纳米复合全固态聚膦腈电解质

ALL-SOLID-STATE POLYPHOSPHAZENE NANOCOMPOSITE ELECTROLYTE

为了进一步提高聚合物电解质的室温离子电导率和锂离子的迁移数,通过对纳米二氧化硅的表面修饰,并采用可聚合的带氧化乙烯-氧化丙烯共聚侧链取代的聚膦腈大单体制备了纳米复合的全固态电解质.通过X射线光电子能谱,扫描电镜,差热扫描分析对纳米复合电解质的性能和形貌进行了分析,并通过交流阻抗考察了电解质与电极间的界面稳定性,用循环伏安表征了电解质的电化学稳定窗口,考察了锂盐含量对电解质离子电导率的影响,测试了电解质的离子电导率随温度的关系,并对锂离子的迁移数进行了测定.研究结果表明,通过纳米复合的方法,提高了聚合物电解质的离子电导率,降低了界面电阻,提高了锂离子迁移率.

In 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 nanoSiO2 modified with poly- （oxyethylene-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 tfimethyloxyl siloxane and allyl poly （ethylene-co-propylene glycol） methyl ether. The silane coupling agent refluxed with SiO2 to form nanoSiO2 modified with poly（oxyethylene-co-oxypropylene） silane. The FT-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 nanoSiO2 content in electrolyte fixed at 10% could reach the best ambient conductivity of 3.14×10^-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 nanoSiO2 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~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 can be explained on 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 can 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 nanoSiO2 reduces the formation of ion chlster. Cyclic voltammogram gives the result of good electrochemical stability of nanocomposite electrolyte and an electrochemical window of more than 4.2 V. Alternating current impedance spectrum accounts for the good interracial 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 interracial impedance and help the transfusion of ions. The diffusion number of lithium ion in the nanocomposite all-solid-state polymer electrolyte is realized through stable current method, the result indicates that the ion diffusion number increased from 0.25 to 0.34 due to the composite of nanoparticles.