Study of the mechanical and electrical properties of carbon/poly(vinylidene fluoride-tetrafluoroethylenepropylene) films crosslinked with triethylenetetramine: Possible application as binder for lithium-ion battery electrodes

The mechanical properties of poly(vinylidene fluoride-tetrafluoroethylene-propylene) (PVDF-TFE-P) were evaluated as a function of the degree of crosslinking. Both bisphenol and triethylenetetramine (TETA) were used as crosslinkers to improve the mechanical properties of PVDF-TFE-P and carbon black-filled PVDF-TFE-P. Bisphenol was incorporated into the polymer by the manufacturer and crosslinking was achieved through additions of MgO and CaO followed by heating. Although bisphenol crosslinking improves the mechanical properties, further crosslinking was needed to obtain good extensibility under repeated deformation of carbon black/PVDF-TFE-P composites. By incorporating small amounts of 1,4-diazabicyclo[2.2.2]octane and CaO, additions of TETA added more crosslinks in PVDF-TFE-P, leading to improved mechanical and electrical properties. The crosslinked polymer does not become brittle in typical solvents used in lithium battery electrolytes, so we believe that this highly extensible binder system may be useful for electrode materials that show large volume changes during charge-discharge cycling. (C) 2004 Wiley Periodicals, Inc.