Electrical and mechanical properties of Na2.8Ca0.1Al2Ga0.5P2.7O12 glass based electrolyte materials: Influence of Ag+ ion-exchange

Sodium super ionic conductor (NASICON) based glass is emerging as solid electrolyte material for Na-ion batteries. In the present study, we report the influence of Ag+ → Na+ ion-exchange process on the electrical, optical, structural and mechanical properties of NASICON type glass with a chemical formula of Na2.8Ca0.1Al2Ga0.5P2.7O12 (NCAGP). Ag+ ion exchange process was carried out by dipping NCAGP glass in AgNO3 molten salt at 300 °C for 15 min (IE15min) and 30 min (IE30min). The diffusion depth of Ag+ ions was measured to be about ~7 μm and ~25 μm for IE15min and IE30min samples, respectively. The dc conductivity values were obtained from base (NCAGP), IE15min and IE30min bulk glass samples through the complex impedance plots at a temperature range of 75 °C-200 °C. With the increase in ion-exchange time, the dc conductivity slightly diminished on account of marginally increase in activation energy (Ea) values. Optical absorption spectra for 30 min ion-exchanged glass revealed the localized surface plasmon resonance (LSPR) band, confirming the reduction of Ag+ ion to Ag0 metal with an increase in ion-exchange time from 15 min to 30 min. Presence of Raman vibrational peak at 233 cm−1 has also confirmed the formation of AgO bonds. The mechanical hardness values obtained through Vickers indentation method reveal enhanced hardness and crack resistance of bulk glasses with the ion-exchange treatment by causing compressive stress on the surface of NCAGP glass. The threshold load for the crack generation is increased from 0.5 kgf (4.9 N) to 2 kgf (19.6 N) after the ion-exchange treatment. Overall, improved mechanical and good electrical properties reveal the applicability of IE15min NCAGP glass as an electrolyte material for Na-ion batteries.