Electrical and mechanical properties of glass and glass-ceramic electrolytes in the system Li₃BO₃–Li₂SO₄

Abstract

Low-melting oxide glasses are promising as electrolytes for all-solid-state lithium rechargeable batteries. Glasses in the pseudobinary system Li₃BO₃–Li₂SO₄ were prepared by a mechanochemical technique. Raman spectra revealed that the glasses contained no macroanions which form networks but consisted only of Li⁺ ions and two discrete ortho-oxoanions, BO₃³⁻ and SO₄²⁻. The density and molar volume increased and elastic moduli decreased with an increase in the Li₂SO₄ content in the glasses. The heat treatment of the Li₃BO₃–Li₂SO₄ glasses at around 300°C brought about the crystallization to form ion conducting glass-ceramics. Electrical conductivities of the glasses and glass-ceramics in this system were maximized with the mixing of Li₃BO₃ and Li₂SO₄. The conductivities were higher in the glass-ceramics of the compositions with small amounts of Li₂SO₄, ranging from 3 × 10⁻⁶ to 1 × 10⁻⁵ S cm⁻¹ at room temperature, compared to the corresponding glasses. This conductivity enhancement by the heat treatment is probably due to the precipitation of solid solutions with a high temperature Li₃BO₃ phase.