Poly(vinylidene fluoride)-Based Al Ion Conductive Solid Polymer Electrolyte for Al Battery

Abstract

Al ion conductive solid polymer electrolyte is prepared using poly(vinylidene fluoride) (PVdF) and AlCl₃ as a host polymer and Al ion salt, respectively. AlCl₃ salt can be dissolved into PVdF and uniformly distributed in the polymer up to F/Al ratio is 8. With further increase in the AlCl₃ content, a phase separation of AlCl₃ and PVdF is observed. It is noted that melting and amorphization temperatures of PVdF are also affected by the content of AlCl₃. The melting temperature and promotion of crystallization of PVdF decrease with increase in AlCl₃ until F/Al to be 8. With further increase in AlCl₃, the melting and crystallization temperature increase. Through FT-IR characterization, it is observed that characteristic frequency peaks relating CF vibration shift with addition of AlCl₃, indicating that Al cation interacts with F in the PVdF host. The highest conductivity is 4.4 × 10⁻⁴ S cm⁻¹ at room temperature is achieved at F/Al ratio equaling 8. The cation transference number of this Al polymer electrolyte is 0.24 which is close to that of PVdF-based Li ion conductive polymer. The electrochemical stable window of the PVdF-AlCl₃ polymer at F/Al ratio of 8 is 0 ∼ 2.4 V vs. Al³⁺/Al. The electrochemical stable window covers redox voltages of most reported cathode materials for rechargeable Al batteries, implying that this PVdF-based polymer electrolyte can be a good candidate for the Al batteries.