Paper-Based Composite Separator with Thermotolerant and Flame-Retardant Sodium Silicate Sheath for High-Performance Sodium-Ion Batteries

In comparison to the well-known separator of lithium-ion batteries (LIBs), there are unique characteristics and requirements for the separator of sodium-ion batteries (SIBs) to affect the electrochemical performance and safety. In this work, a composite separator (AP@NSIO) is successfully fabricated by constructing a fully encapsulated sodium silicate (NSIO) ceramic sheath on the fiber surface of a low-cost, recyclable airlaid paper (AP) matrix using a facile solution immersion method. Due to the comprehensive coating of sodium silicate on the matrix fiber, the prepared AP@NSIO separator not only has excellent mechanical strength and remarkable wettability but also maintains thermal dimensional stability at 250 °C and is nonflammable in flames. Moreover, the AP@NSIO separator exhibits a high porosity of ∼50.6%, an electrolyte uptake of ∼298.9%, an ion conductivity of 2.02 mS cm–1, and a sodium-ion transfer number of 0.91. The Na3V2(PO4)3 (NVP)|AP@NSIO|Na battery has an excellent capacity retention of 94.2% (96.8 mAh g–1) after 300 cycles at a high current density of 5C and maintains almost 100% Coulombic efficiency. These results indicate that the AP@NSIO separator is a potential candidate for application in safe and high-performance SIBs, and a strategy is provided for designing functional separators for SIBs.