Sulfide-Based Hybrid Solid Electrolytes for All-Solid-State Lithium-Ion Batteries

All-solid-state lithium batteries (ASSLBs) with sulfide electrolytes have attracted considerable attention owing to their enhanced safety and high energy density. The successful development of ASSLBs relies on resolving the many issues related to solid electrolytes. The brittleness of solid electrolyte pellets prepared by pressing sulfide powder makes it difficult to prepare a thin sheet. Therefore, typical sulfide-based solid electrolytes used in ASSLBs have a thickness of more than 500 μm to prevent mechanical breakage of the pellet, which leads to a decrease in the ionic conductance and energy density of the ASSLB. Moreover, making an electrolyte pellet by cold pressing results in formation of numerous voids in the solid electrolyte, which blocks ion transfer in the electrolyte. In addition, the high interfacial resistance between the solid electrolyte and composite electrodes caused by poor solid-solid interfacial contacts deteriorates the cycling performance of ASSLB. To date, rubber-based polymer binders have been commonly used to prepare sheet-type thin electrolyte sheet. However, rubber-based binders significantly reduce the ionic conductivity. Herein, we prepared thin and robust sheet-type electrolytes using an ion-conducting cross-linking agent. The cross-linking reaction allowed the three-dimensional network structure of sulfide electrolyte, resulting in enhancement of mechanical strength of the electrolyte. In addition, a cross-linked sheet exhibited high flexibility that enables roll-to-roll processing. The sheet-type cross-linked solid electrolyte was applied to all-solid-state lithium-ion cell (graphite/LiNi_xCo_yMn_1-x-yO₂), and its electrochemical performance was evaluated and compared with that of a cell employing a sheet-type solid electrolyte treated with rubber-based binders.