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.