PVDF-HFP copolymer

Gozdz et al. (of Bellcore) [25] recognized that poly (vinylidene difluoride) hexafluoropropylene (PVDF HFP) copolymers could form gels with organic solvents and developed an entire battery based on this concept. Typically, the gel separator is 50 pm thick and comprises 60wt. % polymer. In the Bellcore process the separator is laminated to the electrodes under pressure at elevated temperature. The use of the PVDF HFP gelling agent increases the resistivity of the electrolyte by about five times which limits the rate capability of such batteries. 

Apparently, the formation of the microporous structure within the PVdF—HFP copolymer was of critical importance to the success of Bellcore technology, and the ion conductivity was proportional to the uptake of the liquid electrolyte. To achieve the desired porosity of PVdF film, Bellcore researchers prepared the initial polymer blend of PVdF with a plasticizer dibutylphthalate (DBP), which was then extracted by low boiling solvents after film formation. Thus, a pore-memory would be left by the voids that were previously occupied by DBP. However, due to the incomplete dissolution of such high-melting DBP during the extraction process, the pore-memory could never be restored at 100% efficiency. Beside the total volume of pores thus created by the plasticizer. 

Gratzel and co-workers reported the preparation of an electrolyte composed of 10 wt % of PVDF-HFP and the ionic liquid MPII.The PVDF-HFP copolymer is used due to its high dielectric constant, which assists in the dissociation of salts, good electrochemical stability and non-flammability. The HFP units are introduced to reduce the crystallinity degree and increase the solubility of this material in organic solvents. The diffusion coefficients of Ig and 1 in the gel electrolyte were calculated using steady state voltammetry to be 1.9 x 10 cm s and 3.1 x 10 cm s , respectively. 

MICHAEL, M., PRABAHARANS, R.S., Rechargeable hthium battery employing a new ambient temperature hybrid polymer electrolyte based on PVK+PVdF+HFP (copolymer), J. Power Sources, 2004,136(2), 408-15. 

To date, several polymer hosts have been used in GPEs that include PEG, PPO, PAN, PMMA, poly(vinyl chloride) (PVC), PVdF, poly(vinylidene fluoride-hexafluoro propylene) (PVdF-HFP), etc. Furthermore, the Bellcore method and phase inversion method have been developed for the preparation of GPEs. The Bellcore process is critical and developed from the fabrication of PVdF-HFP copolymers. It involves the plasticization of PVdF-HFP copolymers, subsequent plasticizer removal, and the final reswelling in an electrolyte solution. Low-boiling solvents, such as diethyl ether or methanol, are successfully employed to remove dibutyl phthalate (DBF) from the polymer matrix, leaving a pore structure in the polymer layers which is then refilled with the liquid electrolyte during the cell activation process (Song et af, 1999). 

For liquid-based systems, the present state-of-the-art for commercial Li-ion batteries almost universally employs either PVDF homopolymers or PVDF-HFP copolymers for electrode binders and, in some cases, for the electrolyte separator-matrix [52]. These polymers are most effective for commercial processing of composite electrodes on current collector metal foils such as Cu and Al, and... 

Garefa-Payo, M.C., M. Essalhi, and M. KhayeL 2009. Preparation and Characterization of PVDF-HFP Copolymer Hollow Eiber Membranes for Membrane Distillation. Desalination 245(1-3) 469-473. doi 10.1016/j.desal.2009.02.010. 

M.C. Garcia-Payo, M. Essalhi, M. Khayet, Preparation and characterization of PVDF-HFP copolymer hollow fiber membranes for membrane distillation. Desalination, 245... 

Two commercial starting materials, one of Kynar 710 PVDF homopolymer and Kynar Flex 2850 PVDF-HFP copolymer containing 5% HFP and manufactured by Aiicema, Inc. were used. The pellet samples were subjected to e-beam radiation at different doses ranging from 0 to 5 Mrads. Irradiation was carried out under ambient conditions using a medium-energy E-beam gun with 4.5 MeV accelerator. The samples were then used as treated. Some of the properties of neat samples are shown in Table 1. 

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