Lithium Metal Batteries Operating at Room Temperature Based on Different PEO-PVdF Separator Configurations

Abstract

Gel polymer electrolyte (GPE) membranes based on two polymers, the polyethylene oxide (PEO) and a copolymer of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), and a plasticizer, the dibutylphthalate (DBP), were elaborated in two ways. First, the polymers and the plasticizer were mixed together to obtain a single membrane. Second, a bilayer separator membrane was made by adjunction, through lamination, of a DBP plasticized PVdF-HFP film and a homemade DBP-PEO thin film. The physicochemical properties of the gels were analyzed. AC impedance spectroscopy was carried out on symmetric Li/GPE/Li cells using either the single layer or bilayer membrane as a function of aging (isothermal at 20 and 70°C), temperature (−40 to 70°C), and finally, galvanostatic cell polarization. Both GPE membranes exhibit high ionic conductivities, but the most spectacular result was the measured decrease in the interface resistance, indicative of a deep modification of the interface Li/GPE when the cells were polarized. Aside from having a good interface with the Li metal electrode, such membranes were also shown to form good interfaces with the cathode because assembled flat cells were able to sustain, at room temperature, more than 80% of their initial capacity for more than 300 cycles. © 2004 The Electrochemical Society. All rights reserved.