In Situ Hetero-Layered Quasi-Solid-State Electrolyte Enable Enhanced Ion Transport for Safe Sodium Metal Batteries

Abstract

Solid-state sodium metal batteries with high energy density are promising candidates for next-generation energy storage systems. Their bottleneck lies in the solid electrolytes, which must ensure flawless solid-solid contact and electrochemical compatibility with the Na anode and sufficient Na+ conductivity at room temperature. Herein, an in-situ polymerized hetero-layered quasi-solid-state electrolyte, denoted as PANO-SN, was developed by integrating a mechanically reinforced polyacrylonitrile (PAN)/Na3Zr2Si2PO12 (NZSPO) inner framework with in situ polymerized succinonitrile (SN)-based deep-eutectic interfacial layers. the resulting PANO-SN electrolyte achieves an ionic conductivity of 2.4 × 10-4 S cm-1 and an enhanced Na+ transference number of 0.61 at room temperature. When assembled Na|PANO-SN|Na symmetric cell, the batteries maintain stable Na plating/stripping for over 1200 h at 0.1 mA cm-2 with a stable polarization voltage of approximately 0.4 V. Furthermore, the Na|PANO-SN|NVP full cell delivers an excellent cyclability with 97.8% capacity retention after 400 cycles at 0.5 C. Notably, the fluoroethylene carbonate (FEC) containing deep-eutectic interfacial layer facilitates the generation of a stable NaF and Na3Nrich solid electrolyte interphase (SEI), restraining parasitic side reactions and homogenizing sodiumion flux. This work offers a rational strategy for developing mechanically robust, interfacially compatible, and ionically conductive quasi-solid-state electrolytes for high-performance sodium-metal batteries.