Effect of the microsctructure and lithium-ion content in poly[(vinylidene fluoride)-co-trifluoroethylene]/lithium perchlorate trihydrate composite membranes for battery applications
Poly[(vinylidene fluoride)-co-trifluoroethylene] membranes doped with different lithium perchlorate trihydrate contents have been produced by solvent evaporation at different temperatures in order to tailor membrane morphology and characterized by infrared spectroscopy, thermal and mechanical analysis techniques. Electrochemical properties of the composite membranes for battery applications were determined through complex impedance spectroscopy and cyclic voltammetry. The polymer phase and molecular main features of the polymer do not depend on lithium ion content and crystallization temperature. Higher crystallization temperatures allow obtaining more porous polymer microstructures which strongly influences the electrical response. The degree of crystallinity and ionic conductivity, on the other hand, are related to lithium ion content. The obtained ionic conductivity determined by impedance spectroscopy increases with increasing lithium ion content. The most conducting electrolyte composition, PVDF-TrFE 1.5LiClO4.3H2O exhibits 2.3 x 10- 6 S cm- 1 and corresponds to the membrane crystallized at room temperature, i.e. the most porous membrane.