New oligoether plasticizers for poly(ethylene oxide)-based solid polymer electrolytes

Two new plasticizers, nitrile groups terminated oligoether (NOE) and lithium sulfonamide groups containing oligoether (LSA), have been synthesized to construct superior poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs). The chemical structures of these plasticizers were confirmed by FTIR, 1H-NMR, and elemental analysis. The electrochemical and thermal properties of the resulting SPEs have been thoroughly evaluated. The SPEs containing varied weight ratios of these plasticizers along with different Li/O mole ratios of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) have been investigated to optimize the electrolyte systems. Both plasticizers displayed good ionic conductivity at elevated temperatures. The SPE containing 40 wt.% of NOE in 12:1 PEO-LiTFSI complex showed ionic conductivity of 1.11 × 10−4 S cm−1 at 312 K, while the SPE containing 10 wt.% of LSA in 12:1 PEO-LiTFSI complex showed 5.08 × 10−5 S cm−1 and 1.88 × 10−4 S cm−1 at room temperature and 312 K, respectively. Most notably, the SPE containing 10 wt.% LSA in 14:1 PEO-LiTFSI complex displayed ionic conductivity of 1.01 × 10−3 S cm−1 at 343 K. Moreover, these SPEs exhibited good electrochemical stability (~ 4.2 V vs. Li+/Li) and displayed no noticeable thermal degradations below 350 °C.