Internal Electric Field‐Guided, Low‐Adsorption Ferroelectric Anode Protective Layers for Sustainable Suppression of Polysulfide Side Reactions in Lithium–Sulfur Batteries

Abstract

Lithium–sulfur batteries (LSBs) offer energy densities beyond lithium‐ion batteries, yet parasitic reactions between soluble polysulfides and lithium metal cause active‐sulfur loss and porous Li, undermining cycle life. To address this problem, an anode protective layer is needed, but interactions between protective layers and polysulfides remain insufficiently understood. In this work, representative anionic and ceramic protective layers are employed as model systems to establish how strong polysulfide adsorption and persistent sulfur‐species retention affect protective‐layer functionality. Building on these findings, a positively polarized ferroelectric β‐pvdf layer incorporating fluorinated boron nitride nanosheets (PPFBN) is introduced. Corona poling aligns polarization to establish an internal field, while insulating nanosheets suppress free‐charge relaxation, thereby sustaining the field. The field promotes Li + transport to the anode and impedes the approach of polysulfide anions, while intrinsically low polysulfide affinity limits long‐term degradation of layer functionality. With PPFBN, Li/Li symmetric cells cycle stably for >1000 h in polysulfide‐containing electrolytes at 2 mA cm − 2 and 2 mAh cm − 2 . Full cells retain 80.4% capacity after 500 cycles at 0.5 C; under lean‐electrolyte conditions, cycle life extends by more than 150 cycles relative to bare Li. This study establishes a ferroelectric‐field, low‐polysulfide‐affinity design principle for durable anode protection in LSBs.