| With the increasingly contradiction between energy supply and demand,people began to focus on the lighter and more efficient energy storage devices.No matter what device,electrolyte is an indispensable part of it.As an emerging electrolyte,gel polymer electrolyte combines the safety of solid electrolyte and the high ionic conductivity of liquid electrolyte.It has been developed since the early 1970s and after decades of research,it has played an indispensable role in more and more fields.This thesis takes PVDF-HFP based gel polymer electrolyte as the research object.Using the solution casting method,LiClO4 as the lithium salt,PVDF-HFP as the polymer matrix,acetone as the solvent,PVDF-HFP based gel polymer electrolyte membrane was prepared.We conducted a series of mechanical,thermal and electrochemical experiments to optimize it.It is then doped with inorganic powder to further enhance the ionic conductivity of the composite membrane and increase its application potential in the field of electrochromism.The main research contents and results are as follows:1.PVDF-HFP based gel polymer electrolytes were prepared by solution casting method,and the effects of the matrix,plasticizer and lithium content on the structure and properties of the electrolyte have been investigated.The tensile test results showed that the higher the PVDF-HFP matrix content and the lower the PC content,the higher Young's modulus of the gel system,the better the mechanical properties,while the corresponding ionic conductivity will decrease.When the mass fraction of LiClO4 is 3%,the ionic conductivity of the corresponding gel film is the highest,and the ionic mobility is upto 0.960.The gel film has a wide working window,and the best mass ratio of gel film is PVDF-HFP:LiClO4:PC:acetone=9:3:20:68 among all data.At this time,Young's modulus of the gel film is about 1.91 MPa,the fracture strain is upto 230%,and the ionic conductivity is about 6.43×10-4 S/cm.The inorganic nano SiO2 doping gel film shows that the mechanical properties of the gel film can be greatly enhanced,and Young's modulus can reach about 16.9 MPa and the fracture strain reaches about 590.5%.At the same time,compared with undoped gel film,the liquid retention rate increased and showed better thermodynamic stability.2.Through emulsification,KH-570 was used as the silane coupling agent,methyl methacry?MMA?as the polymer monomer,potassium persulfate?KPS?as the initiator and finally the PMMA-coated SiO2?SiO2-PMMA?was successfully prepared.We doped the modified powder to prepare the PVDF-HFP based gel polymer composite electrolyte film,and characterized its structure and electrochemical performance in detail.The results show that by doping SiO2 and SiO2-PMMA nanospheres,the ion conductivity of the gel film can be improved,and the optimal ion conductivity is 1.33×10-3 S/cm and 2.22×10-3 S/cm,the corresponding optimal doping concentrations are 4 wt%?SiO2?and 10 wt%?SiO2-PMMA?respectively.The simultaneous increase in doping concentration and ionic conductivity can be attributed to the better compatibility of SiO2-PMMA in PVDF-HFP matrix compared to unmodified SiO2 nanospheres,which enables SiO2 nanopowder disperse better in PVDF-HFP matrix.At the same time,the coating layer PMMA and PVDF-HFP have the effect of blending modification.3.KH-570 was used to modify the nano-TiO2 powder,and the effect of PH value on the hydrolysis modification effect of silane coupling agent was studied.The results show that under acidic conditions,PMMA can be better coated on the surface of TiO2,mainly because acidic conditions inhibit the polycondensation reaction of the silanol hydrolysate,but alkaline conditions are conductive to the polycondensation reaction of silanol.Therefore in the first step,a large proportion of silanol undergoes self-polymerization and the KH-570 grafted on the surface of TiO2 decreases,which ultimately results in the second step,only o small part of PMMA is coated on the surface of the inorganic particles,mostly of PMMA undergoes self-condensation to form PMMA blocks.Comparing TiO2-PMMA and SiO2-PMMA,it can be found that the particle size of TiO2-PMMA spheres is smaller.When doped with the two kinds of modified powder,under the same conditions,the ion conductivity of the doped SiO2-PMMA gel film is higher,mainlt due to the larger dielectric constant of TiO2particles.Higher dielectric constant can dissociate more free lithium ion charge.The optimal ion conductivity is 1.564×10-3 S/cm and 2.568×10-3 S/cm,the corresponding optimal doping concentrations are 5 wt%?TiO2?and 7wt%?TiO2-PMMA?respectively. |
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