Evaluation of the main processing parameters influencing the performance of poly(vinylidene fluoride – trifluorethylene) lithium ion battery separators

Poly(vinylidene fluoride – trifluorethylene) membranes are evaluated for lithium ion battery separator applications. Some of the main parameters affecting separator performance such as porosity, dehydration of lithium ions and processing technique (Li-ion uptake versus composite formation) are investigated. The polymer characteristics, as determined by infrared spectroscopy, do not change as a function of porosity, dehydration of lithium ions in the electrolyte solution or processing technique. The electrochemical impedance spectroscopy represented through the Nyquist plot, Bode plot and the ionic conductivity as a function of temperature, strongly depends on the aforementioned paramenters. The membrane that exhibits the highest ionic conductivity is a porous membrane without dehydration of lithium ions and prepared by the uptake technique. The performance of the membrane for battery applications are therefore strongly influenced both by porosity and processing technique.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 Projects PTDC/CTM/69316/2006, project nºF-COMP-01-0124-FEDER-022716 (refª FCT PEst-C/QUI/UI0686/2011) and NANO/NMed-SD/0156/2007, and grants SFRH/BD/68499/2010 (C.M.C) and SFRH/BPD/63148/2009 (V.S.). The authors thank Celgard, LLC for kindly supplying their high quality membranes. The authors also thank support from the COST Action MP1003, 2010 ‘European Scientific Network for Artificial Muscles’