Development of high performing polymer electrolytes based on superconcentrated solutions

Abstract In this work, we investigate gel-polymer electrolytes (GPEs) made of porous PVDF-HFP swollen by concentrated solutions of LiTFSI salt in DMC:FEC mixtures. The porous nature of the polymer matrix allows achieving high values of electrolyte uptake while keeping adequate mechanical stability. As a result, the ionic conductivity values of the different gels were high, ranging between 10−5 and 10−4 S cm−1 at room temperature with the highest value (0.19 mS cm−1) being obtained for the superconcentrated gel electrolyte named GPE-211 having a molar ratio composition of 2:1:1 (DMC:FEC:LiTFSI). The lithium transference numbers (t+) were also found to be high, higher than 0.4 in some cases. Moreover, the electrochemical stability window of these gels exceed 5V in all cases, and aluminium corrosion was hindered. Stability tests were carried out for optimized gel electrolyte (GPE-211), showing that plating/stripping in symmetrical Li/Li cells is stable for more than 300 h, whereas coulombic efficiency in Li/Cu cells reaches over 80%. Finally, Li/GPE-211/LFP and Li/GPE-211/NMC batteries were assembled and tested, obtaining high capacity values (147 mAh g−1 and 160mAh g−1 at 0.1 mA cm−2) and good rate capability at room temperature.