All-solid-state polyphosphazene nanocomposite electrolyte

lit order to improve the ambient conductivity of all-solid-state electrolytes as well as enhance the diffusion number of lithium ion,all-solid-state polyphosphazene electrolytes containing nanoSiO(2) modified with polyoxyethylene-co-oxypropylene) silane were prepared. The macromonomer of polyphosphazene was prepared through reaction of phosphazene with poly (oxyethylene-co-oxypropylene) monoacrylic ester and poly (ethylene glycol) monomethylether with the yield of 92.6%. Silane Coupling agent with polyether was prepared by the hydrosiloxane addition reaction between trimethyloxyl siloxane and allyl poly (ethylene-co-propylene glycol) methyl ether. The silane coupling agent refluxed with SiO2 to form nanoSiO(2) modified with poly(oxyethylene-co-oxypropylene) silane. The FF-IR spectrum and XPS together show that SiO2 has been Successfully modified by the soft chain. The SEM images of composite electrolytes show that modified nano SiO2 could easily disperse among polymer electrolyte with only a little conglomeration. It is found that the nanoSiO(2) content in electrolyte fixed at 10% could reach the best ambient conductivity of 3.14 x 10(-4) S cm(-1), which is 2.4 times higher than that of the noncomposite system. Differential scanning calorimetry of nanocomposite solid state electrolytes showed that the glass transition temperature of the electrolyte did not change with the variation of nanoSiO(2) content from 2% to 10% , which indicated that nano SiO2 modified with polyether did not change the crosslinking density of nanocomposite system, and the polyether chain could maintain the original flexibility of the solid state electrolytes. The conductivity of electrolyte is increasing with the increase of temperature, Which obeys the VTF equation. When the temperature rises up to 50 degrees C, the electrolyte with 10% modified SiO2 shows the best conductivity of 10(-3) S cm(-1) the corresponding active energy is 4.07 kJ mol(-1) The high conductivity call be explained oil the one hand, the polyphophazene monomer has the side chain of oxyethylene,which is helpful to solve the lithium salt, the copolymerization of oxyethylene and oxypropylene reduces the glass transition temperature of the polymer and inhibits the crystallization of polyoxyethylene; on the other hand,the nanoparticles modified with soft polyether chains call uniformly disperse in the polymer electrolyte, and the polyether plays the role of plasticizer. The result of DSC also proves such explanation. With increasing the content of lithium Salt,the ionic conductivity first increases, then shows a subsequent decline. The highest ambient conductivity of nanocomposite electrolyte is obtained when the concentration of lithium perchlorate is fixed at 8%. The addition of nanoSiO(2) reduces the formation of ion cluster. Cyclic voltammogram gives the result of good electrochemical stability of nanocomposite electrolyte and all electrochemical window of more than 4.2 V. Alternating current impedance spectrum accounts, for the good interfacial stability between electrolyte and electrode after 7 days of the assembling of the cell,which was explained by the composition of nanoparticles modified with flexible chains which may reduce the interfacial impedance and help the transfusion of ions. The diffusion number of lithium]oil in the nanocomposite all-solid-state polymer electrolyte is realized through stable current method, the result indicates that theion diffusion number increased from 0.25 to 0.34 due to the composite of nanoparticles.