Study of Carbamate-Modified Disiloxane in Porous PVDF-HFP Membranes: New Electrolytes/Separators for LithiumIon Batteries

A gel electrolyte membrane is obtained through the absorption of a carbamate-modified liquid disiloxane-containing lithium bis(trifluoromethane) sulfonimide (LiTFSI) by using macroporous poly(vinylidene fluoride-hexafluoropropylene) (PVDFHFP) membranes. The porous membranes are prepared by means of a phase inversion technique. The resulting gel electrolyte membrane is studied by using differential scanning calorimetry, Fourier-transform infrared (FTIR) spectroscopy, and microscope mapping through coherent anti-Stokes Raman scattering (CARS) confocal microscopy and impedance spectroscopy. The ionic conductivity of the gel electrolyte is 10(-4) Scm(-1) at 20 degrees C. FTIR spectroscopy reveals interactions between LiTFSI and the carbonyl moiety of the disiloxane. No in-teractions between LiTFSI and PVDF-HFP or between disiloxane and PVDF-HFP are detected by FTIR spectroscopy. Furthermore, the distribution of the a and b/g phases of PVDF-HFP and the homogeneous distribution of disiloxane/LiTFSI in the gel electrolyte membranes are examined by FTIR mapping. CARS confocal microscopy is used to image the three-dimensional interconnectivity, which reveals a reticulated structure of macrovoids in the porous PVDF-HFP framework. Owing to properties such as electrochemical and thermal stability of the disiloxane-based liquid electrolyte and the mechanical stability of the porous PVDF-HFP membrane, the gel electrolyte membranes presented herein are promising candidates for applications as electrolytes/separators in lithium-ion batteries.