Ionic Conductivity of Composite Solid Electrolytes (C₄H₉)₄NBF₄–Al₂O₃

Composite solid electrolytes (C₄H₉)₄NBF₄–Al₂O₃ are synthesized in a wide range of composition. Their thermal, structural, and conducting properties are studied. The conductivity of the composites passes through a maximum at x ~ 0.9 and reaches 7.2 × 10^–4 S/cm at 150°C for the 0.1(C₄H₉)₄NBF₄–0.9Al₂O₃ composite. The absence of thermal effect at the melting temperature of the ionic salt and the absence of peaks of tetrabutylammonium tetrafluoroborate in the diffraction pattern for a composite, which exhibits a high ionic conductivity, indicate that at x ≥ 0.9, (C₄H₉)₄NBF₄ is in the amorphous state, and ionic transfer occurs along the ionic salt/oxide interface.