Ameliorating the electrode/electrolyte interface compatibility in Li-ion solid-state batteries with plasticizer

Composite solid electrolytes (CSEs) based on poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/LiTFSI/LLZO/different wt% of tetra-ethylene-glycol-dimethyl-ether (TEGDME) were prepared using the facile solution casting method or phase-inversion method. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy measurements were used to identify the structures and complexations of the prepared electrolyte films. The morphology and thermal stability of the electrolytes were investigated using field-emission scanning electron microscopy (FE-SEM) and thermogravimetric analysis (TGA). The ionic conductivity of all electrolyte films was analyzed using AC impedance analysis between 298 and 353 K. The data supports that the 30 wt% TEGDME CSE exhibited the highest ionic conductivity (6.2 × 10–5 S cm–1 at 25 ℃ and 3.6 × 10–4 S cm–1 at 60 ℃) and a wide electrochemical window (4.87 V vs. Li/Li+). A solid-state battery with LiFePO4/Li-metal was cycled using the 0.1 C rate at 60 °C for 100 cycles, resulting in a high initial discharge capacity of 157 mAh g–1 with a good coulombic efficiency of> 99%. This admirable electrochemical performance can be attributed to the high ionic conductivity of the electrolyte and its electrochemical stability. We emphasize the significant role of the TEGDME plasticizer in the performance of the CSE as well as the ionic conductivity and compatibility of the electrolyte with the electrode in the solid-state battery. All encouraging results confirm that the CSE has the potential to be a high-voltage electrolyte for Li-ion solid-state batteries.