Synthesis of an AlI3-doped Li2S positive electrode with superior performance in all-solid-state batteries

Abstract

A (100 − x)Li₂S·xAlI₃ (0 ≤ x ≤ 30) positive electrode was prepared by the planetary ball-milling method for application in all-solid-state Li–S batteries. X-Ray diffraction results showed that I⁻ in AlI₃ dissolved into the Li₂S structure in (100 − x)Li₂S·xAlI₃ with x ≤ 5 to form the solid solution. The change of the electronic structure of Li₂S and AlI₃ was further proved by UV-Vis spectroscopy and X-ray photoelectron spectroscopy results. The highest conductivity of about 6.0 × 10⁻⁵ S cm⁻¹ at room temperature was obtained with 80Li₂S·20AlI₃ (mol%) and the highest conductivity at 150 °C of about 7.0 × 10⁻³ S cm⁻¹ was observed in 75Li₂S·25AlI₃. The maximum capacities of the cells with x = 0, 0.5, 1.5, and 2 were 880, 1059, 1006, and 869 mA h g⁻¹ Li₂S, respectively. The capacity retention of the cells with x = 0, 0.5, 1.5, and 2 after 60 cycles was 64.0%, 88.4%, 69.6%, and 71.2%, respectively. This study showed that AlI₃ doping could improve not only the conductivities of Li₂S but also the cyclic properties of all-solid-state Li–S batteries.