Chemically bonding inorganic fillers with polymer to achieve ultra-stable solid-state sodium batteries.

Inorganic/organic composite solid electrolytes (CSEs) have attracted ever-increasing attentions due to their outstanding mechanical stability and processibility. However, the inferior inorganic/organic interface compatibility limits their ionic conductivity and electrochemical stability, which hinders their application in solid-state batteries. Herein, we report a homogeneously distributed inorganic fillers in polymer by in-situ anchoring SiO2 particles in polyethylene oxide (PEO) matrix (I-PEO-SiO2). Compared with ex-situ CSEs (E-PEO-SiO2), SiO2 particles and PEO chains in I-PEO-SiO2 CSEs are closely welded by strong chemical bonds, thus addressing the issue of interfacial compatibility and realizing excellent dendrite-suppression ability. In addition, the Lewis acid-base interactions between SiO2 and salts facilitate the dissociation of sodium salts and increase the concentration of free Na+. Consequently, the I-PEO-SiO2 electrolyte demonstrates an improved Na+ conductivity (2.3 × 10-4 S cm-1 at 60 °C) and Na+ transference number (0.46). The as constructed Na3V2(PO4)3 ‖ I-PEO-SiO2 ‖ Na full-cell demonstrates a high specific capacity of 90.5 mAh g-1 at 3C and an ultra-long cycling stability (>4000 cycles at 1C), outperforming the state-of-the-art literatures. This work provides an effective way to solve the issue of interfacial compatibility, which can enlighten other CSEs to overcome their interior compatibility.