Effect of fiber orientation in gelled poly(vinylidene fluoride) electrospun membranes for Li-ion battery applications

Battery separators based on electrospun membranes of poly(vinylidene fluoride) have been prepared in order to study the effect of fiber alignment on the performance and characteristics of the membrane. The prepared membranes show an average fiber diameter of ~272 nm and a degree of porosity of ~ 87%. The gel polymer electrolytes are prepared by soaking the membranes in the electrolyte solution. The alignment of the fibers improves the mechanical properties for the electrospun membranes. Further, the microstructure of the membrane also plays an important role in the ionic conductivity, being higher for the random electrospun membrane due to the lower tortuosity value. Independently of the microstructure, both membranes show good electrochemical stability up to 5.0 V versus Li/Li+. These results show that electrospun membranes based on poly(vinylidene fluoride) are appropriate for battery separators in lithium ion battery applications, the random membranes showing a better overall performance.This work is funded by FEDER funds through the "Programa Operacional Factores de Competitividade – COMPETE" and by national funds by FCT- Fundação para a Ciência e a Tecnologia, project references Project PTDC/CTM/69316/2006, NANO/NMed-SD/0156/2007 and Pest-C/QUI/UIO686/2011 and grant SFRH/BD/68499/2010 (C.M.C) and SFRH/BD/66930/2009 (J.N.P.) SFRH/BPD/63148/2009 (V.S). The authors thank Celgard, LLC for kindly supplying their high quality membrane