PVDF-based comoposite polymer electrolyte for Li/Lifepo₄ batteries

In order to improve the mechanical strength of the PP/PE/PP membrane, a novel polymer membrane was prepared by introducing nano-SiO₂ filled PVDF polymer film. After soaking the liquid electrolyte (1 mol L^-1 LiPF6 (DMC:DEC:EC=1:1:1, w/w/w)), the composite polymer electrolyte was obtained and used as the electrolyte for Li/LiFePO₄ batteries. The properties of the composite polymer film/electrolyte were characterized by scan electronic microscopy, material test machine, scan voltammetry, electrochemical impedance spectroscopy, constant current charge/discharge test. The results showed that the composite polymer film owns higher electrolyte absorption ability (145 % absorbance) and improved mechanical strength than that of PP/PE/PP film. The ionic conductivity reached 1.12×10^-3 Scm^-1, and its electrochemical stability window is about 4.5V. At 60°C, the capacity retention of Li/LiFePO₄ batteries with the obtained composite polymer electrolyte as electrolyte was 98 % after 100 cycles even at 1C. The excellent cyclability of Li/LiFePO₄ batteries at high temperature showed that the obtained composite polymer electrolyte could be a possible electrolyte candidate for Li/LiFePO₄ batteries used for electric vehicles and hybrid electric vehicles.