聚丙烯接枝聚乙二醇改性聚丙烯微孔膜

Modification of Polypropylene Microporous Membrane by Blending with Polypropylene-Grafted-Poly(ethylene glycol)

以聚丙烯接枝聚乙二醇(PP-g-PEG)对聚丙烯共混改性,通过单向拉伸工艺制备亲水性聚丙烯微孔膜。使用压汞仪、扫描电镜、Gurley值和水蒸气透过率表征微孔膜的孔结构和透过性能,研究PP-g-PEG含量、PEG接枝率及链长对微孔膜孔结构、水蒸汽透过率及锂电池性能的影响。结果表明,对于接枝率为0.78%的PP-g-PEG,随着添加剂PP-g-PEG含量增加,微孔膜孔隙率和微孔尺寸下降,反映孔道结构的曲挠度及喉孔比上升;微孔膜孔结构与亲水性的综合作用导致水蒸气透过率在PP-g-PEG含量为2.5%时达到最大值。PP-g-PEG含量为2.5%和5.0%的微孔膜组装的锂电池具有较低的电荷转移电阻和较高的充放电比容量,电池性能优于未改性微孔膜组装的电池。提高PEG接枝率使得改性微孔膜孔结构有所变差,但是水蒸气透过率提高,组装电池的性能也更好。长PEG侧链PP-g-PEG对微孔膜孔结构的破坏程度大于短PEG侧链PP-g-PEG,导致组装电池的性能变差。

Polypropylene （PP） was blended with polypropylene grafted polyethylene glycol （PP-g-PEG）, for preparation of hydrophilic PP microporous membranes by uniaxial stretching technology. The porous structures and properties of the microporous membranes were characterized by mercury porosimetry, SEM, Gurley value, and water vapor permeability. The performance of Li-ion batteries assembled with modified membranes was also evaluated. The effects of PP-g-PEG content, grafting degree of PEG, and PEG chain length on the porous structure, permeability of microporous membranes and battery performance were investigated. It is found that, by raising content of PP-g-PEG with 0.78% grafting degree, the porosity and pore size of the membranes drop, the porous tortuosity and thoat/pore ratio increase. The water vapor permeability （WVTR） comes to the maximum at 2.5% PP-g-PEG content, due to the compromising of porous structure and hydrophilie effect. Batteries assembled with modified membranes containing 2.5 % and 5 % PP-g-PEG demonstrate lower complex impedance and specific capacity, much better than the battery assembled with unmodified membrane. Increasing grafting degree of PEG has negative effect on porous structure, but bigger improvement to the hydrophilicity of the membranes, leading to higher WVTR ＇and better battery performance. Pp-goPEG with long PEG chain length deteriorate the porous structure more seriously than PP- g-PEG with short PEG chain length, giving rise to poorer battery performance.