A Star Boron-Cored Macromolecule-Mediated Multi-Scale Relaxation Strategy for Overcoming the Conductivity-Robustness Trade-Off in Polymer Electrolytes

Poly(ethylene oxide) (PEO)-based solid electrolytes are pivotal for enabling high-safety and high-energy-density all-solid-state lithium metal batteries (ASSLMBs) yet remain fundamentally constrained by the inherent trade-off between ionic conductivity and mechanical robustness. Herein, we report a supramolecularly expanded polymer electrolyte engineered via a star boron-cored poly(ethylene glycol) (BPEG) macromolecule. The BPEG architecture incorporates a Lewis acidic boron core that promotes salt dissociation through anion-trapping, along with three flexible PEG arms that are intrinsically ion-conductive and structurally homologous to the PEO matrix. Critically, these PEG arms mediate the formation of a dynamic multiscale hydrogen-bond network between the PEO chains. This unique architecture, which disrupts PEO crystallization to unlock segmental motion, operates on a sequential relaxation mechanism: labile weak hydrogen bonds dissociate preferentially to facilitate Li + transport, while robust strong hydrogen bonds persist to maintain mechanical integrity. Such design yields a robust yet adaptive supramolecular network that concurrently establishes continuous ion-conduction pathways and enhances structural robustness. As a result, the SEPE demonstrates high ionic conductivity, improved mechanical strength, and stable interfacial compatibility with lithium metal, enabling highly stable Li plating/stripping and delivering excellent performances in high-loading practical ASSLMBs. This work introduces a feasible multiscale relaxation supramolecular strategy for high-performance polymer electrolytes.