Elucidating the correlation between the prelithiation concentration of a LixSi anode and performance of all-solid-state lithium–sulfur batteries

Abstract

All-solid-state lithium–sulfur batteries with Li_xSi anodes are evaluated. Cells with Li_3.25Si show voltage noise during cycling even at a high anode-to-cathode capacity (N/P) ratio of 3.0 because of the small overalloying margins (x = 3.25–3.75) above which abnormal lithium plating occurs. Cells with Li_1.0Si show no voltage noise at a low N/P ratio of 1.2 owing to sufficient overalloying margins (x = 1.0–3.75). Low areal capacities (∼1 mA h cm⁻²) are observed regardless of the N/P ratio. This poor performance is ascribed to the formation of a lithium depletion zone in the anode. Cells with Li_1.71Si and an N/P ratio of 2.05 exhibit areal and gravimetric capacities of >3 mA h cm⁻² and >900 mA h g⁻¹, respectively, showing no voltage noise during 190 cycles. In this case, the lithium-ion distribution in the anode after charging is more uniform, and no lithium depletion zone or abnormal lithium plating zone near the interface is observed. Accordingly, the polarization resistance of this anode does not considerably increase after discharge, unlike that of Li_1.0Si. The optimal composition for practical cell design is identified as x = 1.71 and N/P ratio = 2.05, enabling the realization of both high electrochemical performance and chemomechanical stability.