Correlation of structure and ionic-conductivity in phosphate glass using MAS-NMR and impedance spectroscopy: Influence of sodium salt

In the process of diminishing the safety concerns of sodium-ion batteries, the development of glass-based solid electrolyte materials has received adequate interest. Nevertheless, achieving a high ionic-conductivity at room temperature for glass materials remains a challenging task because of the poor correlation between the conductivity and the glass structure. Here, we attempt to understand the effective influence of NaC1 on the structure and ionic-conductivity of the phosphate-based glass network. For this study, xNaCl-(100-x) (31.725 Na2O-12.69 Al2O3-31.725 P2O5-8.46 NaF-5.40 Na2SO4-10 MoO3) glass systems (mol %) were selected, where x = 0, 5, 10, 15, and 20 mol %. To investigate structural changes with the addition of different NaCl concentrations, Al-27, Na-23, P-31 magic angle spinning nuclear magnetic resonance (MAS-NMR), P-31 two-dimensional (2D) phase-adjusted spinning sideband (PASS), and P-31 2D J-resolved NMR techniques and Raman spectroscopic techniques were utilized. Impedance spectroscopy and ac conductivity spectra were used to assess ionic-conductivity and sodium-ion dynamics, respectively. Impedance spectral analysis reveals that the ionic-conductivity of the base glass is increased by 2.4 times (from 1.85 x 10(-7) to 4.44 x 10(-7) S/cm at 373 K) with the addition of 20 mol % of NaCl. Raman spectra confirm the presence of P-O-Mo and the absence of Mo-O-Mo bonds in these glass systems, and P-31 2D J-resolved spectra indicate the absence of P-O-P bonds. Upon increasing the NaCl concentration, significant changes in the shapes of P-31 and Al-27 MAS-NMR spectra were observed, indicating the effective influence of NaCl on the distribution of alumina and phosphorus structural units. Irrespective of the temperature, sodium-ion dynamic studies show that the mean-square displacement < R-2(t(p))> decreases with increasing NaCl concentration up to 10 mol % and then increases with a further increase in NaCl concentration. This investigation aids in understanding the sodium-ion dynamics and the structural information of a multicomponent glass system to enhance the room-temperature conductivity.

Automated summary

In this study, the effective influence of NaCl on the structure and ionic-conductivity of phosphate-based glass network was investigated. It was found that the addition of NaCl can enhance the ionic-conductivity of the glass and affect the distribution of alumina and phosphorus structural units.