Role of dinitrile plasticizer chain lengths in electrochemical performance of highly conductive polymer electrolyte membrane for lithium ion battery

Abstract

The present article entails the effect of chain lengths or number of carbons (n) of dinitrile plasticizers (NC-(CH2)n-CN) in ionic conductivity and electrochemical stability of polymer electrolyte membranes (PEM) containing poly(ethylene glycol diacrylate) (PEGDA) precursor and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) salt. Ternary phase diagrams of PEGDA, dinitrile plasticizers/ionizers such as succinonitrile (SCN, n = 2), glutaronitrile (GLN, n = 3), and adiponitrile (ADN, n = 4) plasticizers, and LiTFSI salt blends were established to provide guidance for photo-curing the amorphous PEM mixtures. The resulting photo-cured PEM networks exhibited very high room-temperature ionic conductivity at the level of 10−3 S/cm. Among them, the GLN-plasticized PEM revealed the highest ionic conductivity (∼2.3 × 10−3 S/cm) with a very wide working temperature window from −80 °C to 60 °C. The electrochemical stability of these dinitrile-plasticized PEM networks was evaluated in half-cell configurations (viz., Li4Ti5O12/PEM/Li and LiFePO4/PEM/Li) using Li4Ti5O12 (LTO) and LiFePO4 (LFP) electrodes by means of potentiostat for cyclic voltammetry and galvanostatic charge-discharge cycling. The effect of chain lengths of the dinitrile plasticizers on the electrochemical performance of the PEM network is discussed.