐separated ionic gels. By precisely modulating the interactions between the in situ polymerizable hydrophilic matrix (PDAC) (Poly([2‐(Acryloyloxy)ethyl]dimethylammonium chloride)) and the hydrophobic ionic liquid (EMIM:TFSI) (1‐ethyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide), spontaneous formation of bicontinuous microstructures is achieved that simultaneously deliver record‐high thermopower (30.80 mV K −1 ), exceptional mechanical properties (762% strain, 2862.51 kJ m −3 toughness), and self‐healing efficiency (85% thermal voltage retention). The microstructure emerges from balanced enthalpic‐entropic contributions as predicted by Flory‐Huggins theory, creating percolated ion‐selective transport channels within a deformable polymer skeleton while maintaining interfacial stability. This approach overcomes the long‐standing trade‐offs among ionic thermophoresis, mechanical robustness, and reparability in conventional ionic thermoelectrics. As a demonstration, 3D‐printed stretchable thermoelectric wristbands with outstanding energy‐harvesting performance are fabricated. The work establishes a paradigm for multifunctional ionic materials, with immediate applications in wearable thermal energy harvesting and adaptive sensors, while providing a framework for next‐generation soft electronics.