The structures, ionic conductivities and electrochemical stabilities of the (100 - x)(0.7Li(2)S center dot 0.3P(2)S(5))center dot xLiI glass and glass-ceramic electrolytes were investigated. The (100 - x)(0.7Li(2)S center dot 0.3P(2)S(5))center dot xLiI glasses and glass-ceramics were prepared by mechanical milling in the composition range 0 <= x(mol%) <= 20. All the glasses and glass-ceramics had P2S74- and PS34- ions. The Li7P3S11 crystals were observed in all the glass-ceramics. On the other hand, crystals containing PS34- ions were mainly precipitated in the glass-ceramics with increasing the LiI content. The conductivities of glasses increased with increasing the LiI content, and the glass at x=20 showed the highest conductivity of 5.6 x 10(-4) S cm(-1). While the conductivity of glass-ceramics at x=0 was 4.2 x 10(-3) S cm(-1), it decreased sharply with increasing the LiI content. Cyclic voltammetry indicated that the 80(0.7Li(2)S center dot 0.3P(2)S(5))center dot 20LiI glasses exhibited a wide electrochemical stability up to 10 V vs. Li+/Li. (C) 2012 Elsevier B.V. All rights reserved.