Synthesis, structure and properties of Lithium Single Ion-Conducting Polymer Electrolytes based on PEG 400 and anionic nanoparticles

Lithium conducting polymer electrolytes are strategic materials for the development of advanced lithium batteries. Classical lithium polymer electrolytes consist of organic macromolecules such as polyethers that are doped with inorganic salts such as LiClO4, LiPF6, LiTFSI, etc... These materials usually show good room temperature conductivities (≈10-5- 10-6 S/cm) but low Li+ transference numbers. There are at least two methods that can be used to overcome this problem. The first is to add an inorganic nanofiller to the PEO-lithium salt system. This method can lead to an improvement in both the conductivity and transference number. Another possibility is to covalently bond the anion of the lithium salt to the polymeric matrix to obtain a so-called single-ion polymer electrolyte. Here, a next generation single-ion conducting polymer based on a surface functionalized inorganic filler and PEG400 is presented. In this material, the Li+ counter-ion is linked to the filler nanoparticle surface and PEG400 acts to promote Li+ migration between the filler nanoparticles. The filler can be considered a salt with a nanoparticle-like anion that functions as a single-ion conductor. The synthesis and characterization of several single-ion conducting polymer electrolytes obtained by doping anhydrous PEG400 with different amounts of a lithium-functionalized fluorinated TiO2 (TiO2FLi) is described. The aim of this study is the understanding of the TiO2 (TiO2FLi)---PEG400 interactions, the events involved in the conduction mechanism, particularly in terms of the cation and macro-anion coordination sites, and the secondary structure of the PEG400 polymer chains. These studies are carried out by FT-IR and Raman spectroscopy, DSC, TGA and electrochemical methods.