Immobilized cation functional gel polymer electrolytes with high lithium transference number for lithium ion batteries

Abstract The ionic liquid (IL) incorporated hybrid membranes were synthesized via sol-gel process to simultaneously act as a separator and functionalized gel polymer electrolytes (GPEs). These IL functionalized hybrid GPEs provide an adequate ionic conductivity of 6.0 mS cm−1 at 30 °C and good electrochemical stability up to 5.0 V. Moreover, the differential scanning calorimetry (DSC) results demonstrated that the IL group hardened the polymer chain without liquid electrolytes. However, the glass transition temperature (Tg) dramatically decreased when liquid electrolytes were incorporated, which means the polymer has good affinity for carbonate electrolytes and good ionic transport ability. Further, the immobilized cationic group anchored in the polymer matrix can be seen as a Lewis acid; thus, it interacts with the PF6- anion and enhances the lithium transference number from 0.28 to 0.57. In addition, compared to the GEP without the IL group (SiEO), the GPE with high IL group (ImEO51) shows relatively superior battery performance. For the Li/GPE/LiFePO4 battery application, cell capacities of both SiEO and ImEO51 were close to 150 mAh g−1 at 0.1 C. However, at high current density of 5 C, the capacities of ImEO51 can reach 90 mAh g−1, significantly higher than that without the IL group (35 mAh g−1). Therefore, the aforementioned properties of the IL functional GPEs can be a potential alternative polymer electrolyte for high-performance rechargeable lithium ion batteries.