Bio-inspired design of electrospun poly(acrylonitrile) and novel ionene based nanofibrous mats as highly flexible solid state polymer electrolyte for lithium batteries

Abstract

All-solid-state polymer electrolytes (ASSPEs) have significant importance in the development of rechargeable lithium batteries with superior safety. Herein, a unique ionene oligomer is synthesized from 1,4-Diazabicyclo [2.2.2] octane (DABCO) and diethylene glycol bis(2-chloroethyl)ether having bis(trifluoromethanesulfonyl) imide (TFSI−) as the anion (PO3TFSI, where, ‘P’ indicates the oligomer and ‘O3′ denotes the 3 oxyethylene units). The ASSPE was fabricated by a straightforward viable procedure involving uniaxial electrospinning of poly(acrylonitrile) (PAN) blended with PO3TFSI and doped with lithium bis (trifluoromethanesulfonyl)imide salt (LiTFSI). The prepared electrospun (PAN/PO3TFSI/LiTFSI) ASSPE presented an intriguing morphology following heat-treatment like the venation found on a leaf blade where the network of veins is responsible for providing support to the entire lamina. The final structure consists of a PAN framework with the ionene oligomer flowing out of and around the fibers, closing the pores of the nanofibrous mat in the process. The ASSPE having such leaf blade inspired veined morphology with closed pores exhibits a high room-temperature ionic conductivity of 1.01 × 10−3 S cm−1, an electrochemical stability window of ∼ 4.6 V, and outstanding thermal stability. The solid-state Li/LiFePO4 (LFP) batteries assembled with the (PAN/PO3TFSI/LiTFSI) ASSPE showed good Coulombic efficiency above 98% when cycled at 0.2C for 100 cycles at both 25 °C and 60 °C. Furthermore, the ASSPE showed potential application in all-solid-state lithium sulfur battery. Additionally, a flexible Li/ASSPE/LFP custom made cell was demonstrated to work even in extremely deformed conditions, such as being folded, crimped and rolled, indicating the high flexibility of the fiber based solid electrolyte.