Enhancement of interfacial sodium ion transport stability in quasi-solid-state sodium-ion batteries using polyethylene glycol

Abstract

Poor electrode/solid electrolyte interface stability and dendrite growth have seriously hindered the widespread application of solid-state sodium-ion batteries with high energy density, low cost, and high safety. Herein, a facile strategy is proposed to stabilize the interfacial layer and inhibit dendrite growth using a polyethylene glycol (PEG)-modified poly(vinylidene fluoride-co-hexafluoropropylene)-in-NASICON (Na₃Zr₂Si₂PO₁₂) quasi-solid electrolyte (QSE). PEG enhances the coordination strength between Na⁺ and solvent molecules, and inhibits the volatilization of the solvent. The “sodiophilic” –OH functional group improves the wettability of the QSE surface to sodium metal and inhibits the dendrite growth, thereby constructing a stable interfacial ion transport channel. The room temperature ionic conductivity of QSE with 5% PEG content is 2.4 × 10⁻⁴ S cm⁻¹, and has a high Na⁺ transference number of 0.84. In addition, the Na||Na battery exhibits stable sodium deposition/stripping capability at a current density of 0.2 mA cm⁻² for 3000 h without dendrite growth. The initial discharge specific capacity of the Na||Na₃V₂(PO₄)₃ battery at 1C current density is 100.3 mA h g⁻¹, and the capacity retention rate after 200 cycles is up to 94%. The mechanism of action of a PEG-modified QSE was determined, which provides a reference for the rational design and optimization of QSEs.