Inorganic-Directed Charge Delocalization Channels: Boosting Uniform Charge Distribution and Rapid Na⁺ Transport for Solid-State Sodium Metal Batteries

Abstract

Composite polymer electrolytes (CPEs) are promising for all-solid-state sodium metal batteries but suffer from low ionic conductivity, which stems from limited Na-salt dissociation and narrow polymer amorphous domains, as well as sluggish ion transport caused by discontinuous composite interfacial charge-transfer paths, and poor electrode/electrolyte interfacial stability. This study proposes an original molecular interface engineering strategy: inorganic Zr⁴⁺ induces organic phase reconstruction to build continuous high-speed ion channels, simultaneously accelerating Na-salt dissociation and reducing ion migration energy barriers. Zr⁴⁺ directs the oriented reorganization of polar groups (─C≡N) to alleviate Na-metal anode interfacial passivation, facilitate NaF/Na₃N-rich stable solid electrolyte interphase formation, and enable uniform Na deposition. Moreover, Zr─N═C metal-ligand coordination at the organic/inorganic interface induces interfacial electronic coupling and charge redistribution, promoting fast Na⁺ migration along continuous coordination pathways. The developed CPEs, denoted as polyacrylonitrile-metal organic framework@polyethylene oxide-Na[N(SO₂CF₃)₂] (PM@PN), show a synergistic interface-bulk effect that significantly enhances electrolyte performance, as evidenced by a reduced apparent activation energy of 0.027 eV (derived from Vogel–Tammann–Fulcher, VTF fitting above T_m), an enhanced ionic conductivity of 3.52 × 10⁻⁴ S cm⁻¹, and a Na⁺ transference number of 0.67 at 60°C, along with an expanded electrochemical window of 5.06 V. The Na|PM@PN|Na symmetric cell demonstrates 0.56 mA cm⁻² critical current density and stable Na deposition/stripping over 700 h at 0.4 mA cm⁻². Additionally, the assembled Na₃V₂(PO₄)₃|PM@PN|Na full cell maintains 93.99% capacity retention after 200 cycles at 0.1 C, confirming PM@PN's applicability in advanced all-solid-state sodium metal batteries.

Keywords

interface reconstruction / ion transport highways / composite polymer electrolyte / all-solid-state sodium metal batteries

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