Preparation And Characterization Of PVDF-based Gel Polymer Electrolyte For Lithium-ion Batteries

Polymer lithium-ion battery is one of the best lithium-ion batteries at present,which is not only flexible on designing the shape of battery,but also shows higher security compared to traditional lithium-ion battery.Gel polymer electrolyte,combining the merits of the security of solid state electrolyte and the high ionic conductivity of liquid electrolyte,which is more promising for the practical application in polymer lithium-ion battery.In this paper,PVDF is used as the substrate material of the gel polymer electrolyte.The chemical grafting and blending methods are used for incorporating poly?glycidyl methacrylate??PGMA?,poly?glycidyl methacrylate-maleic anhydride??P?GMA-MA??and poly?maleic anhydride??PMA?into the PVDF,respectively.SiO₂ with epoxy group and LiClO₄ are further doped into it.Several PVDF microporous membranes are obtained by phase transfer technique and further gelated to prepare the PVDF-based gel polymer electrolytes.In this research,the influences of different weight ratios of GMA and MA on the performance of microporous membranes are investigated.Electrolyte uptake and porosity of electrolyte membrane without gelation are measured.The functional group changes,crystalline and surface morphology of the membranes are characterized by infrared spectrum?IR?,X-ray diffraction spectrum?XRD?and scanning electron microscopy?SEM?,respectively.The electrical conductivity of Li+ ions is determined by measuring electrochemical impedance spectroscopy?EIS?of the PVDF-based gel polymer electrolyte membranes.The charge-discharge curves of the electrolyte membranes are also investigated by using LiFePO₄ and Li CoO₂ as the anode of the lithium-ion batteries,respectively.The results reveal that the membranes with uniform pore structure can be prepared by introduction of LiClO₄ and SiO₂ with epoxy group,meanwhile the degree of crystallinity of the membranes is also reduced.The grafting and blending membranes without gelation have uniform pore structure and show the semi-crystalline state.They are easy to absorb and store liquid electrolyte and gelate the membranes which gives the membranes high conductivity.The electrolyte uptake,porosity and ionic conductivity of PVDF-g-PMA/SiO₂/LiClO₄ are292%,21.3%,39.7 mS/cm,respectively.The charge and discharge performance of this membrance is much better than the other membranes obtained in this paper and the commercial lithium-ion membrane?Celeard 2032?.When LiCoO₂ is used as an anode,theinitial charge and discharge specific capacity of the membrane is 180.9mAh/g and167.1mAh/g,respectively.After 60 cycles,the specific discharge capacity is still maintains138.8mAh/g.