Preparation And Application Of Multiphase Structure Of Nano-SiO₂ Composite Electrolyte System

In conventional use of traditional liquid lithium-ion batteries, due to the battery packing damage, the battery overcharge, and lithium dendrite formation in the process of charging and discharging, cause safety problems of electrolyte leakage, short circuit, combustion and explosion, etc. In order to solve the security hidden danger, the researchers used polymer electrolyte instead of the original electrolyte and diaphragm, effectively address these security issues. Compared to liquid electrolyte, the electrical conductivity of polymer electrolyte, lithium ion migration scores and mechanical properties is lower. Therefore, the research and development of new composite electrolyte has a great significance for the development and application of lithium-ion batteries. More current research matrix are: polyvinyl chloride(PVC), polyvinylidene fluoride(PVDF), polyacrylonitrile(PAN), polyethylene oxide(PEO), polymethyl methacrylate(PMMA), etc. Wherein PMMA has good compatibility with the lithium electrode, low interfacial resistance, and has a high ionic conductivity, but the mechanical properties is poor. This paper based on using PMMA as polymer matrix, carries on the modification research. The main work is as follows:(1)The doping nano silicon dioxide were modified. In order to improve the dispersion of silica nanoparticles in polymer matrix, with tetrahydrofuran as the reaction solvent medium, nitrogen was used as protective gas, with potassium tert-butoxide as a modifying additive, 1,3-propane sultone as a modifier on the surface of the graft-modified nano-silica. By single factor experiment, the best modification process conditions were determined, nano-silica surface grafting rate is 78%( Acid-base titration test results)(2)With styrene and trimethylolpropane triacrylate to take cross-linking copolymerization. nitrogen as a protective atmosphere, azobisisobutyronitrile as initiator, by the in situ polymerization successfully prepared of the composite polymer material SiO2/P(MMA-S), the prepared composite polymer has moderate cross-linking degree, a good film-forming properties.(3)By phase inversion method to complete the preparation of the porousstructure of the composite membrane with composite polymer material. N,Ndimethylacetamide and acetone as a mixed solvent, polyvinyl pyrrolidone as a binder, with deionized water as non solvent phase, successfully prepared porous membrane material.(4)Taking LiClO4-DMC/EC/EMC as lithium salt electrolyte, the composite polymer electrolyte membrane SiO2/P(MMA-S) were assembled into a test cell. By testing, the absorption rate up to 310%, in the weighing bottle in glove box after 15 days, the weight loss rate not more than 20%. The tensile strength can reach above 40 Mpa, the elongation at break up to more than 40%. The conductivity of composite polymer electrolyte membrane at room temperature was up to 3.98×10-3S/cm, the electrochemical window is 5.48 V. Under the ratio of 0.1C and 0.2C, the first discharge capacity is 156.8 mAh·g-1 and 147.6 mAh·g-1. The capacity retention rate could reach 93.5% and 91.4% in the ratio of 0.1C and 0.2C and under 30 times cycle test.