AlCl3-induced conductivity enhancement in lithium phosphate glasses

This study examines the effect of AlCl 3 incorporation on the structure and properties of ion-conducting lithium phosphate glasses. Chemical analysis reveals that higher Li 2 O/P 2 O 5 ratios result in a greater retention of Cl – ions during synthesis under ambient atmosphere. Solid-state NMR spectroscopy shows that aluminum incorporation proceeds through the expected replacement of P–O–P linkages by new P–O–Al bonds, whereas the introduction of chlorine produces only subtle apparent structural changes. Impedance spectroscopy further demonstrates that AlCl 3 addition yields higher ionic conductivity than an equivalent amount of Al 2 O 3 , consistent with a positive contribution of Cl – ions. The highest ionic conductivity, 1.6 ×10 -6 S·cm -1 at 25°C, was measured for a glass with a Li 2 O/P 2 O 5 ratio of 1.7 and a chlorine content of approximately 4 mol%. Remarkably, we observed improved conductivity despite the total Li⁺ concentration being diluted through the addition of AlCl 3 to the base lithium phosphate glass. Because solid-state NMR provides no clear evidence of Cl – incorporation into the glass structure, our study suggests that the conductivity enhancement associated with Cl – addition is attributable to changes in the local ionic environment rather than to any significant modification of the glass network. • Chloride anions have been incorporated into lithium phosphate glass through AlCl3 addition • Higher Li2O/P2O5 ratios result in greater retention of chloride anions • Chloride anions provoke an ionic conductivity increase • The increased conductivity does not arise from network depolymerization.