Compliant polymer network-mediated fabrication of a bendable plastic crystal polymer electrolyte for flexible lithium-ion batteries

Abstract

We demonstrate a bendable plastic crystal polymer electrolyte (referred to as "B-PCPE") for use in flexible lithium-ion batteries. The B-PCPE proposed herein is composed of a plastic crystal electrolyte (PCE, 1 M lithium bis-trifluoromethanesulphonimide (LiTFSI) in succinonitrile (SN)) and a UV (ultraviolet)-cured polymer network bearing long linear hydrocarbon chains (here, trimethylolpropane propoxylate triacrylate (TPPTA) polymer is exploited). The solid electrolyte characteristics of the B-PCPE are investigated in terms of plastic crystal behavior, mechanical bendability, ionic conductivity, and cell performance. Owing to the presence of long linear hydrocarbon chains attached to crosslinkable acrylate groups, the TPPTA polymer network in the B-PCPE acts as a compliant mechanical framework, thereby exerting a beneficial influence on bendability and also interfacial resistance with lithium metal electrodes. Meanwhile, the B-PCPE exhibits slightly lower ionic conductivity than a control sample (referred to as "R-PCPE") incorporating a rigid and stiff polymer network of ethoxylated trimethylolpropane triacrylate (ETPTA). This unique behavior of the B-PCPE is discussed with an in-depth consideration of the polymer network structure and its specific interaction with the lattice defect phase of SN in the PCE. Although relatively sluggish ionic transport is observed in the B-PCPE, its intimate interfacial contact with electrodes (possibly due to the mechanically compliant TPPTA polymer network) may beneficially contribute to imparting satisfactory cycling performance.