Reassessment of Electrical and Dielectric Properties in the Borophosphate Glass System: A Promising Solid Electrolyte for High-Temperature Batteries

This study investigates the conduction mechanism of ternary sodium borophosphate glass 30Na O-(70 - )B O - P O with 0 ≤ ≤ 35 mol % from a different perspective, focusing on previously unreported high-temperature electrical and dielectric properties for potential solid electrolytes in high-temperature batteries. The glass composition with B O /P O = 1 exhibits a conductivity of approximately 10 S/cm at 250 °C. Dielectric analysis supports this improved conduction, showing higher dielectric values and minimal energy dissipation during storage, indicating promising conductivity and favorable dielectric properties. This enhancement is attributed to the large-polaron (QMT) model, deduced from the power law exponent, due to the creation and spreading of lattice distortion of a long-range order with interconnected B -O-P and B -O-P linkages. Contrary to previous results, the glass transition temperature does not vary coherently with the conductivity and activation energy, displaying a discontinuity at 14 mol %. This discontinuity is caused by the initial extreme depolymerization of P O , leading to an increase in nonbridging oxygens (NBOs) within the glass network and forming B -O-P linkages. Despite this, the ionic mobility of Na is continuously enhanced, correlated with the increase in the molar volume. This new perspective highlights the significant impact of both free volume expansion and reduced Coulombic effects on conduction improvement.