Polyacrylonitrile and Polypropylene Carbonate Blended Solid Polymer Electrolytes for Application Toward Solid State Lithium Ion Batteries

Abstract

Lithium ion batteries are promising as energy storage devices because of their high energy density; however, current technology for lithium ion batteries is not safe for large scale applications and general use. Traditional lithium ion batteries use an organic liquid electrolyte to transport lithium ions between electrodes. Organic solvents used in lithium ion batteries, such as diethyl carbonate, are highly flammable and volatile. Safety issues arise when the battery heats from charging, discharging, or from dendrite formation in the cell. When this occurs, the battery can potentially ignite and pose a safety hazard. In this work, the research focus is developing blended solid polymer electrolytes for solid state lithium ion batteries. Polypropylene carbonate (PPC), an amorphous polymer, and polyacrylonitrile (PAN), a semi-crystalline polymer, have been shown to be individually effective for solid state lithium ion batteries. In this work, we fabricate novel PAN and PPC blended solid polymer electrolytes complexed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Furthermore, LiTFSI acts as both a source of lithium ions and as a plasticizer for the polymers, thus increasing the amorphous character of the polymer blend. Lithium ion conductivity is higher in amorphous electrolytes than in semi-crystalline solid polymer electrolytes. Solution casting, a commonly used technique for electrolyte fabrication, is used to control the thickness of the electrolyte film by varying the amount of solution added to the casting plate. During solution casting, the PPC and PAN undergo phase separation, this increases the number of micro-pores in the electrolyte. It has been shown that micro-pores improve the ionic conductivity of solid electrolytes. Upon evaporative drying of the solid polymer electrolytes, several tests are performed to characterize the electrolyte material as test well as battery performance.