Simultaneously Achieving High Energy Density, Mechanical Robustness, and Closed‑Loop Recyclability in Phase Change Materials for Advanced Thermal Energy Systems

ABSTRACT Solid‐solid phase change materials (SSPCMs) hold great promise for thermal management, yet their development has long been hindered by the “impossible triangle”: simultaneously achieving high energy density, robust mechanical properties, and full recyclability. This study presents a strategy to address this trilemma by constructing a reversible physically crosslinked network based on stereocomplex poly(lactic acid) (sc‐PLA) crystallites. In this system, polyethylene glycol (PEG) segments provide thermal energy storage, while sc‐PLA crystallites stabilized by dense hydrogen bonding serve as physical crosslinkers to impart mechanical integrity. The resulting material exhibits ultrahigh stretchability (1427.7%), remarkable tensile strength (30.1 MPa), high latent heat (122.4 J g − 1 ), and outstanding shape stability. Importantly, the reversible network enables closed‐loop recyclability via hot pressing or solvent processing without compromising performance. Moreover, the physically crosslinked network enables SSPCMs to completely disintegrate in soil within 60 days. By integrating carbon nanotubes (CNT), the potential of our SSPCMs for solar‐thermal‐electric energy conversion is also demonstrated. This work provides a scalable and sustainable pathway to overcome the performance bottlenecks of SSPCMs, paving the way for advanced thermal management materials that integrate mechanical robustness, energy efficiency, and green circularity.