Preparation And Performances Of Novel Polymer Electrolytes Based On PVDF-HFP/HPMC For Lithium-ion Battery

At present, polymer lithium ion batteries have been widely used in many fields of life because they have good security and stability. As the core of polymer lithium ion batteries, polymer electrolytes have been widely concerned. Aiming at the shortcomings of polymer electrolytes, such as low ionic conductivity and poor mechanical properties, polymer electrolytes based on the blending of poly (vinylidene fluoride-hexafluoropylene)(PVDF-HFP) and hydroxypropyl methyl cellulose (HPMC) were prepared by direct evaporation method and phase transfer method, respectively in this paper. The salicylic acid and tetramethylene sulfone were added to improve the performance of polymer electrolytes. The structures and performances of the polymer electrolytes were characterized and measured by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, linear sweep voltammetry, electrochemical impedance spectroscopy, and charge/discharge test.The performances of polymer electrolytes prepared by the two methods were investigated respectively and compared. The results show that the polymer electrolyte prepared by direct evaporation method has good comprehensive performances when HPMC ratio (w/w) is20%. The electrochemical stability window is up to5.0V, the interface performance is stable, the initial discharge specific capacity is108.6mAh/g when LiMn2O4is used as the anode and the cycling performance is good, but the ionic conductivity at room temperature is only0.382×10-3S/cm. When HPMC is5%, the polymer electrolyte prepared by phase transfer method has good comprehensive performances. The ionic conductivity at room temperature is up to4.168×10-3S/cm, but the electrochemical stability window is only4.5V, the interface performance is not stable, initial discharge specific capacity is101.6mAh/g when LiMn2O4is used as the anode and the cycling performance is poor. The direct evaporation method is more suitable for the preparation of polymer electrolytes based on PVDF-HFP/HPMC. The performances of polymer electrolytes with two additives were investigated respectively and compared. The results show that salicylic acid can significantly improve the performances of the polymer electrolyte and the polymer electrolyte with10%salicylic acid has good comprehensive performances. The ionic conductivity is2.1×10-3S/cm, the electrochemical stability window is up to5.5V, the discharge specific capacity is112.5mAh/g when LiMn2O4is used as the anode. Tetramethylene sulfone can improve the ionic conductivity of polymer electrolytes, but the other performances are declined. The polymer electrolyte with10%tetramethylene sulfone has good comprehensive performances. The ionic conductivity is5.6×10-3S/cm, the electrochemical stability window is4.25V, the discharge specific capacity is101.3mAh/g when LiMn2O4is used as the anode. Salicylic acid is a more additive for polymer electrolytes.