Dual effect of MgS addition on li2s ionic conductivity and all-solid-state Li-S cell performance

The effect of a multivalence cation, i.e. Mg2+, on both the ionic conductivity of Li2-2xMgxS (0.05 <= x <= 0.2) and the all-solid-state Li-S cell performance employing Li2-2xMgxS as an active material is investigated. MgS was added to Li2S (Li2-2xMgxS) using the planetary ball milling method. No trace of MgS was detected by X-ray diffraction (XRD) with x <= 0.05. Improvement of the ionic conductivity upon addition of MgS was observed even in the samples with 0.05 <= x <= 0.2, where the remaining MgS was detected by XRD analysis. Vacancy formation and the nanoionic effect were the governing factors for Li+ conduction. Stabilization of the cycle capacity was also achieved in the cell containing Li1.2Mg0.15S when compared with that employing bare Li2S as the electrode active material. Improvement of the ionic conductivity by approximately 2 orders of magnitude at 90 degrees C was obtained with x=0.15 compared with that with x=0. In addition, the charge-discharge capacities of the cell with x= 0.15 were stable up to 50 cycles, while the cell with x= 0 began to degrade after the 25th cycle.