Passerini polymerization as a novel route for high ionic conductivity solid polymer electrolyte

[Display omitted] •Novel route for the preparation of polymer electrolytes.•Low crystallinity of modified PEG-based solid polymer electrolytes.•High lithium ionic conductivity, wide electrochemical window (4.6 V) and high specific capacity retention.•Improved flame retardancy. Polyethylene glycol (PEG) used as solid polymer electrolyte has shown disadvantages of low ionic conductivity and lithium ion transference number due to its high crystallinity. In this study, we propose Passerini three-component polymerization (P-3CP) to modify PEGs for solid polymer electrolytes (SPEs). Thus, a series of PEG-based polyesters (PGPEs) with molar masses between 14,400 and 30,200 gmol−1 are synthesized by P-3CP. The crystallinity of obtained PGPEs is successfully suppressed by the introduction of side groups via P-3CP. SPEs consisting of PGPEs as matrix and bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) with different concentrations were investigated in detail. The SPE composed of PGPE-4000 with 30 wt% LiTFSI presented the best ionic conductivities of 5.85 × 10-5 Scm−1 and 1.94 × 10-3 Scm−1 at room temperature and 80 °C, respectively, which are significantly higher than the commonly used PEG-based SPE. The LiFePO4/Li solid-state lithium-ion battery assembled with PGPE-based SPE showed excellent cycle stability. After 100 cycles at 0.5C at 60 °C, the discharge specific capacity remains 133 mAhg−1. Furthermore, due to the addition of amide side groups, the flame retardant property of PGPE-based SPEs is improved. Compared to PEG, the limiting oxygen index (LOI) values increase from 21.0 to 25.5 after modification by P-3CP. Therefore, the P-3CP is an attractive method to obtain polyesters from dicarboxylic acid or diol monomers for the application in the lithium battery field.