Influence of different salts in poly(vinylidene fluoride-co-trifluoroethylene) electrolyte separator membranes for battery applications

Abstract

Poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-TrFE) solid polymer electrolytes were prepared using porous membrane soaked in lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), magnesium triflate (Mg(CF3SO3)2) and sodium triflate (Na(CF3SO3)) electrolyte solution. The effect of the uptake of different salts in the morphology, polymer phase, thermal and mechanical properties of the membrane was determined. The electrolyte uptake ranged from 396% for the LiTFSI salt to 529% for the Mg(CF3SO3)2. It is observed that ionic conductivity of the membrane is dependent of the anion size of the salts present in the electrolyte solution. Independently of the electrolyte solution, high ionic conductivity is obtained. In particular, the ionic conductivity for the LiTFSI salt increases from 0.32 to 1.2 mS/cm when the temperature is increased from room temperature to 100 °C. The porous membranes immersed in different electrolyte solutions show good electrochemical stability as determined by cycle voltammetry. It is observed that anion size is very important parameter that affects the uptake value and electric properties of the polymer electrolyte. It is concluded that the polymer electrolyte based on P(VDF-TrFE) porous membranes are adequate for battery separator applications.This work is funded by FEDER funds through the "Programa Operacional Factores de Competitividade - COMPETE" and by national funds by FCT-Fundacao para a Ciencia e a Tecnologia, project references PEST-C/FIS/UI607/2011, PTDC/CTM-NAN/112574/2009, Pest-C/QUI/UIO686/2011 and Grants SFRH/BD/68499/2010 (C.M.C), SFRH/BD/90366/2012 (R. Leones). The authors also thank funding from Matepro - Optimizing Materials and Processes", Ref. NORTE-07-0124-FEDER-000037", co-funded by the "Programa Operacional Regional do Norte" (ON.2 - O Novo Norte), under the "Quadro de Referencia Estrategico Nacional" (QREN), through the "Fundo Europeu de Desenvolvimento Regional" (FEDER)