Isotropous Sulfurized Polyacrylonitrile Interlayer with Homogeneous Na+Flux Dynamics for Solid‐State Na Metal Batteries

Abstract Inorganic solid‐state electrolyte (SSE) based Na‐metal batteries have received extensive attention in next‐generation lithium‐free energy storage systems with both high‐security and superior electrochemical performance. Herein, in contrast to the conventionally used polymer/ceramic/polymer sandwich electrolyte, an efficient green and scalable powder‐polishing synthetic method is developed to fabricate a pyrolyzed‐polyacrylonitrile modified Na super ionic conductor (NASICON) electrolyte to relieve polarization of integrated composite SSE and ameliorate interfacial contact between the electrolyte and the Na anode. Furthermore, introducing S in the preferable isotropous sulfurized polyacrylonitrile (SPAN) interlayer can trigger dehydrogenation and cyclization of polyacrylonitrile with chemically‐bonded short‐chain SS segments, which can bond with Na + to redistribute the interfacial electric field and homogenize transported Na + flux, leading to transition of Na deposition behavior from dendrite growth mode to lateral flat‐shape growth tendency. The conjugated polymer backbones possess delocalized radicals that can activate formed short‐chain sulfides to reconnect to the backbones, thus maintaining superior structural stability. Benefiting from the rational interfacial design, a record‐high value of 1.4 mA cm −2 for critical current density of Na/SPAN‐NASICON/Na cells is obtained. Moreover, SPAN is used as a cathode to assemble solid‐state Na/SPAN‐NASICON/SPAN Na‐organosulfur batteries, demonstrating superior capacity and cycling‐stability. The rational SPAN‐based structural design strategy may provide an avenue for potential application of solid‐state alkali metal batteries.