PVDF-HFP Membrane Prepared via TIPS Process as the Matrix of Gel Electrolyte for Lithium Ion Battery

Abstract Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membranes used as the matrix for the gel electrolyte for a lithium battery were prepared via the thermally induced phase separation (TIPS) process using a diluent mixture of dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP). With the assistance of the phase diagram, the membrane microstructure was controlled by only varying the DBP/DEHP ratio in the diluent mixture. The mechanism for the formation of different membrane microstructures was proposed. The effects of membrane microstructure on the membrane performance and the electrochemical properties of the resulting gel electrolyte were also investigated. In addition, a cycle test of a lithium-ion cell with the gel electrolyte based on the membrane prepared via liquid–liquid phase separation showed stable cycling capacity, thus presenting great promise for the use of this membrane as the gel electrolyte matrix for lithium batteries. Keywords: gel electrolyteLi-ion batterymembrane microstructurephase diagramPVDF-HFPthermally induced phase separation This work was supported by the National Basic Research Program of China (no. 2009CB623402) and 863 Program of China (no. 2006AA03Z233).