A coordination-reinforced and encapsulated polymer electrolyte for durable and safe Na-metal batteries

• A novel gel electrolyte was designed with synergistic encapsulation and coordination. • SN-bridged hydrogen-bond network links TMP solvation structure and facilitates fast ion transport. • The electrolyte features high conductivity (0.10 mS cm −1 at −20°C), a wide electrochemical window (>4.5 V), and unprecedented interfacial stability (>1500 h). • Full batteries show exceptional cycling stability at both 2C (>1000 cycles) and −10°C (>700 cycles). Gel polymer electrolytes (GPEs) are a promising alternative to flammable organic electrolytes for Na-metal batteries (NMBs). However, their utilization is hindered by interfacial instability and reduced ionic conductivity, particularly at low temperatures. This work presents a molecular engineering strategy that improves electrolyte performance through molecular coordination and physical encapsulation. An encapsulated gel polymer electrolyte (EGPE) is created by confining sodium bis(trifluoromethanesulfonyl)imide, succinonitrile (SN), and trimethyl phosphate (TMP) within a poly(vinylene carbonate) network formed via in situ polymerization. This network not only provides effective encapsulation by physically immobilizing reactive liquid components for enhanced interfacial stability but also facilitates hydrogen bonding between SN and TMP, enabling efficient ion transport. This approach yields good ionic conductivities (0.10, 0.23, and 0.78 mS cm −1 at −20, 0, and 40°C), a low activation energy (0.24 eV), and stable interfacial performance, with interfacial impedance remaining stable over 30 days and 1500 h of cycling in Na|EGPE|Na symmetric cells. Na|EGPE|Na 3 V 2 (PO 4 ) 3 cells also show stable cycling, reaching 82.2 mAh g −1 after 1000 cycles at 2C (25°C) and 99.3 mAh g −1 after 700 cycles at 0.2C (−10°C).