Effects Of PVDF-g-MA On Compatiblizer And Properties Of PVDF/TPU Blends

Poly(vinylidene fluoride)(PVDF) is a semi-crystalline polymer with has excellent chemical resistance, high barrier properties and remarkable weathering resistance, and is widely used in industry, electronics and aviation. Therefore, PVDF has been widely used as polymer matrix of gel polymer electrolytes in lithium-ion battery. However, due to the PVDF has a high crystallinity, which leads to the low ionic conductivity. In order to solve above problem, some attempts have been carried out, introducing other blending polymers.Compatibilized of poly(vinylidene fluoride)(PVDF) and thermoplastic polyurethane(TPU) were developed using poly(vinylidene fluoride)-g-(maleic anhydride)(PVDF-g-MA). Study compatibilization of PVDF/TPU by rheological and morphological. Study on mechanical properties, thermal properties and crystallization behavior of GPEs based on PVDF/TPU/PVDF-g-MA(70:30:8) of morphological structure, thermal properties, electrochemical properties and mechanical properties were analyzed.Rheological and morphological structure tests shows that, the compatibility of PVDF/TPU is improved markedly by adding a small amount of PVDF-g-MA. When the addition of PVDF-g-MA(8wt%), the complex viscosity of PVDF/TPU blends was increased, the interface bettween PVDF and TPU becomes fuzzy, particle size of the dispersed phase was reduced. When the addition of PVDF-g-MA(10wt%), the complex viscosity of PVDF/TPU blends was reduced, and particle size of the dispersed phase was increased.The mechanical propertie of PVDF/TPU is improved markedly by adding PVDF-g-MA. When the addition of PVDF-g-MA(8wt%), The tensile strength and ultimate elongation reached the best state with PVDF-g-MA content of 8wt%. The results showed that the vicat softening temperature was improved with increasement of PVDF-g-MA. When the addition of PVDF-g-MA(8wt%), The vicat softening temperature was increased to 66.2 ℃.The result of DSC showed that adding PVDF-g-MA reduced the crystallinty(XC) of PVDF. When the addition of PVDF-g-MA(8wt%), the crystallinty of PVDF was reduced to 42.4%, the melting temperature was increased to 165.7℃. The result of TG showed, with the increasing content of PVDF-g-MA, the T5%, Tmax1, Tmax3 increased. When the addition of PVDF-g-MA(8wt%), The thermal decomposition property reached the best state with PVDF-g-MA content of 8wt%.The PVDF/TPU/PVDF-g-MA blend membrane has a high tensile strength(10.3 MPa) and elongation at break(96.5 %). PVDF/TPU/PVDF-g-MA based gel polymer electrolyte has a high ionic conductivity of 4.7×10-3 S cm-1 with electrochemical stability up to 5.0 V(vs. Li+/Li) at room temperature. The first charge-discharge capacity of PVDF/TPU/PVDF-g-MA based gel polymer electrolyte lithium battery is about 166.9 mAh g-1, which correspond to 98% utilization of theoretical capacity of LiFePO4. After 50 cycles the cell showed a very stable discharge behavior and little capacity loss under current constant voltage conditions. The results reveal that PVDF/TPU/PVDF-g-MA is an excellent polymer matrice as gel polymer electrolyte for lithium ion battery.