A nano-SiO₂ embedded HPC/P(VDF-HFP) composite gel membrane for fast-charging sodium metal batteries with long span life

Sodium metal batteries (SMBs) are highly promising for the next generation of rechargeable batteries due to their affordability and high specific capacity. However, practical application faces several challenges, including the formation of sodium dendrites and the instability of the solid electrolyte interphase (SEI), etc. To address these issues and enhance SMBs' cycle life, gel polymer electrolytes (GPEs) have shown effectiveness. In this study, a composite gel membrane is prepared by blending hydroxypropyl cellulose (HPC) and P(VDF-HFP) matrix with SiO₂ nanoparticles. The addition of biodegradable HPC reduces reliance on fossil-based materials, while SiO₂ enhances the composite's ionic conductivity. The resulting GPE, named HPC/PVH-SiO₂, demonstrates superior properties: high mechanical strength (14.4 MPa), wide thermal and electrochemical stability, good ionic conductivity (0.587 mS cm⁻¹), and notable Na⁺ transference number (0.52). These properties are essential for ensuring uniform deposition of sodium ions and safeguarding the sodium metal electrode. Additionally, SMBs assembled with HPC/PVH-SiO₂ exhibit remarkable cycling stability and rate performance, with a capacity retention rate of 99.2% and Coulombic efficiency of nearly 100% after 5000 cycles at a high rate of 20 C. This research significantly boosts the potential applications and commercialization of SMBs.