Polymer Electrolytes for High Voltage Li-ion Batteries

Solid Polymer electrolytes have been prepared for their application in high voltage lithium batteries (up to 4V). The electrolytes are composed of a matrix of Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with an ionic liquid (PYR13TFSI) and a lithium salt (LiTFSI) in different concentrations. A surface-modified sepiolite with D-α-Tocopheryl polyethylene glycol 1000 succinate (TPGS) has been used to increase the compatibility between the polymer matrix and the liquid phase. The mixtures have been processed by melt compounding obtaining heterogeneous samples with different degrees of phase separation depending on the composition. A systematic study of the morphology and structure of the samples has been carried out by DSC, FTIR, AFM and SEM. The mechanical properties, the ionic conductivity and the ion diffusivity have been studied as the most important requirements of a solid electrolyte. The result is a set of electrolytes with controlled phase separation, which provides a solid behavior with conductivities close to 0.2 mS/cm at room temperature and high values of Li diffusion coefficient.