The Preparation And Performance Of Adjustable Structure Of Composite Gel Polymer Electrolytes For Lithium-ion Battery

A new type of adjustable structure of alkenyl phosphate ester monomers have been prepared in the thesis. The monomers contained the functional group acrylic ester, soft ethylenedioxy and phosphate, so they were easy to polymerize and had the advantages such as adjustable structure and flame retardant property. Thus the monomers were very suited to synthesize gel polymer electrolytes for Li-ion batteries.The structures of the monomers were characterized by HR-MS, 1H NMR, 31 P NMR,13 C NMR and FT-IR. The homo-polymerization and copolymerization of the alkenyl phosphate ester monomers were synthesized by radical polymerization method. The structures of the polymers were characterized by 1H NMR, 31 P NMR and GPC. The result proved that such monomers had good ability of self polymerization and copolymerization. The good thermal stability of the homopolymers and copolymers were demonstrated by TGA and DSC.The composite gel polymer electrolytes were prepared by the optimized in-situ heat polymerization method. The method was under the vacuum condition of mixing cross-linking agent, free radical initiator, monomers and liquid electrolyte, then reacted for 1 h at 75 ℃ and formed the uniform gel polymer electrolytes. The ionic conductivity and mechanical properties of the gel polymer electrolytes were studied and the gel polymer electrolytes with excellent comprehensive performance were selected. The different conductivity and mechanical property of added nano-SiO2 gel polymer electrolytes were studied. When mixed with 1.5% nano-SiO2, the gel polymer electrolytes had high conductivity and good mechanical property.Furthermore, the self-extinguishing time and flame propagation time of monomer added into the liquid electrolyte were measured by combustion experiments. It turned out that such alkenyl phosphate ester monomers had good flame retardant property.The three-dimensional internal porous structure of the polymer matrix was observed by SEM, which indicated that the gel electrolytes existed good lithium-ions transmission channels inside and leaded to the high conductivity. The alkenylphosphate ester monomer acted as flame retardant was added into liquid electrolyte and fabricated LiFe PO4 liquid electrolyte Li CR2016 Li-ion battery. The battery had excellent charge-discharge curves and cyclic stability, which turned out the monomer had good electrochemical stability and compatibility with the cathode material LiFe PO4. The LiFePO4 GPE Li CR2016 Li-ion battery was also fabricated and had good charge-discharge curves, which proved that the phosphorus containing GPE could be well applied in Li-ion battery and improved safety and stability of Li-ion battery.