Structure and Ionic Conductivity of Li2S-P2S5-P2O5 Glasses and Glass-Ceramics Prepared by Mechanical Milling

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Lithium ion conducting Li2S-P2S5-based solid electrolytes with P2O5 and Li2O as an oxygen source were synthesized by the mechanical milling method. P2O5 effectively reacted with Li2S-P2S5 compared to Li2O. 31P MAS-NMR spectroscopy revealed that the 80Li2S•18P2S5•2P2O5 (mol%) glass included POnS4-n (n=1, 2, 3) tetrahedral units where phosphorus was coordinated with both sulfurs and oxygens. The 80Li2S•19P2S5•1P2O5 (mol%) glass attained a minimum value of the glass transition and crystallization temperatures. In addition, the glass exhibited high ambient temperature conductivity of 1.7×10-4 S•cm-1 and low activation energy of 36 kJ•mol-1 for conduction which were comparable to the glass without P2O5. Further increase in P2O5 to the Li2S-P2S5-P2O5 glasses led to a decrease in conductivities at room temperature and an increase in activation energies. The higher conductivity and lower activation energy for conduction of the 80Li2S•(20-x)P2S5•xP2O5 (mol%) glass-ceramics compared to those of the corresponding glasses were caused by the fact that the highly conductive thio-LISICON analog phase was precipitated by heating of the glass over the crystallization temperature.
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