Porous polymer electrolyte based on poly(vinylidene fluoride)/comb-liked polystyrene via ionic band functionalization

Abstract

The grafted polymer modified by ionic bond was synthesized by a simple and scalable method based on sulfonated polystyrene (SPS) and the monoamine-terminated PEO derivative (M2070). Porous polymer electrolytes (PPEs) containing the grafted polymer and poly(vinylidene fluoride) (PVDF) were prepared by phase inversion process. The dense pores distributed in the polymer matrix, which could store liquid electrolyte and provide enough channels for ionic conduction, and the ionic conductivity of PPEs was thus improved effectively. Furthermore, the effect of the mass fraction of grafted polymer on porosity, electrolyte uptake, and ionic conductivity was investigated. The PPE membrane with 30 wt% grafted polymer (PPE-3) exhibited the better pore distribution and superior electrolyte uptake compared with pure PVDF membrane, which resulted in the remarkable ionic conductivity (3.05 × 10−3 S cm−1) of the corresponding PPE-3 at 30 °C. The contact angle of PPE-3 (14.9°) decreased significantly owing to the good affinity of grafted polymer with electrolyte. The LiFePO4/PPE-3/Li cell showed a stable charge/discharge performance with initial discharge capacity of 141 mA h g−1 at room temperature and 96% capacity retention after 130 cycles. Those results suggest that PPEs containing the grafted polymer via ionic band can be promising electrolyte candidates for high-performance lithium ion batteries.