Effect of the degree of porosity on the performance of poly(vinylidene fluoride-trifluoroethylene)/poly(ethylene oxide) blend membranes for lithium-ion battery separators

• P(VDF-TrFE)/PEO blends have been developed for battery separator applications.
• PEO removal from the membrane increases degree of porosity and electrical properties.
• After 90% PEO removal membranes show 44% porosity and a conductivity of 0.54 mS cm− 1.
• After 90% PEO removal it is obtained 124 mAhg− 1 at C/5 and 47 mAhg− 1 at 2C.
• This polymer blends are promising separators for Li-ion battery applications.

Porous polymer membranes based on poly(vinylidene fluoride-trifluoroethylene)/poly(ethylene oxide) copolymers, P(VDF-TrFE)/PEO, are prepared through elimination (from partial to total) of PEO, leading to interconnected micropores in the polymer blends.Electrolyte uptake, thermal and mechanical properties depend on the amount of PEO present in the polymer blend. Further, the degree of crystallinity of PEO and the elastic modulus (E′) of the polymer blend decrease with increasing PEO removal.Electrical properties of the polymer blend membranes are influenced by the porosity and are dominated by diffusion. The temperature dependence of the ionic conductivity follows the Arrhenius behavior. The ionic conductivity is the highest for the membranes with a volume fraction of pores of 44% (i.e., 90% PEO removal), reaching a value of 0.54 mS cm− 1 at room temperature.Battery performance was determined by assembling Li/C-LiFePO4 swagelok cells. The polymer blends with 90% PEO removal exhibit rate (124 mAhg− 1 at C/5 and 47 mAhg− 1 at 2C) and cycling capabilities suitable for lithium ion battery applications.