Effects of surfactant addition to polyethylene oxide polymer electrolytes in low and high concentrations

Abstract

The effect of surfactant addition to polyethylene oxide (PEO) polymer electrolytes is studied. The initial goal of the research was to determine if a self-assembled monolayer (SAM) of surfactant molecules could be formed at the polymer interfaces through what we describe as the “blooming” method. In this method, the surfactant is added to the polymer solution before casting and the surfactant migrates to the surface, due to differences between bulk and surface free energies, during removal of the solvent as the film is formed. The surfactant used had the chemical formula of H–(–CH2–)32–(–CH2–CH2–O–)10–H where the hydrocarbon part of the molecule has the ability to self-assemble once they reach the surface of a PEO polymer electrolyte. These molecular surface layers stabilized the SEI layer formed between lithium metal and the polymer electrolyte. At a level of 8% by mass and above, there was significant interfacial stabilization. In addition to interface stabilization, it was found that the addition of the surfactant caused significant changes to the bulk of the polymer, yielding an order of magnitude higher conductivity in the bulk phase. The structure of the protective film at the surface was investigated by ATR-FTIR spectroscopy and AFM phase imaging.