The influence of
the inclusion of the organic solvent propylene
carbonate (PC) in microporous membranes based on poly(l-lactic
acid) (PLLA) and poly(vinylidene fluoride-co-hexafluoropropylene)
P(VDF-HFP) has been studied based on its relevance for the application
of those separator membranes in lithium-ion batteries. The membranes
have been produced through solvent casting and characterized with
respect to the swelling ratio originated by the uptake of the organic
solvent. The organic solvent uptake affects the porous microstructure
and crystalline phase of both membrane types. The organic solvent
uptake amount affects the crystal size of the membranes as a consequence
of the interaction between the solvent and the polymer, since the
presence of the solvent modifies the melting process of the polymer
crystals due to a freezing temperature depression effect. It is also
shown that the organic solvent partially penetrates into the amorphous
phase of the polymer, leading to a mechanical plasticizing effect.
Thus, the interaction between the organic solvent and the porous membrane
is essential to properly tailor membrane properties, which in turn
will affect lithium-ion battery performance.