Study The Properties Of PVDF‐based Composite Gel Polymer Electrolyte Prepared By Electrospinning Process

As the transition from liquid lithium ion battery to all solid state lithium ion batteries, gel polymer lithium-ion battery received abroad attention and research because of its long circle-life, high power density and high safety performance. As the important part of the gel polymer lithium ion battery, the research of gel polymer electrolyte has become the current hot point.In this paper, different substances were prepared and used to modify poly(vinylidene fluoride)(PVDF), and three kinds of composite gel polymer electrolytes were prepared by electrospinning technology.1) Polyethylene oxide(PEO) was blent with poly(vinylidene fluoride)(PVDF) in a kind of solution. Then the hybrid microporous membranes(PVDF/PEO) were prepared by electrospinning technology. The morphology was studied by SEM, and the electrochemical performance of the samples was measured as the same time. Meanwhile, it is found that the prepared composite gel polymer electrolyte has best electrochemical properties when the proportion of PVDF and PEO was 5:1 through comparison of the performance of composite gel polymer electrolytes with different ratio. The corresponding ion conductivity at room temperature is 4.5×10-3 S/cm and the electrochemical stability window is up to 4.8 V;2) A novel ion polymer polyurethane lithium salt(PLS) was prepared by condensation polymerization, then PLS was added into PVDF solution. The hybrid gel polymer electrolytes with 3D network structures were prepared by electrospinning technology. The X-ray diffraction(XRD) and differential scanning calorimetry(DSC) test showed that the crystallinity of hybrid gel polymer electrolyte decreased with the added PLS. The electrochemical measurements showed that the ion conductivity and electrochemical stability window of the hybrid polymer electrolyte which contained 20% PLS at room temperature showed best, which are 5.4×10-3 S/cm and 5.0 V, respectively. Moreover the corresponding cell remained 96.8% of the initial capacity after 35 cycles;3) A novel composite particles coating polymer lithium salt in nano-inorganic particle(PML-SiO2) was prepared by dispersion polymerization and sol-gel reaction. The hybrid nano-composites are incorporated into poly(vinylidene fluoride)(PVDF) membranes during the electrospinning process to fabricate a composite nanofibrous membrane. Mechanical properties tests showed that the electrospinning membrane with 8% PML-SiO2 has a high tensile strength 41.28 MPa, and the corresponding composite gel polymer electrolyte which with 3% PML-SiO2 shows the best electrochemical performance. The corresponding cell remained above 90% of the initial capacity after 60 cycles due to the presence of PML-SiO2. The ionic conductivity and electrochemical stability window of it at room temperature are 3.85 × 10-3 S/cm and 4.9 V. At the same time, the reciprocal temperature dependence of ionic conductivity of it follows Arrhenius relation.The prepared composite gel polymer electrolyte has excellent mechanical and electrochemical properties at the same time. We hope the research results could be applied in lithium ion polymer batteries.