Solid Electrolytes for Sodium Batteries from Molecular Crystals of (Adiponitrile) ₃ NaPF ₆

This study reports the synthesis of (Adpn) 3 NaPF 6 (Adpn = adiponitrile), a molecular crystalline solid electrolyte for sodium-ion batteries. In the crystal structure, sodium ions are coordinated with six nitrile groups from three independent adiponitrile molecules, creating an ion migration channel for sodium ions. The PF 6 − anions are uncoordinated. The molecular crystal has a melting point of 95 °C and recrystallizes upon cooling. The material demonstrates a high ionic conductivity of ∼10 −4 S/cm at room temperature, with grain crossing facilitated by excess adiponitrile at the grain boundaries that selectively enhances sodium-ion migration. Transference number calculations reveal a sodium transference number ( t Na + ) of approximately 0.83, consistent with restricted anion movement along the crystallographic axes, allowing sodium ions to dominate migration. The electrolyte shows remarkable electrochemical stability, with a voltage tolerance of up to 4.5 V, making it a promising candidate for advanced sodium-ion battery applications.