Solid polymer electrolytes (SPEs) in lithium batteries have the dual function of electrolyte and separator to hinder lithium dendrite growth that causes hazardous short circuits during repeated charge/discharge cycles [1]. Polyethylene oxide (PEO), together with a lithium salt, would be a promising candidate as SPE for its good electrochemical and mechanical properties, but its low ionic conductivity at room temperature limits its use. In the last years the attention has been focused on gel polymer electrolytes (GPEs) for the high ionic conductivity at room temperature, good mechanical properties and safety improvements [2]. GPEs can consist of a flexible polymeric matrix as supporting network and a liquid phase containing a lithium salt [3]. Several polymers, like polyvinylidene difluoride (PVdF) for the high dielectric constant and the good electrochemical stability, and PEO have been used as matrix for GPEs.

Given the good compatibility between PVdF and PEO and with the aim to merge the properties of these two polymers, we prepared and characterized PVdF/PEO membranes that act as separators and as hybrid gel polymer electrolytes (HGPEs) when soaked in the liquid solvent with lithium salt. The membranes based on the polymer blends were prepared by electrospinning, a technique that yields micro-nanofibrous membranes with high porosity and, hence, huge values of electrolyte uptake [4]. PEO 100,000 and PEO 1,000,000 were used to prepare two blends with PVdF:PEO 90:10 w/w composition. Such membranes were soaked in 1M LiPF₆ – ethylene carbonate:dimethyl carbonate (1:1 w/w) and the electrochemical performance of these HGPEs were tested in a Li/HPGE/LiFePO₄ cell and discussed on the basis of their physical, mechanical, thermal and morphological properties.

Acknowledgments

Alma Mater Studiorum –Università di Bologna is acknowledged for RFO financial support

References

[1] Croce, F.; Focarete, M. L.; Hassoun, J.; Meschini, I.; Scrosati, B. Energy Environ. Sci. 2011, 4, 921-927

[2] Manuel Stephan, A. European Power Journal 2006, 42, 22.

[3] Marcinek, M.; Syzdek, J.; Marczewski, M.; Piszcz, M.; Niedzicki, L.; Kalita, M.; Plewa-Marczewska, A.; Bitner, A.; Wieczorek, P.; et al. Solid State Ionics 2015, 276, 115.

[4] Zaccaria, M.; Fabiani, D.; Cannucciari, G.; Gualandi, C.; Focarete, M. L.; Arbizzani, C.; De Giorgio, F.; Mastragostino, M. J. Electrochem. Soc. 2015, 162, A915.