A novel polyhedral oligomeric silsesquioxane based ionic liquids (POSS-ILs) polymer electrolytes for lithium ion batteries

Abstract

A series of novel imidazolium-based polyhedral oligomeric silsesquioxane ionic liquids (POSS-ILs) have been successfully synthesized and used to develop new solid polymer electrolytes with high ionic conductivity and wide electrochemical windows. The POSS-ILs are added to the solid polymer electrolytes (SPEs) based on blend of polyethylene oxide (PEO), poly(vinylidene fluoride-hexafluoro propylene) (P(VDF-HFP)), propylene carbonate (PC) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) to alter the morphology, ionic conductivity, electrochemical windows properties. The results from scanning electron microscope (SEM), energy-dispersive x-ray spectrometry (EDXS) mapping and X-ray diffraction (XRD) indicate that POSS-ILs are uniformly distributed in the SPEs and form amorphous area by significantly inhibiting the crystallization of host polymer. The electrochemical studies indicate that the addition of POSS-ILs increases the ionic conductivity up to 3.9 × 10−4 S cm−1 at 22 °C and 1.5 × 10−3 S cm−1 at 62 °C. The electrochemical windows of POSS-ILs based SPEs are stable up to 5.0 V. As a result, the lithium-ion battery cell prepared using the POSS-ILs-SPE showed a good cycle performance and reversible capacity recovery behavior. These indicate POSS-ILs based SPEs would be good candidate to replace the conventional organic liquid electrolytes for lithium ion batteries.