Biodegradable Polyester Separator With Ion‐Dipole Interaction for Modulating Interfacial Li‐Ion Flux in Lithium Metal Batteries

Lithium metal batteries (LMBs) are regarded as promising next‐generation energy storage systems owing to their ultrahigh theoretical energy density. However, conventional polyolefin separators suffer from poor electrolyte wettability and limited capability to regulate ion transport, leading to uncontrolled dendritic growth and unstable solid electrolyte interphases (SEIs) that severely compromise battery safety and cycling stability. Herein, a biodegradable polybutylene succinate@polylactic acid (PBS@PLA) composite separator is developed to synergistically regulate Li‐ion transport and enhance interfacial stability. The PBS domains facilitate efficient electrolyte uptake and enhance ionic conductivity, while the highly polar PLA domains modulate Li‐ion distribution through ion–dipole interactions. This cooperative ion‐regulation architecture accelerates charge‐transfer kinetics and promotes the formation of a dense LiF‐rich SEI. Leveraging these advantages, the PBS@PLA separator enables an ionic conductivity of 2.1 mS cm −1 in the regular 1 M carbonate electrolyte and sustains stable Li plating/stripping at a high current density of 10 mA cm −2 . The Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 full cells also retain 80.2% of their initial capacity after 300 cycles at 5C. Moreover, the intrinsic biodegradability of the PBS@PLA separator enables controllable end‐of‐life degradation, facilitating material recycling. This work establishes a viable separator‐engineering strategy that integrates high performance with eco‐friendly recyclability for LMB technologies.