Highly Safe 100-Wh-class Lithium-ion Battery Using Lithium Bis(trifluoromethanesulfonyl)amide-Tetraethylene Glycol Dimethyl Ether Equimolar Complex-based Quasi-solid-state Electrolyte

Abstract

A highly safe 100 Wh-class laminated lithium ion battery (LIB) was developed. For ensuring safety of the LIB, a liquid electrolyte was quasi-solidified at silica surfaces. For the liquid electrolyte, a solvate ionic liquid (SIL), which is an equimolar complex of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and tetraethylene glycol dimethyl ether (G4), Li(G4)TFSA, was used. For enhancing discharge-rate capability, Li(G4)TFSA was diluted by propylene carbonate (PC). Then, for enhancing cycle life, vinylene carbonate (VC) and hexafluorophosphate anion (PF 6− )based salt were added for forming an solid-electrolyte interphase (SEI) on the graphite negative electrode and an AlF 3 at the surface of the aluminum current collector of the positive electrode, respectively. The assembled LIB exhibited initial discharge capacity of 32 Ah and coulombic efficiency of 76%. Regardless of high energy-type, the developed battery exhibited high discharge capacity of 26.2 Ah at 2 C. Its retention ratio of discharge capacity at the 118th cycle is high, i.e., 96%. The developed LIB (with energy density of 363 Wh L− 1 ) generated neither fire nor smoke in a nail-penetration test. These results suggest that the developed LIB has high safety compared to a LIB comprised of a conventional organic liquid electrolyte.