Active Separators Featuring PF 6 − Anion‐Regulating Interface for Long‐Term Stable Li‐Based Batteries

ABSTRACT Developing high‐energy lithium batteries inevitably involves separators that suppress uncontrolled ion transport and parasitic reactions over repeated cycling. Here, we introduce a dual‐functional active separator comprising a uniformly dip‐coated double‐bond‐containing poly(vinylidene fluoride) (DPVDF) layer with covalently cross‐linked branched polyethyleneimine (BPEI) robust framework interfaces. The amine‐enriched DPVDF–BPEI‐modified separator (PDB) electrostatically regulates PF 6 − anions, as evidenced by spectroscopic, computational, and electrochemical studies. PF 6 − regulation suppresses significantly hydrofluoric acid (HF)‐forming fragmentation and facilitates selective Li + diffusion, leading to ca. twice higher Li + transference numbers (polypropylene (PP): 0.49 and PDB: 0.80) and ca. 3 times higher Li + diffusion coefficient (PP: 0.46 × 10 −6 and PDB: 1.29 × 10 −6 cm 2 s −1 ) than PP. In addition, it thereby results in the formation of ultrathin, compositionally uniform electrode–electrolyte interphases (SEI/CEI). Those unique effects of the PDB enable long‐term stability, ca. 1,000 cycles in Li||LFP and ca. 400 cycles in Li||NCM811 half‐cells. The Si||LFP full‐cell exhibits stable cycling for more than 400 cycles at 3.0 C. The PDB supports dendrite‐free operation for 1,000 h in Li||Li symmetric cells, demonstrating uniform Li deposition. This work establishes a scalable separator design strategy that integrates structural durability with targeted anion regulation and efficient ion‐diffusion control, providing a practical pathway toward stable, high‐energy lithium‐based batteries.