Preparation And Characterization Of Clay/Poly Ethylene Oxide Polymer Solid Electrolyte System

At present,lithium ion battery has been widely used in portable devices,electric vehicles and so on.Using polymer solid electrolyte will be the development direction of the new generation of lithium ion batteries.Because of its ability of lithium salt solvent,low glass transition temperature and good flexibility,poly ethylene oxide(PEO)becomes a kind of promising solid polymer electrolyte.However,due to the high crystallinity of PEO,the ionic conductivity of PEO based polymer electrolyte is generally not high,only 10-7S/cm or even lower,which can not meet the need of electrolyte for lithium ion batteries.One of the most effective methods is to add inorganic filler in the PEO matrix to inhibit the crystallization of PEO.In these inorganic fillers,layered silicate has become the focus of researches.However,with the development of new materials,the development of higher ionic conductivity and better mechanical properties of polymer solid electrolyte is still a hot research topic.And the selection of inorganic filler has become a key problem.This experiments selected two kinds of inorganic fillers,kaolinite illite,respectively and got some achievements in scientific research.Illite particles were exfoliated by the intercalation and subsequent deintercalation of dimethyl sulfoxide(DMSO)in the interlayer of illite,and the exfoliated illite particles were used to prepare a novel poly(ethylene-oxide)/illite(Illite/PEO)nanocomposite.The resulting exfoliated illite and Illite/PEO nanocomposites were characterized by X-ray diffraction(XRD),infrared spectroscopy(FTIR),scanning electron microscopy(SEM),differential scanning calorimetry(DSC),thermogravimetric analysis(TG),ion conductivity test,thermogravimetry analysis and mechanical test.X-ray diffraction results showed that the acid treatment of illite toexchange K+ in the interlayer of illite with H+ was a necessary condition for the DMSO intercalation.Scanning electron microscopy micrographs confirmed the exfoliation of illite particles in the process of DMSO deintercalation from the interlayer of illite-DMSO intercalation complex.Good dispersion of exfoliated illite in PEO matrix was also confirmed.A gradual decrease in PEO crystallinity in Illite/PEO composites was observed with the increment of the exfoliated illite concentration.The ion conductivity of the composites gradually increased with the filler content and reached 3.21×10-5(S/cm)at an illite mass fraction of 20 wt %.Compared with the PEO/LiClO4 complexes,the ion conductivity improves an order of magnitude.The reason is found that the formation of amorphous region around the exfoliated illite is beneficial for the Li+ ion conduction.The ion conductivity significantly increased when the amorphous regions were connected to each other to form conducting path for Li+ ions with high filler concentration of greater.TG test showed that adding exfoliated illite makes thermal oxidation stability of Illite/PEO nanocomposites system improved significantly.Meanwhile,the mechanical properties of Illite/PEO composites were also enhanced when introducing exfoliated illite into the polymer matrix.The tensile strength of the material achieved the maximum 15.6MPa,when joining the exfoliated illite with mass fraction of 15%.And the elongation at break also achieve maximum.Kaolinite-urea intercalation complex was prepared using kaolinite as intercalation host and urea as intercalating agent.The kaolinite-urea intercalation complex was used as precursor to prepare exfoliated kaolinite by deintercalating urea molecules from the interlayers of kaolinite through ultrasonic treatment.The exfoliated kaolinite particles were used to prepare a novel kaolinite/poly(ethylene-oxide)(Kaolinite/PEO)composite.XRD,FTIR,SEM,DSC,ion conductivity test,thermogravimetry analysis and mechanical test were used to for structure characterization and performance testing.Experimental results confirmed the exfoliation of kaolinite particles with layers thickness were no more than 50 nm.The insert and removal of urea in the layer of kaolinite layer is the main reason of causing the kaolinite exfoliated.FTIR analysis indicated that the hydrogen bondingwas formed between the oxygen atoms of PEO segments and the hydroxyl groups on kaolinite surface,and the interaction between PEO and kaolinite is beneficial to the decrease of crystallinity of PEO.The ion conductivity test results indicated that ion conductivity of the composites gradually increased with exfoliated kaolinite content and reached 6.0×10-5 S/cm at an filler concentration of 20 wt%,which is higher than that of the same filler content in polyethylene oxide/illite composites.It can also be found that the drying temperature has an effect on crystallinity of the PEO.Mechanical properties test results prove that the Young's modulus and tensile strength of the composites were improved because of the introduction of exfoliated kaolinite into EPO matrix.The composites showed the maximum of 256% increase in Young's modulus with 20wt% exfoliated kaolinite and 121% increase in tensile strength with15wt% exfoliated kaolinite.