Single Sodium-Ion Conducting Borate-Based Polyeugenol Electrolyte for Energy Storage Devices

The development of sodium-metal batteries (SMBs) is hindered by several limitations associated with conventional organic liquid electrolytes. In this study, we report the synthesis of a novel sodium polyeugenol borate (Na-PEB) salt, which offers low cost and environmental sustainability, synthesized via a cationic polymerization method. Na-PEB was then combined with poly(ethylene glycol) (PEG) 4000 to form the Na-PEB-PEG composite electrolyte. Na-PEB-PEG has perfect thermal stability with an initial decomposition temperature of 376 °C, a satisfactory ionic conductivity of up to 1.5 × 10–5 S/cm at room temperature, a wide electrochemical window as high as 2.3 V, and a high sodium-ion transference number of >0.96 at 30 °C. It also shows the diffusivity constant in the order of 10–6 m2/s and ionic mobility in the order of 10–8 m2 v–1s–1 at 30 °C. The electrolyte matrix shows a low energy requirement of ionic transport, i.e., 0.266 eV. On behalf of these findings, Na-PEB-PEG-based semisolid polymer electrolyte confirms its potential for application in sodium-ion-based energy storage systems.