Influence of solvent type on porosity structure and properties of polymer separator for the Li-ion batteries

Polyethylene-supported polymethyl methacrylate/poly(vinylidene fluoride- co -hexafluoropropylene) separator for gel polymer lithium-ion battery use was prepared with a mixed solvent of n -butanol and acetone. The prepared separator was characterized with scanning electron spectroscopy and X-ray diffraction, and its performance was investigated by electrochemical impedance spectroscopy and battery charge/discharge test. Compared to the separator prepared with acetone, the separator prepared with the mixed solvent shows an enhanced porosity (from 42 to 49 %) and electrolyte uptake (from 104 to 125 %). The ionic conductivity of the corresponding gel polymer electrolyte is improved from 2.81 to 3.39 mS cm −1 , the discharge capacity retention of the LiCoO 2 /artificial graphite battery is increased from 95 to 98 % after 100 cycles at 0.5 C, and the discharge capacity of the battery at 1 C increases by 4 %.