Novel Sodium–Poly(tartaric acid)Borate-Based Single-Ion Conducting Polymer Electrolyte for Sodium–Metal Batteries

The limitations of conventional organic liquid electrolytes such as sodium dendrite growth, serious side reactions, and liquid leakage hinder the development of sodium–metal batteries (SMBs). In this work, a novel sodium–poly(tartaric acid)borate (NaPTAB) salt with low cost and environmental friendliness was synthesized by an aqueous phase synthesis method. NaPTAB was combined with poly(vinylidene fluoride)–hexafluoropropylene (PVDF–HFP) to form NaPTAB-SM, and then NaPTAB-SM was swelled in the PC solution to obtain a single sodium-ion conductor gel polymer electrolyte (GPE), denoted NaPTAB-SGPE. NaPTAB-SGPE has perfect thermal stability with an initial decomposition temperature of 345 °C, a satisfactory ionic conductivity of up to 0.94 × 10–4 S·cm–1 at room temperature, a wide electrochemical window as high as 5.2 V (vs Na+/Na) at 30 °C, and a high sodium-ion transference number of 0.91 at 60 °C. Except for these satisfying performances, the Na3V2(PO4)3/Na cells assembled with NaPTAB-SGPE present excellent charge–discharge performance and stable cycling capability at high temperatures (60 °C). They also exhibit superior cycling stability compared to the liquid electrolyte cells with 1 M NaClO4 (EC/PC, 1:1, v/v, and 5% fluoroethylene carbonate (FEC)). After cycling, NaF is generated on the polymer electrolyte membrane as observed by 23Na and 19F solid-state NMR, which is more likely responsible for the excellent charge–discharge stability and cycling performance of the battery. These results show that NaPTAB-SGPE is a great potential alternative for solid-state sodium batteries.