Preparation And Application Of Ionic Liquid Modified PVDF-HFP Gel Polymer Electrolyte

Lithium metal battery is a kind of novel energy-storage equipment for new energy sources for its environment benignant,high specific energy and high energy transform efficiency.However,when adopting main component of liquid electrolyte is the organic carbonate,whose is easy to leak and generates gas,meanwhile the dendrite which caused by the nonuniform lithium deposition is probable to induced short circuits,combustion or even explosion.Gel polymer electrolytes or solid polymer electrolytes can avoid the risk of liquid leakage and improve the safety of batteries instead of liquid electrolyte.Solid polymer electrolytes,due to their low ionic conductivity at room temperature and high interfacial impedance,are difficult to apply at room temperature.Gel polymer electrolytes combining the advantages of liquid and solid polymer electrolytes,it is expected to greatly improve the safety of lithium metal batteries.Uneven electric field distribution resulted in nonuniform lithium deposition are the root reason of lithium dendrites.The best way to deal with this problem is to increase mechanical modulus or lithium ion transference number.The inorganic silica can enhance the mechanical properties of the gel polymer electrolyte matrix membrane;the ionic liquid has the advantages of wide electrochemical window,non-volatile,high conductivity,and improves ionic conductivity and electrochemical window of gel polymer electrolyte.Combining the two materials,inorganic silica nanoparticles tethered piperidine ionic liquid?SiO₂PPTFSI?modified PVDF-HFP gel polymer electrolyte was studied in this paper.The main research content is as follows:?1?The SiO₂PPTFSI modified material was synthesized by a three-step method.The mass spectrometry,liquid nuclear magnetic spectroscopy,Fourier transform infrared spectroscopy and solid nuclear magnetic spectroscopy were used to characterize the intermediate and target products.?2?PVDF-HFP nanofibrous membrane was electrospun and spun.Four conditions of spinning solution viscosity,injection speed,operating voltage and polymer molecular weight were studied.The optimum spinning conditions were selected.SiO₂PPTFSI modified nanofibrous membrane was prepared and then it was plasticized with high pressure electrolyte.Scanning electron microscopy?SEM?and dynamic mechanical analysis?DMA?test methods were used to analyze the structure,thermal stability,and mechanical properties.The morphology of electrospun nanofibrous membrane was observed by SEM.The membrane is a three-dimensional network structure constructed from fibers with a diameter of 100-150 nm.The surface of PVDF-HFP fibers is smooth,and the surface of SiO2 and SiO2PPTFSI modified PVDF-HFP fiber is rough.There are many small protrusions.Thermal stability of fibrous membrane is better than that of Celgard membrane.At 120°C,Celgard membrane is obviously curled,while nanofibrous membrane does not shrink or curl and has good stability.The tensile strength and elongation of SiO₂PPTFSI modified membrane were better than those of unmodified PVDF-HFP and SiO₂ modified membrane.The tensile strength was 7.88MPa and the elongation was 135.8%.The membrane has a large specific surface area,a high liquid absorption rate,a full-through pore structure and higher porosity than that of commercial Celgard membrane,which can promote kinetic transmission during the operation of the battery.?3?Chronoamperometry?CA?,alternating current impedance?EIS?,linear scan?LSV?,symmetrical lithium cell cycle,cyclic voltammetry?CV?and so on were tested.compared with unmodified PVDF-HFP electrolyte,SiO₂ modified gel polymer electrolyte?GPE?,and high pressure electrolytes using commercial Celgard separator.Electrochemical performance test shows that SiO₂PPTFSI modified PVDF-HFP GPE has excellent electrochemical performance.It has higher ionic conductivity of 0.639mS cm^-1,larger lithium ion transference number of 0.597,and electrochemical stability up to 5.1 V.For high-voltage lithium batteries,SiO₂PPTFSI modified PVDF-HFP GPE has good compatibility with electrodes can contribute to inhibit formation of lithium dendrites to a certain extent,which makes it suitable for Li/LiNi_0.5Mn_1.5O₄ batteries,showing excellent circulation and rate performance,and ensure the safety of battery.SiO₂PPTFSI modified PVDF-HFP GPE has a broad application prospects.