Ion Conduction and Viscoelastic Response of Epoxy-Based Solid Polymer Electrolytes Containing Solvating Plastic Crystal Plasticizer

초록

To develop a safe electrolyte for lithium-ion batteries, solid polymer electrolytes (SPEs) are prepared using a commercially available cross-linkable diglycidyl ether of bisphenol-A (DGEBA) epoxy resin, a methyl tetrahydrophthalic anhydride (MeTHPA) curing agent, and a plastic crystal-based electrolyte containing a mixture of succinonitrile (SN) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) by a simple thermal curing process. For the uncured mixture of DGEBA/MeTHPA/SN/LiTFSI, oscillatory and steady shear measurements are conducted to investigate microstructure and processability; the storage modulus (G) exceeds the loss modulus (G) at all frequencies studied (solid-like behavior) and the viscosity decreases with an increase in the shear rate (shear-thinning behavior), demonstrating that there is a network structure, and the connected structure changes at high shear rates. Fourier transform infrared spectroscopy confirms the physical interactions between Li+ of LiTFSI and anhydride group of MeTHPA, which are responsible for the network structure, and helps to rationalize the observed moduli and viscosity. For the cured epoxy-based SPEs, their ionic conductivities follow the Arrhenius temperature dependence, and increasing SN/LiTFSI electrolyte content leads to higher conductivity and lower activation energy for conduction, resulting in ionic conductivity sigma(DC) approximate to 2 x 10(-4) S cm(-1) with a shear modulus approaching G approximate to 1 MPa at room temperature.

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