Separator-Free Hybrid Electrolytes Composed of Inorganic, Polymer and Liquid Electrolyte for Lithium-Ion Batteries with Enhanced Safety

Lithium-ion batteries have rapidly become the dominant power sources for portable electronic devices and electric vehicles.  However, safety issues still prevent full utilization of these batteries owing to the use of flammable liquid electrolytes, and safety problems have become a significant concern especially in large capacity applications such as electric vehicles and energy storage systems.  In this respect, fabrication of solid-state lithium batteries by using inorganic solid electrolytes may give a fundamental solution for the safety issue of lithium batteries.  However, sheet manufacturing, especially using thin-film technologies for making large-scale batteries, is considered to be difficult because of hard and brittle ceramic materials.  In this work, flexible hybrid electrolytes composed of inorganic electrolyte with polymer binder and liquid electrolyte were prepared in the form of flexible film, and their electrochemical characteristics were investigated.  An addition of small amount of liquid electrolyte significantly improved ionic conductivity and interfacial properties between electrodes and electrolyte.  The optimized hybrid electrolyte was applied to the graphite/LiCoO₂ pouch cells and their electrochemical performances were evaluated.  The enhancement of battery safety was confirmed at the cell level by various techniques such as Accelerating Rate Calorimetry (ARC).