Quasi-Solid Polymer Electrolyte with Multiple Lithium-Ion Transport Pathways by In Situ Thermal-Initiating Polymerization.

Abstract

Solid polymer electrolytes (SPEs) are considered to be attractive candidates for rechargeable batteries on account of their high safety and flexible processability. However, the restricted polymer segmental dynamics limit the Li+ conduction of SPEs. Herein, a composite electrolyte membrane was prepared via in situ thermal-initiating polymerization of diethylene glycol diacrylate (DEGDA) in a poly(vinylidene fluoride) frameworks (PVDF FMs) electrospun in advance. As a quasi-solid polymer electrolyte (QSPE), it provides multiple transport highways for Li+ built by the C═O or C-O or C═O/C-O groups in poly(diethylene glycol) diacrylate (PDEGDA), respectively, proved by density functional theory calculations together with the high-resolution 7Li solid-state nuclear magnetic resonance spectra. Since the interaction between Li+ and C═O is weaker than that between Li+ and C-O, Li+ tends to move along C═O dominating paths in PDEGDA/PVDF FMs QSPEs, even skipping back to C═O nodes from the original C-O dominating way. Multiple transport patterns facilitate Li+ migration within PDEGDA/PVDF FMs QSPEs, contributing to the ionic conductivity of 1.41 × 10-4 S cm-1 at 25 °C and the Li+ transference number of 0.454. Ascribing to the wetting capability of the monomer to the electrodes in use, compatible electrolyte/electrode interfaces with low interface resistance and compact cells were acquired by the in situ polymerization. Protective lithiated oligomers (RCOOLi) and LiF are enriched at the Li anode surface, promoting a lasting stable Li plating/stripping over 2000 h. By applying the QSPEs in LiFePO4 cell, a capacity of 157.7 mAh g-1 with almost 100% coulombic efficiency during 200 cycles is achieved at 25 °C.