Improved Electrochemical Properties of Aqueous Lithium-Ion Batteries Via the Optimization of Gel Polymer Electrolytes

Abstract

Lithium-ion batteries (LIBs) have been developed for their high energy density and long cycle life in military systems. However, the use of non-aqueous electrolytes based on toxic and flammable organic solvents have raised serious safety concerns including fire and explosion in LIBs. Aqueous LIBs with non-flammable and environmental aqueous electrolytes are promising alternative to eliminate the safety issues. Because aqueous batteries use water as a solvent of electrolyte, they are stable with no flammable. However, the narrow electrochemical stability window (ESW) of water in aqueous electrolytes limits operating voltage and energy density of aqueous batteries. Recently, ESW was expanded by applying a high concentration lithium salt electrolyte called “water-in-bisalt” (WIBS). A 4.0 V aqueous LIB was developed by passivating graphite anodes with hydrophobic LiTFSI-HFE gels, which effectively extended electrolyte stability [1].In this study, we developed a 4.0 V aqueous LIBs using UV-cured gel polymer electrolytes. Highly concentrated UV-cured gel polymer electrolytes were coated to cathodes and UV-cured gel protection layers were applied to anode surfaces for improving stability. Also, gel polymer electrolytes were optimized with various lithium salts and additives. We also evaluated cycle performance and safety such as cutting, penetration test with LiMn2O4∥graphite pouch type cells. There were no fires and explosions.